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INVASIVE'PLANT'SPECIES'IMPACTS'ON'CARBON'AND'NITROGEN'CYCLING'IN'INLAND'
MICHIGAN'WETLANDS'
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By'
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Jason'Philip'Martina'
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A'DISSERTATION'
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Submitted'to'
Michigan'State'University'
in'partial'fulfillment'of'the'requirements'
for'the'degree'of'
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DOCTOR'OF'PHILOSOPHY'
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Plant'Biology'
Ecology,'Evolutionary'Biology'and'Behavior'
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2012'
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ABSTRACT'
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INVASIVE'PLANT'SPECIES'IMPACTS'ON'CARBON'AND'NITROGEN'CYCLING'IN'INLAND'
MICHIGAN'WETLANDS'
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By'
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Jason'Philip'Martina'
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Plant'traits'are'often'the'central'focus'of'ecological'investigations'into'ecosystem'

structure'and'function'because'of'the'need'to'simplify'complex'plant'communities'to'a'few'
traits'of'importance.''Invasions'by'invasive'species'can'have'major'impacts'on'ecosystem'
function'by'altering'the'presence'and/or'dominance'of'plant'traits'that'influence'
ecosystem'energy'flow'and'nutrient'cycling.''The'broad'goal'of'this'dissertation'was'to'
investigate'the'ecosystem'consequences'of'invasive'plant'species'in'temperate'wetlands,'
which'are'important'ecosystems'for'the'cycling'of'carbon'(C)'and'nitrogen'(N),'focusing'on'
Phragmites+australis+(Cav)'Trin.'Ex'Steud,+Phalaris+arundinacea'L.'and'Typha+ × glauca'Godr.'
X.''I'hypothesized'that'within'inland'Michigan'wetlands,'the'degree'of'invasion'would'be'

€
correlated'with'increased'C'and'N'stocks'due'to'the'high'production'of'low'quality'litter'
from'these'invasive'plants.''I'found'evidence'that'both'soil'and'ecosystem'C'stocks'
increased'due'to'the'presence'of'these'invasive'species.''Additionally,'I'found'significant'
differences'for'C'and'N'mineralization'among'species'linked'to'the'quality'of'their'litter'
(C:N'ratios),'with'P.+australis'soil'having'the'lowest'C'and'N'mineralization'and'P.+
arundinacea'soil'the'highest.'
Phragmites+australis'is'a'tall,'high'biomass'invasive'species'that'is'a'relatively'recent'
invader'into'the'wetlands'of'the'Great'Lakes'states.''To'investigate'the'effects'of'living'
biomass'and'litter'on'C'and'N'cycling,'I'manipulated'P.+australis'litter'and'biomass'within'

plots'at'three'wetland'sites'and'then'monitored'abiotic'conditions'and'performed'a'
number'of'biogeochemical'assays.''Removing'P.+australis'litter'and'biomass'had'the'
hypothesized'effects'of'increasing'light'levels'at'the'soil'surface'and'increasing'soil'
temperature,'though'these'effects'did'not'influence'litter'bag'decomposition,'in+situ'N'
mineralization,'or'potential'denitrification'rates.''Biomass'removal'did'affect'porewater'ion'
concentrations'by'decreasing'Na+,'Cl]'and'Ca2+'concentrations'and'increasing'NO3]'
concentration.''Though'not'initially'hypothesized,'all'C'and'N'cycling'rates'showed'strong'
site'effects'caused'by'different'hydrologic'conditions'among'sites.'''
To'separate'litter'quality,'litter'diversity,'and'soil'origin'from'other'controls'of'
decomposition,'I'performed'two'laboratory'incubations'using'litter'and'soil'collected'from'
monospecific'stands'of'the'three'focal'invasive'species'plus'Carex+lacustris,'a'native'sedge.'I'
found'support'for'my'prediction'that'the'four'species'differed'in'litter'quality'and'that'litter'
C:N'ratio'was'negatively'related'to'C'and'N'mineralization'rates.''I'also'found'strong'soil'
origin'effects'related'to'soil'nutrient'availability,'which'have'not'been'found'before'within'a'
similar'experimental'framework.''The'second'incubation'showed'that'while'litter'diversity'
significantly'affected'litter'decomposition'rates,'the'effects'were'more'dependent'of'the'
identity'of'the'species'than'just'the'number'of'species.'''
Taken'together,'these'results'suggest'that'invasive'species'can'influence'C'and'N'
cycling'in'inland'Michigan'wetlands,'and'that'some'of'the'biogeochemical'effects,'like'
increased'C'storage,'could'be'a'positive'outcome'of'invasion.''These'effects'can'also'be'
linked'to'key'plant'traits,'such'as'litter'quality'and'biomass'production,'and'supports'the'
conjecture'that'invasive'species'alter'ecosystem'function'by'changing'the'composition'or'
dominance'of'plant'traits'within'the'community.'

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This'work'is'dedicated'to'my'grandmother,'Helen'Dombrowski.'''
Thank'you'for'believing'in'me.'
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ACKNOWLEDGEMENTS'
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I'would'like'to'thank'my'advisors,'Dr.'Stephen'K.'Hamilton'and'Dr.'Merritt'Turetsky,'
for'their'guidance'throughout'this'project.''They'both'showed'great'patience'with'me'
throughout'the'entire'process,'especially'when'I'was'writing.''Without'their'help'and'
support'I'wouldn’t'have'been'able'to'complete'this'task.''I'am'also'grateful'to'my'
committee'members,'Dr.'Kay'Gross'and'Dr.'Jay'Lennon'for'their'direction'on'experimental'
design'and'comments'on'early'drafts'of'this'dissertation.''Assistance'from'multiple'people'
made'this'research'possible.''I'had'a'great'group'of'undergraduates'help'with'this'project'
including'Colin'Phillippo,'Spencer'Rubin,'Ryan'O’Connor,'Matt'Chansler,'Matt'Kolp,'and'
Claire'Moore.''I'am'so'proud'of'all'of'them.''Special'thanks'goes'to'all'members'of'the'
Hamilton'and'Turetsky'Labs,'especially'Dave'Weed'for'all'of'his'laboratory'assistance.''
Leila'Siciliano'provided'additional'field'and'laboratory'assistance.''Thanks'to'all'the'faculty,'
graduate'students,'and'staff'at'MSU'and'KBS'who'have'helped'me'get'through'my'classes,'
thesis'writing,'and'experimentation.''The'list'would'be'too'long'to'write,'but'you'know'who'
you'are.''Thank'you.'
I'would'also'like'to'thank'Dr.'David'Rothstein'and'his'lab'members,'Ellen'Holste,'
Mike'Cook,'and'Tom'Baribault,'for'the'guidance'they'gave'on'chemical'analysis'and'for'
allowing'me'to'routinely'use'their'laboratory.'''Dr.'Stuart'Grandy'and'Cynthia'Kallenbach'
also'allowed'me'to'use'their'laboratory'and'equipment.''Thanks'to'Dr.'Jen'Tank'at'the'
University'of'Notre'Dame'and'her'graduate'student,'Sarah'Roley,'for'guiding'me'through'
the'denitrification'assays.''I'am'indebted'to'Dr.'Carl'von'Ende'at'Northern'Illinois'
University'for'the'training'he'gave'me'before'entering'the'doctoral'program'at'MSU'and'for'

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statistical'guidance.''A'huge'thank'you'goes'to'Dr.'Andy'Jarosz'and'his'lab,'specifically'Josh'
Springer,'for'taking'me'in'and'allowing'me'to'use'their'lab'and'resources'when'I'had'no'
where'else'to'go.''I'will'always'value'our'lab'meetings'together'and'friendship.'''
Funding'for'this'research'was'provided'by'an'Environmental'Protection'Agency'
STAR'Fellowship,'a'Society'of'Wetland'Scientists'Research'Grant,'a'LTER'Small'Grant,'a'
Biogeochemistry'Environmental'Research'Initiative'Grant,'a'College'of'Natural'Science'
Continuation'and'Completion'Fellowship,'the'MSU'Graduate'School,'the'Paul'Taylor'
Endowment'Fund,'the'Department'of'Plant'Biology,'the'Kellogg'Biological'Station,'and'the'
Ecology,'Evolutionary'Biology'and'Behavior'Program.''
I'am'very'grateful'for'the'support'I'received'from'my'parents,'Joseph'and'Judi'
Martina,'and'my'brother,'Eric'Martina.''You'are'an'amazing'group'of'people'who'I'strive'to'
be'more'like'everyday.''Most'importantly,'I'would'like'to'thank'Leila'Siciliano.'Without'
your'help,'support,'love,'and'infinite'patience'none'of'this'would'have'been'possible.''
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TABLE'OF'CONTENTS'
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LIST'OF'TABLES.....................................................................................................................................................ix'
LIST'OF'FIGURES................................................................................................................................................. xii'
CHAPTER'1'
INTRODUCTION......................................................................................................................................................1'
1. Carbon'and'Nitrogen'Cycling'in'Wetlands....................................................................................1'
2. Invasive'Species'and'Plant'Functional'Traits..............................................................................8'
3. Decomposition:'Abiotic'and'Biotic'Determinants.................................................................. 15''''
4. Research'Objectives ............................................................................................................................ 20'
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CHAPTER'2'
ORGANIC'MATTER'ACCUMULATION'AND'QUALITY'IN'MICHIGAN'WETLANDS:'
CONSEQUENCES'OF'INVASIVE'PLANTS ................................................................................................... 24'
1. Brief'Rationale ....................................................................................................................................... 24'
2. Objectives,'Hypotheses,'and'Predictions ................................................................................... 26'
3. Methods .................................................................................................................................................... 28'
a. Study'sites'and'sampling'for'wetland'survey............................................................ 28'
b. Carbon'and'nitrogen'analysis........................................................................................... 30'
c. Estimation'of'plant'abundance' ....................................................................................... 31'
d. Soil'carbon'quality'assay .................................................................................................... 32'
e. N'mineralization'and'nitrification'assay ..................................................................... 35'
f. Statistical'analyses ................................................................................................................ 37'
i. Wetland'survey ........................................................................................................ 37'
ii. Assays'of'C'quality'and'N'transformations .................................................. 39'
4. Results....................................................................................................................................................... 41'
a. Wetland'survey....................................................................................................................... 41'
b. Soil'carbon'quality'assay .................................................................................................... 44'
c. N'mineralization'and'nitrification'assay ..................................................................... 46'
5. Discussion................................................................................................................................................ 62'
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CHAPTER'3'
EFFECTS'OF'ABOVEGROUND'BIOMASS'AND'LITTER'ON'BIOGEOCHEMICAL'CYCLING'IN'
PHRAGMITES+AUSTRALIS'STANDS .............................................................................................................. 70'
1. Brief'Rationale ....................................................................................................................................... 70'
2. Objectives,'Hypotheses,'and'Predictions ................................................................................... 72'
3. Methods .................................................................................................................................................... 74'
a. Site'description'and'experimental'treatment'design............................................. 74'
b. Abiotic'and'biotic'measurements ................................................................................... 77'
c. Litter'bag'decomposition'assay....................................................................................... 79'
d. Porewater'equilibrators ..................................................................................................... 80'
e. N'mineralization'and'nitrification'assays ................................................................... 81'
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f. Denitrification'assay............................................................................................................. 82'
g. Statistical'analyses ................................................................................................................ 84''''''
4. Results....................................................................................................................................................... 90'
a. Site'characteristics ................................................................................................................ 90''''
b. Litter'and'AGB'effects'on'soil'and'porewater'chemistry,'light'levels,'and'
temperature ............................................................................................................................. 92'
c. Carbon'and'nitrogen'cycling ............................................................................................. 94'
5. Discussion............................................................................................................................................. 123'
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CHAPTER'4'
EFFECTS'OF'LITTER'QUALITY,'SOIL'ORIGIN,'AND'PLANT'SPECIES'DIVERSITY'ON'
DECOMPOSITION'IN'TEMPERATE'WETLANDS ................................................................................. 132'
1. Brief'Rationale .................................................................................................................................... 132'
2. Objectives,'Hypotheses,'and'Predictions ................................................................................ 134'
3. Methods ................................................................................................................................................. 136'
a. Litter'quality'and'soil'origin'incubation ................................................................... 136'
i. Site'description'and'sample'processing..................................................... 136'
ii. Carbon'mineralization'assay........................................................................... 139'
iii. N'mineralization/nitrification'assay ........................................................... 140'
b. Litter'diversity'incubation .............................................................................................. 141'
i. Site'description'and'sample'processing..................................................... 141'
ii. Carbon'mineralization'assay........................................................................... 143'
iii. N'mineralization/nitrification'assay ........................................................... 144'
c. Statistical'analysis .............................................................................................................. 145'
4. 'Results................................................................................................................................................... 147'
a. Litter'quality'and'soil'origin'incubation ................................................................... 147'
b. Litter'diversity'incubation .............................................................................................. 150'
5. Discussion............................................................................................................................................. 167'
a. Litter'quality'and'soil'origin'incubation ................................................................... 167'
b. Litter'diversity'incubation .............................................................................................. 172'
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CHAPTER'5'
CONCLUSIONS ................................................................................................................................................... 175'
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APPENDICES ...................................................................................................................................................... 185'
1. Appendix'A ........................................................................................................................................... 186'
2. Appendix'B ........................................................................................................................................... 192'
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REFERENCES ..................................................................................................................................................... 194'
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LIST'OF'TABLES'
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Table'2]1.''GPS'coordinates'of'the'24'survey'sites'with'their'hydrological'classification,'
which'is'based'on'magnesium'concentrations'(see'methods'for'more'details),'and'the'
presence'or'absence'of'the'most'dominant'invasive'species.'Phalaris'='Phalaris+
arundinacea,'Typha'='Typha'xglauca,'Phragmites'='Phragmites+australis. ...................................40'
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Table'2]2.'Summary'of'the'best]fit'model'for'biomass'C'and'N'stocks.''Dominance'refers'to'
the'proportion'of'the'total'biomass'from'invasive'or'native'species.''Terms'in'bold'indicate'
significant'predictors.''Df'(Den)'indicates'the'denominator'degrees'of'freedom. ....................48'
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Table'2]3.'Summary'of'the'best]fit'model'for'litter'C'and'N'stocks'and'litter'C:N'ratios.''
Terms'in'bold'indicate'significant'predictors.''Df'(Den)'indicates'the'denominator'degrees'
of'freedom. ................................................................................................................................................................48'
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Table'2]4.'Summary'of'the'best]fit'model'for'soil'C'and'N'stocks'and'soil'C:N'ratios.''Terms'
in'bold'indicate'significant'predictors.''Df'(Den)'indicates'the'denominator'degrees'of'
freedom. .....................................................................................................................................................................49'
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Table'2]5.'Summary'of'the'best]fit'model'for'ecosytem'C'and'N'stocks.''Terms'in'bold'
indicate'significant'predictors.''Df'(Den)'indicates'the'denominator'degrees'of'freedom....49'
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Table'2]6.'Results'of'repeated'measures'ANOVA'for'the'effect'of'Species,'Temperature'and'
Time'on'C'mineralization'throughout'the'36'day'incubation ............................................................50''
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Table'2]7.'Summary'of'ANOVA'examining'the'effect'of'Species'and'Temperature'on'
cumulative'C'mineralization. ............................................................................................................................50''
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Table'2]8.'Soil'and'litter'%C,'%N,'and'C:N'ratio'of'the'four'species'used'in'the'organic'
matter'quality'incubation.''Same'letter'superscript'denotes'nonsignificant'differences'
according'to'Tukey'post'hoc'tests.'Values'are'means'±'SE..................................................................51'
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Table'2]9'Soil'%C,'%N,'and'C:N'ratio'of'the'four'species'used'in'the'N'
mineralization/nitrification'incubation.''Same'letter'superscript'denotes'nonsignificant'
differences'according'to'Tukey'post'hoc'tests.'Values'are'means'±'SE..........................................51'
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Table'3]1.''Variation'among'sites'in'plant'characteristics,'soil'characteristics,'and'water'
chemistry.'Variance'expressed'as'standard'error.'AGB'='aboveground'biomass,'DO'='
dissolved'oxygen,'SpC'='specific'conductivity,'ORP'='oxidation'reduction'potential,'OM'='
organic'matter.'*'indicates'data'collected'in'2010. .................................................................................86'
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Table'3]2.'Mixed'model'F]values'for'the'effect'of'Site'and'Depth'on'Bulk'Density,'
Ammonium,'Nitrate,'Soil'%C,'Soil'%N,'Soil'C:N'ratio,'and'Soil'C'and'N'Stock.''df'indicates'
degrees'of'freedom.''Significance'is'denoted'with'asterisk(s)...........................................................97'
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Table'3]3.'Mixed'model'F]values'for'the'effect'of'Treatment'and'Depth'on'Bulk'Density,'
Ammonium,'Nitrate,'Soil'%C,'Soil'%N,'Soil'C:N'ratio,'and'Soil'C'and'N'Stock.''df'indicates'
degrees'of'freedom.''Significance'is'denoted'with'asterisk(s)...........................................................97'
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Table'3]4.'Summary'of'two]factor'ANOVA'for'the'effect'of'Treatment'and'Depth'on'soil'
temperature.'den'df'indicates'the'denominator'degrees'of'freedom'and'num'df'indicates'
numerator'degrees'of'freedom. .......................................................................................................................98'
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Table'3]5.'Summary'of'Repeated'Measures'ANOVA'for'the'effect'of'Treatment,'Depth,'and'
Time'on'soil'temperature'during'the'2010'growing'season.''den'df'indicates'denominator'
degrees'of'freedom'and'num'df'indicates'numerator'degrees'of'freedom. .................................98'
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Table'3]6.'Mixed'model'F]values'for'the'effect'of'Treatment'and'Depth'on'TDP'(total'
dissolved'phosphate),'Mg2+,'Ca2+,'Na+,'K+,'SO42],'Cl],'and'NO3]'concentrations'from'
porewater'equilibrators.'Significance'is'denoted'with'asterisk(s).'df'indicates'degrees'of'
freedom. .....................................................................................................................................................................99'
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Table'3]7.'Summary'of'two]factor'ANOVAs'for'the'effect'of'Treatment'and'Depth'on'stem'
and'filter'decomposition'and'Site'and'Depth'on'stem'and'filter'decomposition'(expressed'
as'first]order'rate'constants,'k).'den'df'indicates'the'denominator'degrees'of'freedom'and'
num'df'indicates'numerator'degrees'of'freedom. ................................................................................ 100'
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Table'4]1.'Average'decomposition'rates'expressed'as'first]order'rate'constants'(k;'day]1)'
for'each'litter'x'soil'origin'treatment'combination. ............................................................................. 153'
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Table'4]2.'Summary'of'the'two]factor'ANOVAs'for'the'effect'of'species]specific'litter'and'
soil'on'decomposition'constant'(K),'cumulative'C'mineralization,'and'N'mineralization.. 154'
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Table'4]3.'Soil'and'litter'%C,'%N,'and'C:N'mass'ratios'of'the'four'species'used'in'the'litter'
quality'and'soil'origin'incubation.''Same'letter'superscript'denotes'nonsignificant'
differences'according'to'Tukey'post'hoc'tests.'Values'are'means'±'SE....................................... 155'
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Table'4]4.'Average'decomposition'rates'expressed'as'first]order'rate'constants'(k;'day]1)'
for'each'litter'diversity'treatment. .............................................................................................................. 156'
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Table'4]5.'Summary'of'ANOVAs'for'the'effect'of'Treatment'on'decomposition'(K)'constant,'
cumulative'C'mineralization,'and'N'mineralization. ........................................................................... 156'
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Table'4]6.'Litter'C:N'mass'ratios,'%'lignin,'and'lignin:N'mass'ratios'of'the'four'species'used'
in'the'litter'diversity'incubation.''Same'letter'superscript'denotes'nonsignificant'
differences'according'to'Tukey'post'hoc'tests.'Values'are'means'±'SE....................................... 156'
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Table'A]1.'Models'of'Biomass'C'Stock.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 186'
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Table'A]2.'Models'of'Biomass'N'Stock.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 186'
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Table'A]3.'Models'of'Litter'C'Stock.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 186'
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Table'A]4.'Models'of'Litter'N'Stocks.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 187'
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Table'A]5.'Models'of'Litter'C:N'ratio.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 187'
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Table'A]6.'Models'of'Soil'C'Stock.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 188'
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Table'A]7.'Models'of'Soil'N'Stocks.''Model'in'bold'indicates'the'best]fit'model'based'on'
lowest'AIC'value. ................................................................................................................................................. 189'
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Table'A]8.''Models'of'Soil'C:N.''Model'in'bold'indicates'the'best]fit'model'based'on'lowest'
AIC'value. ................................................................................................................................................................ 190'
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Table'A]9.'Models'of'Ecosystem'C'Stock.''Model'in'bold'indicates'the'best]fit'model'based'
on'lowest'AIC'value............................................................................................................................................ 190'
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Table'A]10.'Models'of'Ecosystem'N'Stock.''Model'in'bold'indicates'the'best]fit'model'based'
on'lowest'AIC'value............................................................................................................................................ 190'
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Table'A]11.''Best]fit'model'summary'table'for'each'dependent'variable. ................................. 191'
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LIST'OF'FIGURES'
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Figure'1]1.'Interactions'between'plant'community'composition'(PCC),'plant'traits'and'soil'
microenvironment'influence'ecosystem'processes.''Plant'community'composition'effects'
on'C'and'N'cycling'are'mediated'though'plant'traits'directly'(plant'N'uptake)'and'indirectly'
(substrate'quality'and'soil'microenvironment'alteration).''Invasive'species'introduce'novel'
plant'traits'into'a'community'and'potentially'can'alter'ecosystem'function.''Arrows'
represent'pathways'of'influence'and'are'addressed'in'the'text........................................................23''
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Figure'2]1.''Regression'between'invasive'species'dominance'(percent'biomass'of'
community)'and'Shannon'Diversity'index'(adjusted'R2'='0.75,'p'<'0.001).................................52'
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Figure'2]2.''Regression'between'invasive'species'biomass'(cumulative'biomass'of'
Phragmites'australis,'Phalaris+arundinacea,'and+Typha'spp.)'and'site'nitrogen'use'efficiency'
(adjusted'R2'='0.10,'p'='0.08). ..........................................................................................................................53'
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Figure'2]3.'Regression'between'invasive'species'biomass'(cumulative'biomass'of'
Phragmites'australis,'Phalaris+arundinacea,'and+Typha'spp.)'and'total'biomass'(adjusted'R2'
='0.61,'p'<'0.001)....................................................................................................................................................54'
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Figure'2]4.'Regression'between'biomass'%'N'and'litter'C:N'ratio'(adjusted'R2'='0.32,'p'<'
0.001).''Biomass'%N'was'a'significant'predictor'in'the'best]fit'model'for'litter'C:N'ratios. 55'
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Figure'2]5.''Regression'between'invasive'species'biomass'(cumulative'biomass'of'
Phragmites'australis,'Phalaris+arundinacea,'and+Typha'spp.)'and'soil'C'stock'(adjusted'R'='
0.27,'p'<'0.001).'Invasive'species'biomass'was'a'significant'predictor'in'the'best]fit'model'
for'soil'C'stock. ........................................................................................................................................................56'
'
Figure'2]6.''Regression'between'invasive'species'biomass'(cumulative'biomass'of'
Phragmites'australis,'Phalaris+arundinacea'and+Typha'spp.)'and'ecosystem'C'stock'
(adjusted'R2'='0.35,'p'<'0.001).'Invasive'species'biomass'was'a'significant'predictor'in'the'
best]fit'model'for'ecosystem'C'stock.............................................................................................................57'
'
Figure'2]7.''Carbon'mineralization'rates'over'the'36]day'laboratory'incubation.''Repeated'
measures'ANOVA'showed'that'there'was'a'significant'3]way'interaction'between'species,'
temperature'and'time'(F2,494'='7.00,'p'='0.001).''Error'bars'represent'1'SE.............................58'
'
Figure'2]8.''Mean'cumulative'C'mineralization'over'the'36]day'laboratory'incubation.''The'
main'effects'of'species'(F2,8'='5.82,'p'='0.028)'and'temperature'(F2,47'='1673.30,'p'<'0.001)'

xii'

were'significant,'but'not'their'interaction.''Same'letter'superscript'denotes'nonsignificant'
differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE..................................59''
Figure'2]9.''Regression'between'soil'C:N'ratio'and'cumulative'C'mineralization'at'high'
(21°C;'adjusted'R2'='0.53,'p'<'0.001)'and'low'(7°C;'adjusted'R2'='0.40,'p'<'0.001)'
temperatures. ..........................................................................................................................................................60'
'
Figure'2]10.'Comparison'of'mean'Q10'values'among'soil'collected'from'monospecific'
stands'of'Phragmites+australis,'Phalaris+arundinacea,'and'Typha'spp.''The'effect'of'species'
was'marginally'significant'(F2,8'='3.46,'p'='0.082).''Error'bars'represent'1'SE.........................61''''
'
Figure'2]11.''Comparison'of'mean'net'N'mineralization'rates'among'soil'collected'from'
monospecific'stands'of'Phragmites+australis,'Phalaris+arundinacea,'and'Typha'spp.''The'
effect'of'species'was'significant'(F2,5'='22.32,'p'='0.003).''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE. ..61''
'
Figure'3]1.''Map'showing'the'location'of'the'two'monospecific'stands'of'Phragmites+
australis'at'Lake'Lansing'Park'(LLP1'and'LLP2),'Haslett,'MI. ............................................................88'''
'
Figure'3]2.''Map'showing'the'location'of'the'monospecific'stand'of'Phragmites+australis'in'
the'wetland'area'surrounding'Glasby'Lake'(Glasby),'Delton,'MI......................................................89'
'
Figure'3]3.''Water'table'position'at'Glasby'and'LLP1'from'July'to'October'of'2008.''Zero'
water'level'represents'the'soil'surface'with'positive'water'levels'indicating'flooding'
(standing'water)'and'negative'values'indicating'a'water'table'below'the'soil'surface. ...... 101'
'
Figure'3]4.''Water'table'position'at'Glasby,'LLP1,'and'LLP2'from'August'to'November'of'
2009.''Zero'water'level'represents'the'soil'surface'with'positive'water'levels'indicating'
flooding'(standing'water)'and'negative'values'indicating'a'water'table'below'the'soil'
surface...................................................................................................................................................................... 102'
'
Figure'3]5.''Water'table'position'at'Glasby,'LLP1,'and'LLP2'from'July'to'October'of'2010.''
Zero'water'level'represents'the'soil'surface'with'positive'water'levels'indicating'flooding'
(standing'water)'and'negative'values'indicating'a'water'table'below'the'soil'surface. ...... 103'
'
Figure'3]6.''Water'table'position'at'Glasby,'LLP1,'and'LLP2'for'2008'to'2010'(see'methods'
for'exact'time'periods).''Zero'water'level'represents'the'soil'surface'with'positive'water'
levels'indicating'flooding'(standing'water)'and'negative'values'indicating'a'water'table'
below'the'soil'surface.''Error'bars'represent'1'standard'deviation. ............................................ 104!
'
Figure'3]7.''Mean'light'levels'(PAR)'measured'directly'above'the'soil'surface'within'control'
(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'plots'
averaged'across'sites.''There'was'a'significant'treatment'effect'(F3,81'='109.95,'p'<'0.001).''
Same'letter'superscript'denotes'nonsignificant'differences'according'to'Tukey'post'hoc'
tests.''Error'bars'represent'1'SE................................................................................................................... 105''
xiii'

'
Figure'3]8.''Mean'manual'temperature'measurements'taken'at'6'soil'depths'(and'ambient)'
within'control'(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'
treatment'plots'averaged'across'sites.''There'was'a'significant'interaction'between'
treatment'and'depth'(F18,174'='2.07,'p'<'0.009).''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE.106''
'
Figure'3]9.''Daily'ambient'mean'temperature'from'July'to'October'2010'within'control'(C),'
biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'plots. ......... 107'
'
Figure'3]10.'Daily'soil'surface'mean'temperature'from'July'to'October'2010'within'control'
(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'plots.. 108'
'
Figure'3]11.'Daily'mean'temperature'at'2'cm'soil'depth'from'July'to'October'2010'within'
control'(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'
plots. ......................................................................................................................................................................... 109'
'
Figure'3]12'Daily'mean'temperature'at'10'cm'soil'depth'from'July'to'October'2010'within'
control'(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'
plots. ......................................................................................................................................................................... 110'
'
Figure'3]13.''Mean'Cl]'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'treatment'(F2,63'='17.34,'p'<'0.001)'on'Cl]'concentrations,'
but'not'depth'or'their'interaction.''Error'bars'represent'1'SE. ..................................................... '111'
'
Figure'3]14.''Mean'Na+'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'treatment'(F2,63'='4.93,'p'='0.01)'on'Na+'concentrations,'
but'not'depth'or'their'interaction.''Error'bars'represent'1'SE. ...................................................... 112''
'
Figure'3]15.''Mean'Mg2+'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'treatment'(F2,63'='3.29,'p'='0.043)'and'depth'(F13,63'='
9.20,'p'<'0.001)'on'Mg2+'concentrations,'but'not'their'interaction.''Error'bars'represent'1'
SE.'.............................................................................................................................................................................. 113'
'
Figure'3]16.''Mean'Ca2+'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'treatment'(F2,63'='7.54,'p'='0.001)'and'depth'(F13,63'='
5.44,'p'<'0.001)'on'Ca2+'concentrations,'but'not'their'interaction.''Error'bars'represent'1'
SE................................................................................................................................................................................ 114''
xiv'

'
Figure'3]17.''Mean'SO42]'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'depth'(F13,63'='4.48,'p'<'0.001)'on'SO42]'concentrations,'
but'not'treatment'or'their'interaction.''Error'bars'represent'1'SE............................................... 115''
'
Figure'3]18.''Mean'NO3]]N'concentrations'from'porewater'equilibrators'within'control'(C),'
biomass'removal'(BR),'and'litter'removal'(LR)'treatment'plots'averaged'across'sites.''
There'was'a'significant'effect'of'depth'(F13,63'='3.16,'p'='0.049)'and'treatment'on'NO3]'
(F13,63'='2.91,'p'='0.002)'concentrations,'but'not'their'interaction.''Error'bars'represent'1'
SE............................................................................................................................................................................... '116'
'
Figure'3]19.''Mean'net'N'mineralization'rates'among'soil'collected'within'monospecific'
stands'of'Phragmites+australis'at'Glasby,'LLP1,'and'LLP2.''The'effect'of'site'was'significant'
(F2,87'='65.57;'p'<'0.001).''Same'letter'superscript'denotes'nonsignificant'differences'
according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE. ...................................................... 117''
'
Figure'3]20.''Mean'net'nitrification'rates'among'soil'collected'within'monospecific'stands'
of'Phragmites+australis'at'Glasby,'LLP1,'and'LLP2.''The'effect'of'site'was'significant'(F2,87'='
1.29;'p'<'0.001).''Same'letter'superscript'denotes'nonsignificant'differences'according'to'
Tukey'post'hoc'tests.''Error'bars'represent'1'SE. ................................................................................. 117'''
'
Figure'3]21.''Regression'between'soil'%'moisture'and'net'N'mineralization'rates'(adjusted'
R2'='0.297,'p'<'0.001)........................................................................................................................................ 118'
'
Figure'3]22.''Regression'between'soil'%'moisture'and'net'N'mineralization'rates'(adjusted'
R2'='0.406,'p'<'0.001)........................................................................................................................................ 118'
'
Figure'3]23.''Regression'between'soil'%'moisture'and'net'N'mineralization'rates'(adjusted'
R2'='0.125,'p'<'0.001)........................................................................................................................................ 119'
'
Figure'3]24.''Mean'first'order'rate'constants'(k;'day]1)'for'stems'incubated'within'control'
(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'plots'over'
a'90'day'time'period'averaged'across'sites.''There'was'a'significant'effect'of'depth'(F1,44'='
6.43;'p'='0.014),'but'not'treatment'or'their'interaction.''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE.119'''''
'
Figure'3]25.''Mean'first'order'rate'constants'(k;'day]1)'for'filters'incubated'within'control'
(C),'biomass'removal'(BR),'litter'removal'(LR),'and'total'removal'(TR)'treatment'plots'over'
a'90'day'time'period'averaged'across'sites.''There'was'a'significant'effect'of'depth'(F1,44'='

xv'

6.43;'p'<'0.001),'but'not'treatment'or'their'interaction.''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE.'120''''
'
Figure'3]26.''Mean'first'order'rate'constants'(k;'day]1)'for'stems'incubated'at'Glasby'(GL),'
LLP1,'and'LLP2'sites'over'a'90'day'time'period.''There'was'a'significant'interaction'
between'site'and'depth'(F2,54'='5.12;'p'='0.009).''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE.120'''''
'
Figure'3]27.'Mean'first'order'rate'constants'(k;'day]1)'for'filters'incubated'at'Glasby'(GL),'
LLP1,'and'LLP2'sites'over'a'90'day'time'period.''There'was'a'significant'interaction'
between'site'and'depth'(F2,54'='10.33;'p'<'0.001).''Same'letter'superscript'denotes'
nonsignificant'differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE.121''''''''
'
Figure'3]28.''Mean'denitrification'rates'(N2O'production)'among'soil'collected'within'
monospecific'stands'of'Phragmites+australis'at'Glasby,'LLP1,'and'LLP2.''The'effect'of'site'
was'significant'(F2,27'='11.41;'p'<'0.001).''Same'letter'superscript'denotes'nonsignificant'
differences'according'to'Tukey'post'hoc'tests.''Error'bars'represent'1'SE............................... 121''
'
Figure'3]29.''Regression'between'nitrate'and'denitrification'rates'(N2O'
production)(adjusted'R2'='0.310,'p'<'0.001).......................................................................................... 122'
'
Figure'3]30.''Regression'between'soil'C:N'ratio'and'denitrification'rates'(N2O'production)'
(adjusted'R2'='0.252,'p'<'0.001)................................................................................................................... 122'
'
Figure'4]1.'Map'showing'the'location'of'the'monospecific'stands'of'Phragmites+australis+
(Phr),+Phalaris+arundinacea+(Pha),+Typha × glauca+(Typ),+and+Carex+lacustris'(Car)'in'the'
wetland'area'within'Lake'Lansing'Park'North,'Haslett,'MI. ............................................................. 146'
'
Figure'4]2.''Mean'cumulative'C'mineralization'over'the'68]day'litter'quality'and'soil'origin'
€
laboratory'incubation.''The'main'effects'of'species]specific'litter'(F3,80'='69.43,'p'<'0.001)'
and'soil'origin'(F3,80'='11.29,'p'<'0.001)'were'significant,'but'not'their'interaction.''Same'
letter'superscript'denotes'nonsignificant'differences'according'to'Tukey'post'hoc'tests.''
Error'bars'represent'1'SE................................................................................................................................ 157'
'
Figure'4]3.''Regression'between'soil'C:N'ratio'and'cumulative'C'mineralization'(all'
treatments)'(adjusted'R2'='0.003,'p'='0.423). ........................................................................................ 158'
'
Figure'4]4.''Regression'between'soil'C:N'ratio'and'cumulative'C'mineralization'(no'litter'
treatments'only)'(adjusted'R2'='0.077,'p'='0.105)............................................................................... 158'
'

xvi'

Figure'4]5.''Regression'between'soil'%N'ratio'and'cumulative'C'mineralization'(no'litter'
treatments'only)'(adjusted'R2'='0.192,'p'='0.018)............................................................................... 159'
'
Figure'4]6.''Regression'between'litter'C:N'ratio'and'cumulative'C'mineralization'(litter'
addition'treatments'only)'(adjusted'R2'='0.524,'p'<'0.001). ........................................................... 159'
'
Figure'4]7.''Regression'between'litter'C:N'ratio'and'day'1'C'mineralization'(Litter'addition'
treatments'only)'(adjusted'R2'='0.861,'p'<'0.001)............................................................................... 160'
'
Figure'4]8.''Mean'net'N'mineralization'over'the'68]day'litter'quality'and'soil'origin'
laboratory'incubation.''The'main'effects'of'species]specific'litter'(F3,100'='92.30,'p'<'0.001)'
and'soil'origin'(F12,100'='14.07,'p'<'0.001)'were'significant,'but'not'their'interaction.''Same'
letter'superscript'denotes'nonsignificant'differences'according'to'Tukey'post'hoc'tests.''
Error'bars'represent'1'SE................................................................................................................................ 161'
'
Figure'4]9.'Regression'between'litter'C:N'ratio'and'net'N'mineralization'(adjusted'R2'='
0.452,'p'<'0.001).................................................................................................................................................. 162'
'
Figure'4]10.''Mean'cumulative'C'mineralization'over'the'55]day'litter'diversity'laboratory'
incubation.''The'main'effect'of'litter'treatment'was'significant'(F14,90'='8.08,'p'<'0.001).''
Same'letter'superscript'denotes'nonsignificant'differences'according'to'Tukey'post'hoc'
tests.''Error'bars'represent'1'SE................................................................................................................... 163'
'
Figure'4]11.''Regression'between'litter'C:N'ratio'and'cumulative'C'mineralization'(adjusted'
R2'='0.131,'p'<'0.001)........................................................................................................................................ 164'
'
Figure'4]12.''Regression'between'litter'%lignin'and'cumulative'C'mineralization'(adjusted'
R2'='0.228,'p'<'0.001)........................................................................................................................................ 164'
'
Figure'4]13.''Regression'between'litter'lignin/N'ratio'and'cumulative'C'mineralization'
(adjusted'R2'='0.313,'p'<'0.001)................................................................................................................... 165'
'
Figure'4]14.'Regression'between'litter'species'diversity'and'cumulative'C'mineralization'
(adjusted'R2'='0.075,'p'='0.002)................................................................................................................... 165'
'
Figure'4]15.''Mean'net'N'mineralization'over'the'55]day'litter'diversity'laboratory'
incubation.''The'main'effect'of'litter'treatment'was'significant'(F15,96'='845.21,'p'<'0.001).''
Only'the'no'litter'treatment'was'significantly'different'from'the'other'treatment'
combinations.''Error'bars'represent'1'SE. ............................................................................................... 166'
!
!

xvii'

Chapter!1!
Introduction!
!
'
Carbon!and!Nitrogen!Cycling!in!Wetlands!
'
Human]induced'alteration'to'global'biogeochemical'cycles'is'creating'considerable'
public'and'scientific'interest'today.''Of'special'concern'are'the'anthropogenic'activities'that'
have'directly'and'indirectly'increased'the'amount'of'reactive'nitrogen'(N)'(NO3]'and'NH4+;'
Galloway'et'al.'2003)'entering'terrestrial'and'aquatic'ecosystems,'due'to:'(1)'increased'
cultivation'of'leguminous'crops'that'biologically'fix'un]reactive'N'(N2)'to'ammonium,'(2)'
combustion'of'fossil'fuels'resulting'in'the'creation'of'NOx'species,'and'(3)'the'use'of'large'
quantities'of'NH4+]based'fertilizers'to'increase'crop'yield'worldwide'(Vitousek'et'al.'1997;'
Driscoll'et'al.'2003;'Galloway'et'al.'2003).''These'inputs'have'contributed'to'elevated'levels'
of'reactive'N'that'result'in'major'ecological'and'human'health'problems,'such'as'
tropospheric'ozone'formation,'acid'rain,'high'ammonium]N'toxicity'to'fish,'carcinogenic'
effects'of'increased'nitrate'levels'in'drinking'water,'and'stimulation'of'pathogenic'microbes'
which'can'cause'public'health'risks'(Vitousek'et'al.'1997;'Driscoll'et'al.'2003;'Galloway'et'
al.'2003;'Zedler'2003).''Aquatic'ecosystems'are'particularly'sensitive'to'nutrient'loading,'
which'can'result'in'eutrophication,'algal'blooms,'high'biological'oxygen'demand,'and'the'
formation'of'dead'zones'(Livingston'2000).'
Carbon'cycling'also'has'been'significantly'impacted'by'human'activities,'such'as'the'
use'of'combustion'engines,'the'processing'of'natural'gas'and'crude'oil,'and'deforestation'
(Hoffert'et'al.'1998).''These'actions'have'resulted'in'rising'concentrations'of'CO2'and'CH4'

1'

in'the'atmosphere.''Both'CO2'and'CH4'are'greenhouse'gases'and'are'hypothesized'to'drive'
most'of'the'anthropogenic'climate'change'now'underway'(in'addition'to'N2O),'and,'
therefore,'understanding'how'they'cycle'through'the'environment'is'of'great'importance.''
While'the'majority'of'the'carbon'in'the'biosphere'is'stored'in'the'world’s'ocean,'primarily'
as'bicarbonate'(Schlesinger'1997),'there'has'been'substantial'interest'in'understanding'the'
dynamics'of'terrestrial'carbon'sources'and'sinks'because'they'are'potentially'very'active'
and'thus'can'have'significant'impacts'on'carbon'cycling.''Heimann'and'Reichstein'(2008)'
suggested'that'on'a'global'scale'terrestrial'ecosystems'will'provide'a'positive'feedback'to'
global'warming,'mainly'by'permafrost'thawing,'the'microbial'priming'effect,'and'the'
interaction'between'carbon'and'nitrogen'cycles,'though'the'magnitude'of'effects'is'less'
well'known.''Soils'are'the'largest'terrestrial'carbon'pool,'though'living'plants'(trees,'
grasses,'etc.)'are'also'a'significant'pool'of'terrestrial'carbon.''Although'forest'and'grassland'
soils'can'store'organic'matter'for'long'periods'of'time,'wetlands,'by'far,'store'the'largest'
amount'of'carbon'on'an'areal'basis,'storing'a'global'total'of'approximately'300'–'700'
billion'tons'of'carbon'(Bridgham'et'al.'2006),'with'the'majority'in'northern'peatlands.''
Wetlands'are'significant'sinks'of'carbon'due'to'their'high'productivity'and'anaerobic'
conditions'that'promote'slow'decomposition,'thus'resulting'in'the'buildup'of'organic'
matter.''Euliss'et'al.'(2006)'estimated'that'North'American'prairie'wetland'restoration'
alone'has'the'potential'to'sequester'378'Tg'of'carbon'over'a'10]year'time'period,'offsetting'
the'annual'fossil'fuel'carbon'emissions'in'North'America'by'2.4%.''
There'is'a'strong'coupling'between'C'and'N'cycling'(Schlesinger'2011).''This'strong'
coupling'occurs'for'two'main'reasons:'(1)'there'is'a'stoichiometric'requirement'of'C'and'N'

2'

for'most'organisms,'so'limitation'of'one'element'will'usually'limit'the'cycling'of'the'other'
(assimilatory'coupling)'and'(2)'the'metabolic'capabilities'of'many'microbes'allow'for'the'
catalysis'of'energy'releasing'reactions,'usually'by'means'of'changes'in'oxidation'states'of'C'
or'N'(dissimilatory'coupling)'(Burgin'et'al.'2011).''In'dissimilatory'reactions,'the'elements'
are'not'incorporated'into'the'biomass'of'the'organism'and'are'instead'released'directly'
back'into'the'environment.''The'coupling'of'C'and'N'cycling'can'have'consequences'to'the'
structure'and'function'of'many'ecosystems.''For'example,'in'a'laboratory'incubation'using'
soil'collected'from'an'old]growth'coniferous'soil,'Hart'et'al.'(1994)'found'a'strong'positive'
relationship'between'CO2'evolution'and'gross'N'mineralization.''Microbial'growth'
efficiency'declined'over'the'incubation'period'(456'days)'suggesting'the'use'of'lower'
quality'substrates'as'C'availability'declined.''Thomas'et'al.'(2010)'studied'the'effects'of'N'
deposition'on'northeastern'forests'and'found'that'N'deposition'increased'the'growth'of'the'
majority'of'study'species,'and'thus'increased'tree'C'storage.''In'wetlands,'one'of'the'best'
examples'of'the'tight'coupling'between'C'and'N'is'the'denitrification'process.''In'low'
oxygen'conditions,'denitrifiers'can'convert'NO3]'to'N2O'and'N2'by'a'series'of'redox'
reactions'that'use'NO3]'as'an'electron'acceptor'and'organic'carbon'as'an'electron'donor.''
This'is'one'of'several'metabolic'pathways'responsible'for'the'decomposition'of'organic'
matter'in'anoxic'conditions.'''''''''''
''Wetlands'are'usually'found'in'depressional'areas'on'the'landscape'and'as'a'result'
they'receive'large'amounts'of'water'from'surface'and'ground'water'inflow,'making'them'
vulnerable'to'flooding,'nutrient'loading,'and'other'types'of'disturbance'(Zedler'and'
Kercher'2004).''Wetlands'are'defined'as'ecosystems'on'the'interface'between'terrestrial'

3'

and'aquatic'habitats'(Mitsch'and'Gosselink'2000).''The'three'main'features'that'distinguish'
a'wetland'are:'(1)'a'zone'of'saturation'(at'the'soil'surface'or'within'the'rooting'zone)'for'at'
least'part'of'the'year,'(2)'unique'soil'characteristics'arising'from'saturation'(e.g.,'gleying)'
and'(3)'the'presence'of'hydrophytes'(plants'adapted'to'saturated'soil'conditions)'with'the'
exclusion'of'plants'intolerant'to'waterlogging'(Mitsch'and'Gosselink'2000).''While'
wetlands'provide'a'host'of'ecosystem'services'such'as'wildlife'habitat,'flood'control,'and'
shoreline'stabilization'(Zedler'2003),'one'of'the'main'services'provided'by'these'
ecosystems'is'the'enhancement'of'water'quality'via'the'retention'and'removal'of'excess'N'
(Saunders'and'Kalff'2001;'Zedler'2003;'Verhoeven'et'al.'2006).''Wetlands'have'played'
major'roles'of'improving'water'quality'in'a'number'of'climatic,'ecological,'and'land]use'
settings'(Zedler'2003).''Wetlands'retain'and'remove'N'through'several'physical'and'
biological'processes,'including'N'retention'via'plant'N'uptake'for'metabolic'processes,'
cation'exchange'in'organic]rich'soils,'and'longer]term'sedimentation'and'burial'(Reddy'
and'Delaune'2008).''Microbially]mediated'transformations'of'N'in'wetlands,'including'
mineralization,'nitrification,'and'denitrification,'are'particularly'important'because'these'
processes'result'in'the'conversion'of'reactive'N'to'less'reactive'species'(N2O'and'N2)'that'
are'emitted'to'the'atmosphere.'
Wetlands'furnish'ecosystem'services'disproportionately'to'their'area,'particularly'in'
the'case'of'water'quality'improvement'(Zedler'2003;'Verhoeven'et'al.'2006).''Nitrogen'
retention'and'removal'by'wetlands'has'received'particular'attention'in'North'America'and'
Europe'where'excessive'N'is'a'concern.''Wetlands'can'reduce'the'ecological'and'health'
risks'posed'by'excess'N'in'aquatic'ecosystems,'especially'in'areas'where'agriculture'or'
other'land'uses'create'runoff'of'N'originating'from'fertilizers'(Verhoeven'et'al.'2006).''
4'

Wetland'N'cycling'is'sensitive'to'changes'in'soil'temperature,'redox'status,'available'
nutrients,'and'pH'(Reddy'and'DeLaune'2008)'(Figure'1]1;'pathways'5,'6,'and'8).''Because'
of'their'role'as'landscape'sinks'for'nutrients'and'organic'matter,'along'with'having'periods'
of'drying'and'rewetting,'wetlands'as'known'as'biogeochemical'“hotspots”'for'N'(McClain'et'
al.'2003).''Wetlands'are'very'productive'ecosystems,'and'in'most'cases,'rates'of'
photosynthesis'(primary'production)'are'greater'than'decomposition'creating'organic'
matter'rich'soil'that'contains'nutrients'as'well'as'electron'donors'(carbon)'needed'for'
many'N'transformation'processes.''For'example,'nitrification,'the'microbially]mediated'
conversion'of'ammonium'to'nitrate,'needs'an'aerobic'environment'and'ammonium'to'
occur.''Conversely,'denitrification'requires'nitrate'as'the'oxidant,'labile'organic'carbon'as'
the'electron'donor,'and'an'anaerobic'environment.''These'contrasting'requirements'limit'
the'rate'of'these'N'cycling'processes'in'most'ecosystems,'but'wetlands'provide'aerobic'and'
anaerobic'conditions'that'vary'spatially'and/or'temporally,'which'can'greatly'increase'the'
rates'of'processes'like'denitrification.'(McClain'et'al.'2003;'Reddy'and'DeLaune'2008).'''
Despite'their'benefits'to'water'quality,'the'majority'of'the'wetlands'in'the'United'States'
have'been'drained'or'degraded,'often'for'agricultural'purposes'(Zedler'2003).''Over'the'
past'several'decades,'mitigation'and'conservation'programs'in'the'United'States'have'been'
established'to'protect'remaining'wetlands,'though'they'remain'vulnerable'to'perturbations'
such'as'changes'in'natural'hydrologic'flow'and'nutrient'loading'from'surrounding'land]
uses'(Saunders'and'Kalff'2001;'Zedler'2003;'Verhoeven'et'al.'2006).''In'the'Great'Lakes'
region,'an'area'dominated'by'wetlands,'water,'and'water]based'recreation,'increasing'
invasions'by'exotic'species'are'considered'to'be'one'of'the'most'critical'threats'to'
biodiversity'and'ecosystem'stability'(Zedler'and'Kercher'2004).'

5'

Wetlands'are'especially'vulnerable'to'biological'invasions'because'of'their'landscape'
setting'where'they'often'receive'inflows'of'water'and'propagules,'and'because'they'often'
are'periodically'disturbed'by'flooding'and'drying'events'(Zedler'and'Kercher'2004;'Magee'
and'Kentula'2005).''While'wetland'plants'can'be'considered'stress]tolerators'(Grime'2002)'
because'they'are'adapted'to'environments'that'are'highly'variable'(e.g.,'seasonally'
flooded),'humans'have'introduced'additional'disturbances,'such'as'nutrient'loading,'that'
native'species'are'not'adapted'to.''Nutrient'loading'usually'favors'species'that'respond'
positively'to'high'nutrient'availability'(Davis'et'al.'2000),'which'is'the'case'for'most'
wetland'invasive'plants.''Recent'research'has'shown'that'tall,'clonal'species'with'runner'
behavior'(i.e.,'species'with'long'spacers'between'ramets,'which'includes'most'wetland'
invasive'plant'species)'respond'to'nitrogen'addition'by'increasing'in'abundance,'while'
short,'clumping'species'(many'native'wetland'plant'species)'decreased'in'abundance'
(Gough'et'al.'2012).''This'may'be'one'of'the'main'mechanisms'for'the'invasibility'of'
wetlands.'''''
Wetland'plants'influence'wetland'soils'and'hydrology'through'their'structure,'life'
history,'degree'of'clonality,'root'characteristics,'and'quantity'of'litter'inputs'(Ehrenfeld'
2003)'(Figure'1]1;'pathways'2'and'3).''Plants'and'their'litter'influence'abiotic'factors'(e.g.,'
water'availability'and/or'soil'temperature),'thereby'indirectly'affecting'microbial'
decomposition'rates'and'soil'carbon'sequestration'(Eviner'and'Chapin'2003;'Euliss'et'al.'
2006;'Lal'2008).'For'example,'Fisk'and'Schmidt'(1995)'found'that'relationships'between'N'
mineralization,'soil'temperature,'and'water'in'alpine'tundra'communities'varied'among'
plant'communities.''It'is'possible'that'invasion'by'high]productivity'plant'species'that'
generate'low'quality'litter'could'increase'C'and'N'storage,'thereby'enhancing'an'ecosystem'

6'

service'provided'by'wetlands.''A'meta]analysis'of'94'experimental'studies'across'a'variety'
of'ecosystems'found'that'invasive'species'influence'C'and'N'cycling'by'increasing'C'stocks'
(root'and'shoot),'plant'N'concentration,'and'inorganic'N'pools'in'the'soil,'and,'although'this'
pattern'was'not'influenced'by'ecosystem,'there'was'variation'in'the'strength'of'effect'
among'plant'functional'types'(Liao'et'al.'2008).'''
As'mentioned'above,'wetland'hydrology'has'great'influence'on'the'structure'and'
function'of'wetlands'(Hamilton'2002;'Trebitz'et'al.'2005;'Sierszen'et'al.'2006).''Directly,'
flooding'decreases'the'oxygen'concentration'within'soil'or'sediment,'which'has'
implications'for'soil'respiration'and'decomposition'(van'der'Valk'1991;'Neckles'and'Neill'
1994).''The'reduction'of'available'oxygen'due'to'flooding,'and'therefore'a'reduction'in'
decomposition,'is'one'of'the'main'reason'wetlands'accumulate'organic'matter'in'their'soils'
or'sediments.'''Flooding'not'only'changes'ecosystem'processes'directly'(e.g.,'prolonged'soil'
anaerobiosis),'but'also'indirectly'through'influence'on'the'plant'community'composition.'''
Because'flooding'can'be'a'common'disturbance'in'wetlands,'many'studies'have'focused'on'
how'flooding'can'affect'wetland'plant'communities'(e.g.,'Hudon'2004;'Kercher'and'Zedler'
2004).''While'most'wetland'plants'can'survive'periods'of'inundation,'plant'species'vary'in'
their'tolerance'to'the'duration'and'depth'of'flooding'(Cronk'and'Fennessy'2001).''This'
variation'in'flood'tolerance'among'species'is'one'of'the'main'causes'for'differences'in'plant'
community'composition'among'wetlands'(Sharitz'and'Pennings'2006).''Flooding'causes'
multiple'challenges'for'plant'species:'(1)'oxygen'diffuses'10,000x'slower'in'water'than'in'
air,'thus'roots'are'oxygen'limited,'(2)'anaerobic'conditions'produce'toxic'substances'such'
as'Fe'(II),'H2S,'and'organic'acids'that'can'harm'plant'roots,'and'(3)'complete'submergence'
of'the'plant'will'lead'to'a'reduction'of'light,'CO2,'and'oxygen'to'the'shoots'(Cronk'and'
7'

Fennessy'2001).''Wetland'plants'have'multiple'adaptations'to'cope'with'flooding'stress,'
including'passively'or'actively'transporting'oxygen'from'the'shoots'to'the'roots'for'root'
respiration,'releasing'oxygen'from'the'surface'of'the'root'creating'an'oxic'environment'that'
protects'the'root'from'Fe'(II)'and'H2S,'and,'in'many'cases,'tall,'emergent'stature'that'
ensures'direct'interface'with'the'atmosphere'in'most'conditions.''The'effect'of'flooding'on'
wetland'plant'community'composition'can'then'influence'ecosystem'function'by'altering'
the'predominant'plant'traits'within'the'community.''
'
Invasive!Species!and!Plant!Functional!Traits!
'
The'human]caused'redistribution'of'species'has'recently'accelerated'with'the'
economic'globalization'of'human'society'(Theoharides'and'Dukes'2007).''Invasions'by'
exotic'species'are'considered'to'be'one'of'the'most'critical'threats'to'biodiversity'and'
ecosystem'stability'(Walker'and'Steffen'1997).''Invasive'species'threaten'ecosystem'
function'on'multiple'levels'resulting'in'economic'costs'and'ecological'damage.''The'cost'of'
damage,'control,'and'removal'of'invasive'species'reaches'approximately'$137'billion'
annually'for'the'United'States'(Pimentel'et'al.'2000,'2004).''The'resulting'effects'of'species'
redistribution'caused'by'the'introduction'of'exotic'species'on'ecosystem]level'processes'
are'largely'unknown.'While'a'small'percent'of'introduced'species'become'established,'with'
an'even'smaller'amount'becoming'invasive'(Williamson'and'Fitter'1996),'those'species'
that'invade'successfully'often'become'dominant'and'can'alter'community'structure'and'
composition'(Levine'et'al.'2002).''For'example,'garlic'mustard'(Alliaria+petiolata)'invasion'
into'North'American'woodlands'has'resulted'in'the'alteration'of'under]story'plant'
communities'(Meekins'and'McCarthy'2000;'Stinson'et'al.'2007).''Closer'examination'also'

8'

has'shown'that'garlic'mustard'may'change'the'tree'community'to'more'shade'tolerant'
species'whose'seedlings'can'withstand'the'intense'shading'created'by'garlic'mustard'
stands'(Stinson'et'al.'2007).''In'addition,'garlic'mustard'produces'allelopathic'chemicals'
that'inhibit'the'growth'other'plants,'potentially'via'inhibition'of'mycorrhizal'fungi'(Weir'
2007).'''
While'much'research'has'investigated'why'certain'plant'species'become'invasive'while'
others'do'not,'it'is'not'entirely'clear'what'mechanisms'are'responsible'for'invasion'success.''
Some'of'the'most'supported'hypotheses'include'the'enemy'release'hypothesis,'broader'
tolerance'hypothesis,'efficient'use'hypothesis,'hybrid'vigor'hypothesis,'and'allelopathy'
hypothesis'(Zedler'and'Kercher'2004),'though'none'can'explain'all'invasions.''There'is'
much'evidence'that'propagule'pressure'is'a'strong'determinant'of'invasion'success'
(Lockwood'et'al.'2005),'and'more'recent'theory'suggests'that'invasion'is'a'complex'process'
with'many'stages'including'transport,'introduction,'establishment,'and'spread'(Blackburn'
et'al.'2011).''The'spread'of'invasive'species'have'also'been'connected'to'economic'activity;'
Taylor'and'Irwin'(2004)'were'able'to'explain'75%'of'the'variation'in'the'number'of'exotic'
plants'in'the'50'states'with'a'population]economic'model'that'incorporated'human'
population'and'real'estate.''
There'are'also'contrasting'patterns'for'the'effect'of'invasive'species'on'species'
diversity.''On'a'global'scale'it'seems'clear'that'species'diversity'is'decreasing'as'a'result'of'
many'human'activities,'such'as'habitat'destruction,'over]hunting,'and'species'introductions'
(Kerr'and'Currie'1995).''On'a'local'scale'(study'sites'less'than'a'few'dozen'hectares)'
species'loss'seems'to'follow'the'general'global'pattern;'species'introductions'decrease'
species'richness'(Sax'and'Gaines'2003).''The'pattern'for'regional'scales'(between'global'

9'

and'local'scale)'is'quite'different,'as'there'seem'to'be'diversity'increases'associated'with'
species'introductions'(Sax'and'Gaines'2003).''This'contrasting'effect'of'introduced'species'
is'not'easily'explained,'though'the'regional'increase'is'likely'partially'caused'by'species'
redistribution'by'humans,'increasing'the'total'number'of'species'on'a'continental'scale,'
while'at'the'local'scale'invasive'species'are'known'to'competitively'exclude'most'other'
species'where'they'occur.''The'decrease'in'species'diversity'at'a'local'scale'is'also'more'
severe'in'anthropogenic'environments'(Sax'and'Gaines'2003).''Another'paradox'related'
with'scale'is'the'positive'association'found'between'natives'and'exotic'species'richness'at'
broad'scales'contrasted'with'the'negative'associations'at'fine'scales'(Fridley'et'al.'2007).''
These'paradoxes'show'our'incomplete'understanding'of'species'invasions'and'seem'to'
suggest'that'more'focused'studies'are'needed'to'resolve'these'dilemmas.''Regardless'of'the'
mechanism'of'these'patterns,'it'is'clear'that'invasive'species'negatively'impact'species'
diversity'on'global'and'local'scales.''
When'an'invasive'plant'becomes'locally'dominant,'it'can'directly'and'indirectly'impact'
the'invaded'community'(Figure'1]1).''Invasive'and'resident'species'likely'differ'in'key'plant'
traits'such'as'tissue'quality,'productivity'(above]'and'below]ground),'and'phenology.''
Ecosystem'processes'are'sensitive'to'the'identity'of'plant'species'that'comprise'community'
species'pools'(Eviner'and'Chapin'2003),'thus'invasions'into'natural'communities'can'alter'
ecosystem]level'processes'by'introducing'novel'plant'traits'that'influence'soil'
environments,'soil'microorganism'composition,'and/or'nutrient'cycling.''In'a'mixed'
deciduous'forest'in'New'York'it'was'shown'that'invasive'woody'species'accelerated'
decomposition'rates,'which'in'turn'resulted'in'increased'N'loss'from'litter'(Ashton'et'al.'
2005).''What'was'interesting'about'this'study'was'that'all'litter'in'the'invaded'sites'(exotic'

10'

and'native'species)'decomposed'faster'compared'to'the'non]invaded'sites.''This'showed'
that'species]specific'litter'decomposition'was'not'the'only'important'difference'between'
invaded'and'non]invaded'sites'and'that'invasive'species'indirectly'affected'ecosystem'
processes'(Ashton'et'al.'2005).'''
Variation'in'plant'traits'within'a'community'is'known'to'influence'many'aspects'of''
ecosystem'function'(Chapin'2003).''Biomass'accumulation'and'other'plant'traits'that'affect'
organic'matter'quality'can'directly'and'indirectly'influence'an'ecosystem’s'ability'to'store'
carbon'(C)'and'nitrogen'(N)'within'litter'and'soil'layers'(Ehrenfeld'2003).''Previous'work'
has'shown'that'plant'functional'group'diversity'had'strong'effects'on'total'plant'N,'plant'
productivity,'and'light'penetration'in'an'experimental'grassland'in'Minnesota'(Tilman'et'al.'
1997),'while'functional'group'composition'was'a'more'important'predictor'of'ecosystem]
level'processes'than'functional'group'richness'in'a'serpentine'grassland'in'California'
(Hooper'and'Vitousek'1997).''Plant'functional'traits'such'as'leaf'tissue'chemistry,'rooting'
depth,'and'canopy'structure'affect'ecosystem'productivity'and'C'and'N'cycling'(Tilman'et'
al.'1997;'Ehrenfeld'2003;'Eviner'and'Chapin'2003).''
Plant'functional'traits'are'useful'to'study'because'they'allow'us'to'simplify'complex'
and'seemingly'species]specific'controls'on'ecological/biogeochemical'processes'to'a'few'
plant'traits'of'dominant'influence'(Eviner'and'Chapin'2003;'McGill'et'al.'2006).''This'allows'
predictions'to'be'made'about'the'outcomes'of'ecological'phenomena,'such'as'invasion,'
succession,'or'competition,'with'some'confidence'given'knowledge'of'important'functional'
traits'of'the'invading'or'competing'species'(Westoby'and'Wright'2006).''For'example,'
Spartina+alterniflora'invasion'into'native'Phragmites+australis'and'Scirpus+mariqueter'
populations'in'China'caused'an'increase'in'net'primary'production'and'C'and'N'storage.'

11'

This'was,'in'part,'the'result'of'S.+alterniflora'having'a'longer'growing'season,'denser'
canopy,'and'greater'root'biomass'than'either'native'species'(Liao'et'al.'2007).''In'addition,'
Lythrum+salicaria'invasion'of'Typha+latifolia'stands'in'New'York'resulted'in'higher'soil'
organic'matter'(OM)'content'and'greater'N'mineralization'rates.''While'hydrology'was'a'
major'control'on'N'transformations,'L.+salicaria'total'biomass'was'more'than'double'that'of'
T.+latifolia,'which'increased'litter'inputs'and'resulted'in'higher'soil'OM'content'(Fickbohm'
and'Zhu'2006).''If'a'trait'is'found'to'strongly'affect'ecosystem'processes,'e.g.,'
decomposition,'then'predictions'can'be'made'about'the'magnitude'of'effect'on'that'process'
for'species'that'share'that'trait.''
Although'the'benefits'of'investigating'the'influential'functional'traits'affecting'
ecosystem'processes'have'been'made'clear'(Diaz'and'Cabido'2001;'Lavorel'and'Garnier'
2002;'Arndt'2006;'Schindler'and'Gessner'2009),'not'all'variation'in'ecosystem'function,'
such'as'C'and'N'mineralization,'can'be'completely'explained'by'a'few'functional'traits.''In'
some'cases,'species'identity'is'the'best'predictor'of'ecosystem'level'effects'(Wardle'et'al'
2003).''Therefore,'if'possible,'it'is'important'to'simplify'complex'plant'community'data'to'a'
few'key'traits'of'large'effect,'as'well'as'to'investigate'if'specific'dominant'species'are'
strongly'influencing'the'overall'ecosystem'function,'perhaps'by'novel'traits'not'shared'by'
the'rest'of'the'community.''Invasions'by'exotic'species'are'a'good'example'of'situations'
where'both'approaches'may'be'useful.''''''
Phragmites+australis'has'been'shown'to'reduce'the'availability'of'inorganic'N'in'
wetlands'and'increase'organic'N'retention'(Findlay'et'al.'2002)'compared'to'native'
Spartina'species,'likely'due'to'differences'in'litter'chemistry.''Orwin'et'al.'(2008)'
demonstrated'that'C'substrate'identity'can'influence'soil'chemistry,'microbial'metabolism,'

12'

and'soil'microbial'community'structure,'all'of'which'could'influence'ecosystem'processes'
such'as'decomposition'and'NPP'(through'effects'on'plant'available'nutrients).''Angeloni'et'
al.'(2006)'showed'that'invasion'by'Typha+ × glauca'into'a'Michigan'marsh'increased'soil'
organic'matter'and'altered'the'composition'of'the'bacterial'and'specifically'denitrifier'

€
communities,'which'could'have'been'influenced'by'the'higher'aboveground'biomass'of'T. ×
glauca'compared'to'the'invaded'community.''While'it'is'possible'that'plant'invasions'in'

€
temperate'wetlands'could'stimulate'the'short]term'uptake'of'N'through'increased'biomass'
production,'invasive'species'could'have'different'longer]term'impacts'on'N'
transformations'in'wetlands'through'more'complex'controls'on'soil'microenvironments'
and'substrate'quality.'''
'Phragmites+australis'(common'reed),'Phalaris+arundinacea'(reed'canarygrass),'and'
Typha × glauca+(hybrid'cattail)'are'some'of'the'most'successful'invasive'species'in'North'
American'wetlands'(Zedler'and'Kercher'2004).''Phragmites+australis'is'invading'wetlands'

€ throughout'the'United'States,'and'is'of'particular'concern'in'the'Midwest'states'such'as'
Michigan'(Marks'et'al.'1994).'''Phragmites+australis'is'a'high]biomass'invasive'(Windham'
and'Lathrop'1999;'Minchinton'and'Bertness'2003),'and'can'have'high'N'use'efficiency'and'
low'litter'quality'(Findlay'et'al.'2002).''In'Michigan'wetlands,'P.+australis'occurs'in'the'same'
wetland'zone'as'Typha+latifolia'and'is'still'in'the'process'of'aggressively'invading'into'sites'
where'it'has'colonized'(S.'Hamilton,'personal'communication).''Phragmites+australis'has'
been'shown'to'reduce'the'availability'of'inorganic'N'in'wetlands'(Windham'2001)'and'
increase'N'retention'(Findlay'et'al.'2002)'compared'to'Spartina'species,'likely'due'to'
differences'in'litter'chemistry.''Similar'comparisons'with'Typha+latifolia'have'yet'to'be'
made.'

13'

Phalaris+arundinacea'and'T.+ × glauca'are'similar'to'P.+australis'in'that'they'produce'
higher'biomass'compared'to'native'species,'spread'through'clonal'growth,'and'displace'

€
native'wetland'plant'communities'(Lavergne'and'Molofsky'2004;'Wetzel'and'van'de'Valk'
1998;'Hudon'2004).''Exotic'genotypes'of'P.+arundinacea'was'introduced'to'the'United'
States'ca.'1850,'though'native'populations'are'known'to'have'existed'prior'to'that'
introduction'(Lavergne'and'Molofsky'2004).''Invasive'genotypes'have'been'shown'to'come'
primarily'from'Europe'and'after'introduction'for'forage,'bioremediation,'and'erosion'
control,'invasive'genotypes'hybridized'with'the'less'aggressive'native'genotypes'(Lavergne'
and'Molofsky'2007).''Currently,'the'distribution'of'P.+arundinacea'includes'most'of'the'
northern'half'of'the'United'States.'Phalaris+arundinacea'is'extremely'phenotypically'plastic'
and'can'adjust'morphologically'to'match'abiotic'conditions'(Martina'2006),'which'has'been'
assumed'to'aid'it'when'invading'in'to'new'areas.''Typha' × glauca,'currently'distributed'
across'the'eastern'United'States,'is'a'hybrid'between'T.'latifolia'(native)'and'Typha+

€
angustifolia'(exotic)'that'is'very'aggressive'and'can'out]compete'the'native'cattail'when'
they'co]occur.'''Typha+angustifolia'is'native'to'Europe'but'the'date'of'introduction'to'the'
United'States'is'not'well'known,'though'it'was'likely'at'the'beginning'of'the'20th'century.'''
For'invasive'species'that'are'more'productive'(in'terms'of'biomass)'than'natives,'such'
as'P.+australis,'P.+arundinacea,'and'T.+ × glauca,'one'of+two'mechanisms'may'be'responsible:'
(1)'invasives'have'higher'nitrogen'use'efficiency'(NUE,'biomass'per'unit'N)'than'natives'or'

€
(2)'they'respond'to'nutrient'loading'more'than'natives.''While'it'is'widely'hypothesized'
that'the'latter'is'the'correct'mechanism'in'most'circumstances'(Zedler'and'Kercher'2004;'
Tyler'et'al.'2007),'invasive'species'can'still'invade'wetlands'at'low'nutrient'levels'(Green'
and'Galatowitsch'2002)'and'there'is'also'evidence'that'invasives'are'successful'because'of'

14'

greater'NUE'(Funk'and'Vitousek'2007),'at'least'in'low'resource'habitats.++A'thorough'
understanding'of'how'these'invasive'plants'are'influencing'C'and'N'cycling,'along'with'the'
controlling'factors,'will'help'to'predict'the'impacts'of'invasion.'While'there'has'been'some'
research'on'the'effects'of'invasive'species'in'wetlands'(e.g.,'Findlay'et'al.'2002;'Angeloni'et'
al.'2006;'Liao'et'al.'2007),'few'studies'have'directly'investigated'the'mechanisms'
responsible'for'ecosystem'process'changes'due'to'invasion'and'even'fewer'have'looked'at'
multiple'invasive'species'simultaneously.'''
'
Decomposition:!Abiotic!and!Biotic!Determinants!!!!!
'
Decomposition'is'an'essential'ecosystem'process'defined'as'the'physical'and'chemical'
breakdown'of'organic'matter'(Chapin'et'al.'2002).''During'decomposition,'organic'matter'is'
broken'down'into'its'chemical'components'releasing'CO2'to'the'atmosphere'and'nutrients'
to'the'soil.''Decomposition'consists'of'three'basic'processes:'leaching,'fragmentation,'and'
chemical'alteration'(Chapin'et'al.'2002).''Leaching'is'the'mobilization'of'labile'soluble'
materials'into'water,'such'as'sugars'and'amino'acids,'from'decomposing'OM.''In'a'litter'bag'
field'incubation'investigating'the'controls'on'decomposition'in'two'Mediterranean'
ecosystems,'it'was'found'that'leaching'was'an'important'phase'in'decomposition'that'
lasted'2]4'months'(Gallardo'and'Merino'1993).'Fragmentation'is'the'physical'breakdown'
of'large'detritus'mainly'by'soil'animals'(though'freeze]thaw'and'wet]dry'cycles'can'also'
fragment'organic'matter)'that'increases'surface'area'for'microbial'activity'and'can'be'a'
very'important'process'in'environments'where'soil'animals'thrive'(Verhoef'and'Brussaard'
1990).''Soil'animals'can'also'influence'the'magnitude'and'direction'of'the'effects'of'litter'
diversity'on'decomposition'(Hattenschwiler'and'Gasser'2005).''Chemical'alteration'mainly'

15'

occurs'by'the'action'of'microbial'activity'though'some'alteration'can'occur'spontaneously,'
such'as'when'exposed'to'UV'radiation'(Austin'and'Ballare'2010).'''
Microbes'(mostly'fungi'and'bacteria)'release'extracellular'enzymes'that'react'with'
organic'matter'resulting'in'the'breaking'of'chemical'bonds.''Ultimately,'through'microbial'
respiration,'organic'matter'is'used'as'an'energy'source'and'oxidized'to'CO2'(in'aerobic'
environments).''The'majority'of'soil'respiration'is'due'to'the'action'of'both'bacteria'and'
fungi,'though'aspects'of'how'they'influence'decomposition'can'differ'in'important'ways.''
Fungi'are'the'main'initial'decomposers'of'dead'plant'material'because'they'are'capable'of'
producing'enzymes'that'can'break'down'most'plant'compounds,'including'lignin'(Chapin'
et'al.'2002).''Though'they'are'the'dominant'decomposers'in'ecosystems'like'forests'
because'of'their'large'networks'of'hyphae,'they'are'poor'decomposers'in'low'oxygen'
environments'like'wetlands.''Conversely,'bacteria'can'survive'in'oxygen'poor'soils'(e.g.,'
wetlands)'and'are'responsible'for'a'myriad'of'chemical'transformations,'such'as'
nitrification,'denitrification,'and'methanogenesis'that'occur'in'low'oxygen'conditions,'
though'in'soils'that'have'drying]rewetting'cycles,'bacteria'are'not'nearly'as'dominant,'and'
in'some'cases'fungi'can'become'dominant'(Strickland'and'Rousk'2010).'
Many'factors'influence'microbial'biomass'and'activity'and'thus'decomposition'rates,'
including'temperature,'moisture,'oxygen'concentration,'and'organic'matter'quality'
(Wardle'1992).''Generally,'increasing'temperature'can'directly'enhance'decomposition'by'
promoting'microbial'activity'with'almost'zero'microbial'activity'at'very'low'temperatures.''
Reichstein'et'al.'(2000)'incubated'subalpine'soil'at'three'temperatures'(5,'15,'and'25°C)'
and'found'that'increasing'the'temperature'by'10'degrees'nearly'tripled'C'mineralization'
rates.''While'in'many'laboratory'incubations'the'effect'of'temperature'on'the'
16'

mineralization'of'soil'organic'carbon'is'obvious,'a'study'by'Giardina'and'Ryan'(2000)'
compiled'data'from'82'sites'and'five'continents'and'determined'that'decomposition'of'
organic'matter'found'in'forest'mineral'soils'is'not'controlled'by'temperature'limitations'to'
microbial'activity.''This'apparent'lack'of'a'temperature'effect'on'decomposition'may'
actually'be'due'to'multiple'environmental'constraints'on'carbon'mineralization,'which'
might'also'be'sensitive'to'global'warming'(Davidson'and'Janssens'2005).'''
Soil'moisture'is'needed'due'to'the'requirement'of'water'for'normal'biotic'activity,'
though'as'soil'moisture'increases'to'fully'saturated'conditions,'oxygen'diffusion'is'reduced'
leading'to'anoxic'conditions.''Oxygen'is'required'for'aerobic'respiration,'which'yields'more'
energy'gain'compared'to'anaerobic'respiration.''In'the'absence'of'oxygen,'NO3]'is'used'as'
an'electron'acceptor'(denitrification)'followed'by'Mn4+,'Fe3+,'SO42],'CO2,'and'finally'H+,'
with'the'order'dictated'by'the'energy'efficiency'of'the'various'electron'acceptors'(more'
energy'is'gained'by'using'NO3]'as'an'electron'acceptor'compared'to'Mn4+)''(Reddy'and'
Delaune'2008).''Because'more'energy'is'gained'during'aerobic'respiration'versus'
anaerobic'respiration,'low'oxygen'concentrations'usually'results'in'low'decomposition'
rates,'though'anaerobic'respiration'using'NO3]'can'be'almost'as'efficient.''Oxygen'
availability'can'also'influence'humic'acid'formation;'Ramunni'et'al.'(1987)'found'that'the'
formation'of'humic'acids'during'decomposition'increased'in'the'presence'of'oxygen.'
''Finally,'organic'matter'quality'can'be'a'major'control'on'decomposition'rates.''
Organic'matter'quality'is'dependent'on'its'chemical'composition,'including'size'of'
molecules,'type'of'chemical'bonds,'regularity'of'structures,'toxicity,'and'nutrient'
concentration'(Chapin'et'al.'2002).''Lignin'is'very'recalcitrant'(hard'to'decompose)'because'

17'

it'is'a'large'phenolic'compound'with'a'very'irregular'structure,'making'enzymatic'
degradation'difficult.''Consequently,'plant'material'with'high'concentrations'of'lignin'
decomposes'slower'than'material'with'low'lignin'concentrations'(Melillo'et'al.'1982).''
Organic'matter'C:N'ratios'or'lignin:N'ratios'have'a'negative'relationship'with'
decomposition'rates'and'are'regularly'used'as'metrics'of'substrate'quality'(lability)'in'the'
literature.''In'a'study'of'seven'canopy'species'from'a'subtropical'evergreen'forest'in'Japan,'
Xu'and'Hirata'(2005)'found'decomposition'rates'were'strongly'controlled'by'N'and'lignin'
content,'as'well'as'C:N'and'lignin:N'ratios.'In'a'different'study'that'spanned'10'years,'21'
sites,'and'seven'biomes,'Parton'et'al.'(2007)'found'that'N'release'during'decomposition'
was'mainly'controlled'by'initial'N'concentrations,'i.e.,'litter'with'high'C:N'ratios'(low'N'
content)'released'less'N'over'the'incubation'period'than'litter'with'low'C:N'ratios'(high'N'
content).''They'also'found'that'net'N'release'started'when'litter'C:N'ratios'fell'below'about'
40'(range'of'31]48).'
Besides'the'four'major'determinants'of'decomposition'described'above,'litter'diversity'
can'have'profound'effects'on'decomposition'rates,'though'the'relationship'between'litter'
diversity'and'decomposition'can'be'positive,'negative,'or'neutral'(Gessner'et'al.'2010).''
Blair'et'al.'(1990)'used'the'leaf'litter'from'three'common'woody'species'(Acer+rubrum,'
Cornus+florida,+and'Quercus+prinus)'to'test'the'effects'of'single]'versus'mixed]species'litter'
bags'on'decomposition'and'found'that'mixed]species'litter'bags'had'greater'decomposition'
rates'than'single]species'litter'bags,'but'the'effects'of'the'mixed]species'litter'bags'could'
not'be'predicted'from'the'single]species'litter'bags.''They'hypothesized'that'the'difference'
between'mixed]'and'single]species'litter'decomposition'was'explained'by'changes'in'the'
decomposer'community'(Blair'et'al.'1990).''In'a'similar'experiment'performed'to'

18'

determine'if'enhanced'decomposition'due'to'increased'litter'diversity'was'caused'by'litter'
species'composition'or'alteration'to'the'microenvironment,'it'was'found'that'there'was'
more'support'for'changes'to'the'microenvironment'(physical'factors'and'decomposer'
community)'than'for'litter'species'composition'(Hector'et'al.'2000).''Litter'diversity'effects'
on'decomposition'may'be'specifically'important'in'plant'invasions'because,'initially,'the'
addition'of'an'invasive'species'may'increase'litter'diversity,'but'later'in'the'invasion,'if'the'
invasive'species'forms'a'monospecific'stand,'litter'diversity'would'be'lower.''''
Wetlands'are'highly'productive'ecosystems'that'undergo'periodic'flooding'events;'
therefore,'productivity'is'usually'greater'than'decomposition'causing'the'accumulation'of'
organic'matter'in'wetland'soils'(Mitsch'and'Gosselink'2000).''Because'of'the'low'oxygen'
levels'in'the'soil,'fungi'and'soil'animals'cannot'survive'and'therefore'bacteria'mediate'the'
majority'of'decomposition.''In'flooded'soils,'the'absence'of'both'fungi'and'soil'animals'
(Anderson'and'Smith'2000)'slows'decomposition'due'to'the'positive'effects'of'
fragmentation'by'soil'animals'and'lignin'breakdown'by'fungi'(Hattenschwiler'et'al.'2005).''
As'discussed'above,'wetlands'are'considered'biogeochemical'“hotspots”'because'of'the'
landscape'sink'nature'of'wetlands'combined'with'wetting'and'drying'events'(McClain'et'al.'
2003).''These'“hotspots”'are'created'by'the'diversity'of'redox'reactions'that'often'occur'in'
close'proximity'to'each'other'due'to'the'micro]gradients'of'oxygen'concentrations'in'soil'
pore'space'(Burgin'et'al.'2011),'which'often'vary'spatially'and'temporally.''This'makes'
wetlands'the'site'of'multiple'transformation'pathways'for'many'elements,'including'C,'N,'
Fe,'P,'S,'and'Hg.'''
Wetland'plants'can'influence'all'of'the'major'determinants'of'decomposition'discussed'
above,'including'temperature'(soil'shading;'Eviner'and'Chapin'2003),'soil'moisture'

19'

(evapotranspiration;'Goulden'et'al.'2007),'oxygen'availability'(radial'oxygen'loss;'Soukup'
et'al.'2007)'and'organic'matter'quality'(litter'quality;'Quested'et'al.'2007).''Therefore,'plant'
community'composition'is'an'important'factor'to'consider'when'attempting'to'understand'
elemental'cycling'in'wetlands.''Additionally,'plants'can'“condition”'soil'by'influencing'the'
soil'microbial'community,'soil'nutrient'availability,'priming'effect'(Fontaine'et'al.'2003),'or'
by'all'of'the'above'effects.''This'conditioning'can'then'feed'back'to'alter'the'decomposition'
of'plant'OM'inputs,'such'as'litter.''The'“home]field'advantage”'phenomenon,'described'by'
Gholz'et'al.'(2000)'and'Ayres'et'al.'(2009),'is'an'example'of'soil'conditioning'where'soil'
microbes'become'accustomed'to'OM'inputs'by'the'dominant'plant'species,'resulting'in'the'
OM'inputs'from'that'plant'species'decomposing'faster'(Strickland'et'al.'2009).''A'more'
complete'understanding'of'plant'effects'on'C'and'N'cycling'in'wetlands'is'required'to'be'
able'to'predict'the'effects'of'plant'invasion'on'biogeochemical'cycling.'''''
'''''
Research!Objectives!
'
The'broad'goal'of'my'dissertation'research'was'to'quantify'the'ecosystem'
consequences'of'invasive'plant'species'in'temperate'wetlands,'focusing'on'Phragmites+
australis,+Phalaris+arundinacea,'and'Typha+ × glauca.'The'first'part'of'my'research'(Chapter'
2)'characterizes'the'spatial'variability'in'C'and'N'storage'and'organic'matter'quality'in'24'

€
wetlands'in'south]central'Michigan.''In'Chapter'3,'I'investigate'the'mechanisms'by'which'P.+
australis'influences'C'and'N'cycling'in'three'wetlands'in'central'Michigan.''In'Chapter'4,'to'
understand'the'effects'of'litter'quality,'soil'origin,'and'plant'diversity'on'C'and'N'
mineralization,'I'performed'two'laboratory'incubations'using'litter'and'soil'collected'from'
monospecific'stands'of'invasive'species.''Together,'these'approaches'allowed'me'to'test'the'

20'

following'hypotheses!regarding'direct'and'indirect'effects'of'invasive'plants'on'plant'
community'composition'and'ecosystem'processes'in'wetlands:''
+
Hypothesis+1+(Chapter'2):'Invasion'into'wetlands'by'plant'species'that'typically'form'
monospecfic'stands'reduce'species'richness'and'evenness,'and'therefore'there'will'be'a'
negative'relationship'between'the'invasive'species'dominance'and'Shannon'diversity.''
+
Hypothesis+2+(Chapter'2):''Invasive'plants'have'higher'nitrogen]use'efficiency'(NUE)'
than'natives,'leading'to'higher'biomass'per'unit'of'available'N'as'well'as'lower'N'content'of'
biomass'and'litter'(Figure'1]1;'pathway'1,'10).''
+
Hypothesis+3+(Chapter'2):''The'lower'quality'(lower'N'content,'higher'C:N'ratio)'of'litter'
from'the'invasive'species'results'in'lower'rates'of'decomposition,'increasing'rates'of'
organic'matter'storage'in'invaded'wetlands'(Figure'1]1;'pathway'8,'9).'
'
Hypothesis+4'(Chapter'2'and'4):'Variation'among'invasive'species'effects'on'C'and'N'
mineralization'rates'can'be'attributed'to'differences'in'plant'traits'among'species,'
specifically'litter'quality'(Figure'1]1;'pathway'3,'8,'9).'''''
+
Hypothesis+5'(Chapter'3):''Invasive'plants'(specifically,'Phragmites+australis)'influence'
C'and'N'cycling'directly'by'affecting'plant'N'uptake'(Figure'1]1;'pathways'1,'4'and'1,'5,'9)'
and'indirectly'by'affecting'soil'climate'(Figure'1]1;'pathways'2,'6,'9'and'3,'7,6,'9)'and'the'
quality'and'quantity'of'organic'matter'inputs'(Figure'1]1;'pathway'3,'8,'9).'
'
21'

Hypothesis'6'(Chapter'4):'C'and'N'mineralization'rates'depend'not'only'on'the'species]
specific'quality'of'the'litter'(hypothesis'4),'but'also'on'the'conditioning'of'the'soil'by'the'
dominant'species.''The'soil'conditioning'effect'can'be'due'to'the'priming'effect'(Figure'1]1;'
pathway'3,8,9),'differences'in'soil'microbial'community'(Figure'1]1;'pathway'9),'or'soil'
nutrient'availability'(Figure'1]1;'pathways'1,5,9'and'8,9).''
+
Hypothesis+7+(Chapter'4):''Mixtures'of'litter'from'different'plant'species'have'higher'
decomposition'rates'compared'to'litter'from'monospecific'stands'due'to'higher'substrate'
diversity'(Fig.'1]1;'pathway'3,8,9).''Hence,'invasive'species'decrease'decomposition'rates'
by'reducing'species'(and'hence'litter)'diversity.''

22'

!
Alters PCC, including
dominance

Introduced plant traits

Nitrogen
Use
Efficiency/
Productivity

Leaf Area
1
2 Index/ Biomass
Production
Litter N concentration

Plant N Uptake
N Retention 4

C and N Storage and
Cycling

Determines plant trait
composition and dominance

Plant Traits

3

Invasive Species
Introduction

Plant Community Composition (PCC)

Litter Inputs

7
ading
oil Sh

10
ubs
tr

Ns

3

Pathway Effects
Direct
Indirect

Soil Microenvironment
S
ate
8
ava
ilab
6 Soil
5
le fo
temperature
r mi
crob
es
9
Microbial Community/
Metabolism
C and N cycling rates

Substrate Quality,
Quantity and Diversity
Amount, quality and
diversity of OM
available for
decomposition

Figure 1-1. Interactions between plant community composition (PCC), plant traits and soil microenvironment
influence ecosystem processes. Plant community composition effects on C and N cycling are mediated
though plant traits directly (plant N uptake) and indirectly (substrate quality and soil microenvironment
alteration). Invasive species introduce novel plant traits into a community and potentially can alter ecosystem
function. Arrows represent pathways of influence and are addressed in the text.

23!

Chapter(2(
Organic(Matter(Accumulation(and(Quality(in(Michigan(Wetlands:(Consequences(of(
Invasive(Plants(
!
Brief(Rationale(
!
Wetlands!provide!a!number!of!valuable!ecosystem!services,!such!as!wildlife!habitat,!
flood!control,!shoreline!stabilization,!and!C!and!N!retention!and!storage!(Zedler!2003).!!
There!has!been!increasing!interest!in!understanding!the!spatial!and!temporal!pattern!of!C!
dynamics!in!different!ecosystems!due!to!the!concern!of!increasing!greenhouse!gas!(CO2!and!
CH4)!concentrations!in!the!atmosphere!(Smith!et!al.!2012).!!Globally,!wetlands!only!cover!
2J6%!of!the!land!area,!but!store!14.5%!of!the!terrestrial!C!stocks!(Post!et!al.!1982)!mostly!
due!to!their!high!productivity!and!low!decomposition!rates!caused!by!prominent!anaerobic!
conditions!(Reddy!and!DeLaune!2008).!!While!most!of!the!global!wetland!C!stocks!are!
associated!with!peatlands!in!northern!latitudes!(Roulet!2000),!temperate!wetlands!can!also!
be!important!landscape!sinks!for!both!C!and!N!(Euliss!et!al.!2006).!!The!role!wetlands!play!
in!N!retention!has!been!known!for!a!while,!though!the!exact!mechanisms!and!processes!
associated!with!N!cycling!in!wetlands!is!still!an!active!area!of!study!(Chapman!et!al.!2006).!!
Wetlands!are!known!as!biogeochemical!“hotspots”!because!of!the!allochthonous!inputs!of!
carbon!substrates!and!nutrients,!along!with!a!fluctuating!hydrology!causing!temporal!
variation!to!the!redox!status!of!the!sediment,!which!creates!the!ideal!environment!for!N!
processes!such!as!denitrification!(McClain!et!al.!2003).!!Wetlands!are!therefore!known!to!
both!store!N!and!lose!N!through!denitrification.!!!!!!!!!
!

For!some!of!the!same!reasons!that!make!wetlands!biogeochemical!hotspots,!

wetlands!also!can!be!one!of!the!most!invaded!ecosystems,!given!that!they!serve!as!sinks!for!
invasive!species!propagules!(carried!by!inflows!of!surface!water),!nutrients,!and!

24!

disturbance!(Zedler!and!Kercher!2004).!!Disturbance!(Eschtruth!and!Battles!2009),!
propragule!pressure!(Lockwood!et!al.!2005),!and!nutrient!enrichment!(Davis!et!al.!2000)!
have!all!been!shown!to!increase!the!colonization!and!establishment!of!invasive!species,!
making!wetlands!very!susceptible!to!invasion.!!Additionally,!many!of!the!species!that!
invade!wetlands!are!clonal!species!that!can!form!monospecific!stands,!which!reduces!
diversity!and!species!interactions.!!Invasive!species!in!temperate!wetlands!are!usually!high!
biomass!producers!associated!with!thick!litter!layers.!!Because!these!species!usually!
produce!more!biomass!than!native!species,!they!either!have!higher!nitrogen!use!
efficiencies!(NUE:!the!amount!of!biomass!produced!per!unit!N)!or!are!able!to!access!a!
larger!pool!of!N!compared!to!natives.!!Organic!matter!buildup!beneath!monospecific!stands!
of!aggressive!wetland!invaders,!such!as!Typha! × glauca,!has!been!documented!(Ehrenfeld!
2003;!Angeloni!et!al.!2006),!though!the!pattern!across!different!wetland!types!has!not!been!

€
evaluated.!!With!the!prevalence!of!invasion!in!temperate!wetlands!it!is!important!to!
understand!the!effect!of!invasion!on!wetland!processes!such!as!C!and!N!storage!and!organic!
matter!quality.!!It!is!possible!that!invasion!by!high!biomass!invasive!species!could!increase!
wetland!C!and!N!storage!and,!therefore,!could!be!a!positive!outcome!of!invasion.!!
( While!there!has!been!some!research!on!the!effects!of!invasive!species!in!wetlands!
(e.g.,!Findlay!et!al.!2002;!Angeloni!et!al.!2006;!Liao!et!al.!2007),!few!studies!have!directly!
characterized!the!spatial!variability!in!C!and!N!storage!and!organic!matter!quality!and!even!
fewer!have!looked!at!multiple!invasive!species!simultaneously.!!Additionally,!though!these!
species!likely!have!cumulative!effects,!they!can!also!differ!in!plant!traits,!e.g.,!litter!quality,!
and!therefore!it!is!important!to!understand!the!differences!among!invasive!species.!!The!
broad!goal!of!this!chapter!is!to!quantify!the!consequences!of!invasive!species!in!temperate!

25!

wetlands!on!C!and!N!storage!and!organic!matter!quality.!!!In!the!first!part!of!this!chapter,!I!
quantified!the!effects!of!invasive!species!on!plant!community!composition,!litter!and!soil!C!
and!N!stocks,!and!OM!quality.!!In!the!second!part!of!this!chapter,!I!used!two!soil!assays!to!
determine!differences!in!C!and!N!mineralization!rates!from!soil!collected!from!
monospecific!stands!of!the!most!dominant!invasive!species.!
*
Objectives,(Hypotheses,(and(Predictions(
!
Objective)1:!To!determine!the!cumulative!effect!of!invasive!wetland!plants!on!species!
diversity,!C!and!N!storage,!and!organic!matter!quality.!
!
Hypothesis)1:!!Invasion!into!wetlands!by!species!that!can!form!monospecfic!stands!reduces!
species!richness!and!evenness.!!
!
Prediction!1.1:!There!will!be!a!negative!relationship!between!invasive!species!
dominance!and!Shannon!diversity.!!
)
Hypothesis)2:!Invasive!plant!species!have!higher!nitrogenJuse!efficiency!(NUE)!than!native!
species,!leading!to!lower!N!content!of!their!biomass!and!litter.!
!
Prediction!2.1:!There!will!be!a!positive!correlation!between!the!degree!of!invasion!
(total!biomass!of!invasive!species)!and!the!overall!plant!community!NUE.!
!
Prediction!2.2:!Degree!of!invasion!will!be!positively!correlated!with!organic!matter!
C:N!ratios!(litter!and!soil).!
26!

*
Hypothesis)3:!!Invasive!plant!species!have!litter!with!higher!C:N!ratios!than!native!species’!
litter,!leading!to!increased!organic!matter!storage!from!slower!rates!of!decomposition.!
!
Prediction!3.1:!!There!will!be!a!positive!correlation!between!the!degree!of!invasion!
and!litter!C!and!N!stocks,!soil!C!and!N!stocks,!and!total!ecosystem!C!and!N!stocks.!
!
Prediction!3.2:!!Based!on!hypothesized!higher!NUE!of!invasives,!litter,!soil,!and!
ecosystem!N!stocks!could!either!decrease!or!increase!with!the!degree!on!invasion.!!
There!is!uncertainty!because!while!the!overall!decrease!in!tissue!N!content!should!
decrease!N!stocks,!the!decreased!N!content!could!also!lower!the!quality!of!the!OM!
and!therefore!lead!to!low!decomposition!rates!and!N!buildup.!!
!
Objective)2:!!For!objective!1,!I!tested!the!cumulative!effects!invasive!species!have!on!C!and!
N!stocks!and!OM!quality,!though!there!was!evidence!for!variation!among!invasive!species!
in!key!plant!traits!that!could!influence!the!speciesJspecific!magnitude!of!effect.!!This!
variation!was!examined!through!the!use!of!two!assays!to!determine!differences!in!C!and!N!
mineralization!rates!from!soil!collected!from!monospecific!stands!of!the!most!dominant!
invasive!species.!!An!additional!objective!was!to!be!able!to!link!the!variation!among!
invasive!species!to!plant!traits,!such!as!litter!quality.!
!
Hypothesis)4:!The!quality!(C:N!ratio)!of!soil!collected!within!monospecific!stands!of!the!
most!dominant!invasive!species!from!the!wetland!survey!will!influence!C!and!N!

27!

mineralization!rates,!and!the!variation!in!soil!quality!will!mainly!be!due!to!litter!quality!
differences!among!species.!!!
!
Prediction!4.1:!!The!will!be!a!negative!relationship!between!soil!C:N!ratios!and!C!and!
N!mineralization!rates.!!
!
Prediction!4.2:!!Soil!collected!from!monospecific!stands!of!the!species!with!the!most!
recalcitrant!litter!(high!C:N!ratios)!will!have!the!highest!soil!C:N!ratios,!and!
therefore!the!lowest!mineralization!rates.!
!
(
Methods(
!
Study*sites*and*sampling*for*wetland*survey*!
!
This!study!was!conducted!near!the!W.K.!Kellogg!Biological!Station!(KBS)!on!
Michigan!State!University!property!in!southwestern!Michigan,!and!at!Lake!Lansing!Park!
(LLP)!in!central!Michigan!during!peak!biomass!growth!(late!June!to!early!August).!The!
region!around!KBS!lies!on!a!glacial!landscape!and!has!abundant!wetland!cover!(approx.!
10%),!with!low!levels!of!residential!development!in!a!landscape!dominated!by!forests,!rowJ
crop!agricultural!fields,!and!abandoned!fields.!!The!wetlands!of!Lake!Lansing!Park!are!
embedded!in!a!mosaic!of!woodlots!and!residential!areas!and!are!contiguous!with!the!lake!
system.!!!
In!the!summer!of!2007,!23!wetlands!near!KBS!and!one!wetland!at!LLP!were!sampled!
(for!GPS!coordinates!of!each!site!see!Table!2J1).!!Wetland!sampling!sites!were!chosen!to!
span!the!diversity!of!wetlands!around!KBS!that!support!emergent!vegetation!including!the!

28!

focal!invasive!species,!along!with!an!additional!depressional!wetland!at!LLP!dominated!by!
Phragmites*australis.!!Wetlands!were!classified!based!on!their!hydrogeomorphic!setting!as!
well!as!the!dominant!water!source,!estimated!using!dissolved!magnesium!(Mg2+)!in!the!
wetland!surface!water!as!an!indicator!of!precipitation!versus!groundwater!dominance;!
higher!Mg2+!concentrations!indicated!higher!groundwater!contribution!to!standing!water!
(Stauffer!1985,!Whitmire!and!Hamilton!2008).!Categories!include!depressional!
(precipitation!dominated),!intermediate!(in!between!groundwater!and!precipitation!
dominance),!groundwater!dominated,!and!lakeside.!!Lakeside!wetlands!were!given!a!
unique!classification!due!to!the!overriding!effect!an!adjacent!lake!has!on!the!physical!and!
chemical!wetland!environment!(HGM!classification;!Brinson!1993).!!These!wetlands!were!
relatively!small,!usually!with!a!total!surface!area!of!less!than!one!hectare.!The!majority!of!
the!study!sites!had!relatively!pure!stands!of!P.*australis,*Phalaris*arundinacea,!and*Typha*
spp.!(hereafter!Phragmites,!Phalaris,!Typha,!respectively),!or!mixtures!of!relatively!pure!
stands!of!these!species.!The!most!common!native,!nonJinvasive!graminoid!species!at!these!
sites!included!sedges!(Carex!spp.),!rushes!(Juncus!spp.),!and!spikeJrushes!(Eleocharis!spp.).!!
Other!common!wetland!species!found!at!these!sites!included!buttonbush!(Cephalanthus*
occidentalis),!pickerelweed!(Pontederia*cordata),!spatterdock!(Nuphar*advena),!and!
smartweed!(Polygonum!spp.).!!
!A!randomly!placed!linear!transect!was!set!up!in!the!emergent!vegetation!zone!at!
each!site.!!Six!1.0!x!0.5!m!(0.5!m2)!quadrats!were!established!along!each!transect!for!
vegetation,!litter,!and!soil!sampling.!!The!quadrats!were!randomly!placed!(1J10!m!distance!
between!quadrats)!along!the!transect!using!a!random!number!table.!!In!each!quadrat,!all!

29!

plant!species!that!had!developed!past!the!seedling!stage!were!identified!and!percent!cover!
was!estimated!for!each.!!SpeciesJspecific!aboveground!biomass!was!clipped!at!the!soil!
surface,!dried!at!65°C!for!48!hours,!and!weighed!on!a!topJloading!balance.!!Litter!depth!was!
measured!and!a!known!area!of!litter!(629!cm2)!was!removed!from!the!soil!surface,!
avoiding!mostly!decomposed!material!beneath!the!relatively!fresh!litter!layer.!!Litter!
samples!were!collected,!dried,!and!weighed!in!the!same!manner!as!biomass!samples.!!
Surface!soil!was!sampled!to!10!cm!depth!using!a!soil!corer!(246!cm3)!and!samples!were!
transported!to!the!lab!on!ice!and!frozen!until!processed.!!For!processing,!soils!were!thawed,!
sieved!(4!mm),!subJsampled!for!bulk!density!and!gravimetric!water!content!(GWC)!
determination,!and!then!dried!to!a!constant!mass!at!80°C.!!!
!
Carbon*and*nitrogen*analysis*
!

Dried!aboveground!biomass!and!litter!samples!were!ground!and!homogenized!using!

a!cyclone!sample!mill!(Udy!Corporation,!Fort!Collins,!CO)!and!dried!soil!samples!were!
ground!using!a!mortar!and!pestle.!!Percent!C!and!N!were!measured!for!aboveground!
biomass,!litter,!and!soil!using!a!Costech!Elemental!Combustion!System!4010!(Costech!
Analytical!Technologies!Inc.).!!Samples!were!run!in!duplicate!with!atropine!used!as!a!
standard!every!10!samples.!!Subsamples!of!dry!soil!from!all!sites!were!tested!for!carbonate!
minerals!and!concentrations!were!found!to!be!negligible.!!Aboveground!biomass!C!and!N!
stocks!were!calculated!by!multiplying!each!species’!tissue!%C!and!%N!by!its!total!dry!
biomass!and!then!summing!speciesJspecific!C!and!N!stocks!for!each!quadrat.!!Litter!and!soil!
C!and!N!stocks!were!calculated!by!multiplying!%C!or!%N!by!total!litter!mass.!!Soil!C!and!N!

30!

stocks!were!calculated!from!soil!%C!or!%N,!soil!bulk!density,!and!sampling!depth.!!Total!C!
and!N!ecosystem!stocks!were!calculated!by!summing!soil,!litter,!and!biomass!stocks!for!
each!site.!!Carbon!to!nitrogen!ratios!were!used!as!a!measure!of!organic!matter!(OM)!quality.!!
Low!C:N!ratios!indicate!high!quality!OM!and!high!C:N!ratios!indicate!recalcitrant!OM.!!
!

Plant!aboveground!tissue!%N!was!used!to!determine!plantJ!and!plotJlevel!nitrogen!

use!efficiencies!(NUE).!!NUE!was!defined!as!the!amount!of!biomass!produced!per!unit!N!
(van!Ruijuen!and!Berendse!2005)!and!was!calculated!on!the!plot!level!by!first!determining!
the!NUE!for!each!species!in!each!plot!(total!biomass!divided!by!the!tissue!N!content).!!
Though!similar,!NUE!is!not!perfectly!scaled!with!biomass!C:N!ratio!because!%C!varied!
among!species!(~!40!to!50!%C),!and,!therefore,!both!can!be!informative.!!This!is!an!
acceptable!way!to!calculate!NUE!in!this!study!because!all!species!were!collected!at!peak!
biomass!and!were!either!annual!or!perennial!deciduous!growth!forms,!in!which!all!biomass!
was!produced!during!a!single!growing!season.!!For!buttonbush!(woody!habit),!the!only!
abundant!species!with!perennial!aboveground!biomass,!leaves,!and!stems!were!separated!
and!an!NUE!estimate!was!made!using!leaf!tissue.!!A!weighted!NUE!average!was!then!
calculated!for!each!plot!and!averaged!for!each!site!(hereafter!called!the!Site!NUE).!
!
Estimation*of*plant*abundance*!
!

Percent!cover!was!estimated!for!every!plant!species!in!each!of!the!six!0.5!m2!

quadrats!at!each!site.!!This!percent!cover!was!then!assigned!to!a!cover!class!from!1!to!6!(1:!
0J5%!cover;!2:!6J25%;!3:!26J50%;!4:!51J75%;!5:!76J95%;!6:!96J100%).!!Shannon’s!
diversity!index!was!calculated!using!percent!cover!data!following!Seefeldt!and!McCoy!
(2003)!and!was!used!as!a!measure!of!biodiversity!(incorporating!both!species!richness!and!
31!

evenness).!!The!percent!of!the!total!biomass!from!invasive!species!(referred!to!hereafter!as!
invasive!species!dominance),!which!included!the!combined!biomass!of!Phragmites,!
Phalaris,!and!Typha,!was!calculated!by!dividing!their!combined!biomass!by!the!total!
biomass!in!each!quadrat.!!Native!species!dominance!was!calculated!similarly!(total!native!
species!biomass!divided!by!total!biomass)!with!nonJnative,!nonJinvasive!species!excluded!
from!both!metrics.!!Phalaris!%biomass!was!calculated!by!dividing!Phalaris!biomass!in!a!
quadrat!by!total!biomass!in!that!quadrat.!!In!some!cases!(see!statistical!analysis!section)!
Phalaris*was!analyzed!instead!of!the!invasive!species!category!due!to!its!presence!at!the!
majority!of!sites!sampled!(Table!2J1).!
!

!

Soil*carbon*quality*assay!
!

To!determine!dominant!species!effects!on!organic!matter!quality!(as!aerobic!C!

mineralization!rates)!in!these!wetlands,!a!laboratory!incubation!was!done!at!two!
temperatures!(7°C!and!23°C)!using!soils!collected!under!monospecific!stands!(>!90%!
cover)!of!the!three!most!dominant!species!sampled!during!the!survey!study.!!Monospecific!
stands!were!used!because!species!effects!on!soil!C!quality!are!more!likely!to!be!detected!
when!only!one!species!is!present.!!The!two!temperatures!used!represent!growing!season!
average!temperature!(~!23°C)!and!nonJgrowing!season!average!temperature!(~!7°C)!for!
southern!Michigan.!!Soils!were!incubated!at!two!temperatures!so!the!Q10!for!each!speciesJ
specific!soil!could!be!calculated.!!The!temperature!coefficient,!Q10,!is!a!metric!that!
describes!the!rate!of!change!in!a!biological!or!chemical!system!with!an!increase!of!10°C.!!
This!allowed!a!comparison!to!be!made!of!temperature!effects!on!C!mineralization!rates!due!

32!

to!dominant!species.!!Q10!was!calculated!with!the!following!equation:!!Q10!=!
(R2/R1)^10/(T2JT1),!where!R1!is!the!C!mineralization!rate!at!low!temperature,!R2!is!the!C!
mineralization!rate!at!high!temperature,!T1!is!the!low!temperature!and!T2!is!the!high!
temperature!in!degrees!Celsius!(Solondz!et!al.!2008).!!!
Eleven!wetland!sites!were!sampled!for!the!incubations:!4!Typha*dominated,!4!
Phalaris!dominated,!2!Phragmites!dominated!and!1!Carex*lacustris!dominated.!!For!a!site!to!
be!considered!dominated!by!a!specific!species,!that!species!had!to!consist!of!>!90%!of!the!
total!biomass.!!Because!the!aggressive!genotype!of!Phragmites!is!a!recent!invader!to!inland!
Michigan!(Hamilton,!personal!communication),!only!two!sites!from!the!24!that!were!
surveyed!could!be!classified!as!a!monospecific!stand.!!Additionally,!due!to!low!native!
species!abundance,!only!one!C.*lacustris!dominated!area!was!included!in!this!incubation.!!
Because!of!the!absence!of!replication!at!the!site!level,!C.*lacustris!was!left!out!of!statistical!
analyses!but!is!placed!in!some!figures!as!a!native!reference.!!Soil!samples!were!collected!in!
February!2007!at!the!end!of!the!growing!season.!!Five!soil!cores!(5!cm!depth)!were!
collected!at!each!site!using!a!linear!transect!similar!to!the!design!described!above!(11!sites!
x!5!cores!=!55!cores).!!These!soil!cores!were!sealed!in!whirlJpak!plastic!bags!(Nasco),!
immediately!placed!on!ice,!and!transported!to!the!laboratory!where!they!were!kept!frozen!
(J20°C)!until!the!start!of!the!incubation.*
!

Prior!to!the!start!of!the!incubation,!soils!were!thawed!at!room!temperature!for!24!

hours!and!hand!sieved!to!remove!rocks!and!large!roots.!!Each!soil!core!was!then!subJ
sampled!for!bulk!density!and!GWC!determination.!!The!dry!mass!of!the!subJsample!was!
measured!by!oven!drying!at!80°C!for!48!hours.!!Dry!mass!values!were!used!in!bulk!density!

33!

and!GWC!calculations.!!Dried!soils!were!then!ground!and!homogenized!using!a!mortal!and!
pestle!and!run!on!an!elemental!combustion!system!(Costech!ECS!4010,!Valencia,!CA)!for!
%C!and!%N!analysis.!!Samples!were!run!in!duplicate!with!atropine!used!as!a!standard!
every!10!samples.!!The!remaining!wet!soil!was!then!split!into!2!subsamples!of!
approximately!10!g!and!placed!into!a!250!mL!incubation!jar!(Chromatographic!Specialties,!
Inc.;!Ontario,!Canada).!!These!incubation!samples!were!equilibrated!for!7!days!at!4°C!to!
allow!the!C!mineralization!pulse!from!root!death!to!pass!(Weintraub!and!Schimel!2003).!!
Duplicate!jars!were!then!randomly!assigned!a!temperature!treatment,!flushed!with!
ambient!air!(~!400!ppmv!CO2),!and!loosely!sealed!with!lids!fitted!with!septa!to!allow!room!
air!to!enter!the!jar!until!the!start!of!a!CO2!extraction!round!(see!below).!!The!two!
temperature!treatments!consisted!of!high!temperature!(room!temperature,!~!23°C)!and!
low!temperature!(cold!room,!~!7°C).!!All!jars!(110!total;!4!vegetation!classes!x!1,!2,!or!4!
replicate!sites!x!5!replicate!cores!per!site!x!2!temperatures)!were!incubated!in!the!dark!for!
36!days.!!Similar!soil!moisture!conditions!were!created!across!all!incubation!samples!by!
bringing!each!to!a!comparable!moisture!content!using!distilled!water!before!the!beginning!
of!the!experiment!(40J60%!representing!ideal!nonJlimiting!conditions).!!Moisture!content!
was!maintained!weekly!over!the!course!of!the!incubation!by!adding!an!appropriate!volume!
of!distilled!water!after!each!jar!was!weighed!to!determine!water!loss.*
!

Carbon!mineralization!rates!were!estimated!for!six!24Jhour!periods!over!the!36Jday!

experiment,!on!days!1,!3,!8,!15,!22,!and!36.!!During!each!period,!a!10!mL!headspace!gas!
sample!was!taken!from!each!jar!immediately!after!jars!were!sealed!(time!=!0)!using!a!threeJ
way!stopcockJfitted!syringe,!and!then!every!12!hours!over!the!24!hour!period,!except!for!

34!

the!first!round,!which!was!48!hours.!!Before!gas!samples!were!extracted,!each!jar!was!
shaken!by!hand!to!mix!soil!pore!spaces!and!to!release!trapped!gas!bubbles.!!After!
headspace!samples!were!collected,!jars!were!injected!with!10!mL!of!N2!gas!to!ensure!
constant!air!pressure!and!volume.!!After!each!round,!lids!were!removed,!samples!were!
gently!flushed!with!ambient!air,!and!jars!were!wrapped!with!plastic!wrap!to!prevent!
moisture!loss.!!!
!

Each!10!mL!headspace!sample!was!analyzed!for!CO2!partial!pressure!by!injecting!5!

mL!of!sample!into!a!PPJsystem!EGMJ4!infrared!gas!analyzer!(IRGA).!The!IRGA!was!
standardized!using!a!CO2!standard!gas!after!every!10!injections.!!Carbon!dioxide!
concentrations!were!corrected!for!headspace!dilution!caused!by!the!added!N2!gas.!!The!
slope!of!CO2!concentrations!over!the!incubation!period!was!used!to!calculate!overall!C!
mineralization!rates.!!These!overall!mineralization!rates!were!divided!by!soil!dry!weight!
(g)!to!report!data!on!a!mass!basis!(umol!CO2!gJ1!dayJ1)!and!by!total!soil!C!(SC)!to!report!
data!on!a!SC!basis!(umol!CO2!gJ1!SC!dayJ1).!!Slopes!were!discarded!if!R2!values!were!less!
than!0.75,!which!comprised!less!than!2%!of!the!slopes.!!
!
N*mineralization*and*nitrification*assay*
To!determine!rates!of!net!N!mineralization!and!nitrification!in!these!wetlands,!an!
aerobic!laboratory!incubation!was!conducted!using!soils!collected!under!monospecific!
stands!(>!90%!cover)!of!Phragmites,!Phalaris,!and!Typha.!!Eight!wetland!sites!were!used!in!
all:!3!Typha*dominated,!3!Phalaris!dominated,!and!2!Phragmites!dominated,!and!were!a!

35!

subset!of!the!wetlands!used!for!the!C!quality!incubation.!!Soil!samples!were!collected!at!the!
end!of!the!2008!growing!season.!!Three!soil!cores!(10!cm!depth)!were!collected!at!each!site!
from!permanent!plots!that!were!established!during!the!summer!of!2008!as!part!of!a!larger!
research!project!(8!sites!x!3!cores!=!24!cores).!!These!soil!cores!were!sealed!in!whirlJpaks!
(Nasco,!Fort!Atkinson,!WI),!immediately!placed!on!ice,!and!transported!to!the!laboratory!
where!they!were!kept!at!4°C!for!2!days!until!the!start!of!the!incubation!to!reduce!microbial!
activity.*
Soil!samples!for!assays!of!N!mineralization!and!nitrification!were!processed!
similarly!to!the!C!mineralization!soil!samples.!!After!sieving,!10!g!subJsamples!were!taken!
from!the!remaining!wet!soil:!one!subJsample!was!used!to!determine!initial!NO3J!and!NH4+!
concentrations!by!the!KCl!extraction!method!(Robertson!1999),!while!the!other!was!placed!
in!a!100!ml!plastic!container.!!After!30!days!of!aerobic!incubation!at!room!temperature,!the!
KCl!extraction!method!was!used!to!determine!final!NO3J!and!NH4+!concentrations.!!All!
extracts!were!analyzed!by!the!microplate!method!for!nitrate!and!ammonium!using!
protocols!developed!by!Dr.!David!Rothstein!(Dept.!of!Forestry,!MSU).!!Net!rates!of!N!
mineralization!and!nitrification!were!calculated!from!the!changes!in!inorganic!N!(NH4+!+!
NO3J)!or!NO3J,!respectively,!during!the!incubation!period!(initial!–!final!pool!sizes).!!Similar!
soil!moisture!conditions!were!created!across!all!incubation!samples!by!the!same!method!
used!in!the!C!quality!incubation.!!N!mineralization!and!nitrification!rates!were!calculated!on!
a!soil!mass!and!soil!carbon!basis!similar!to!the!C!quality!incubation.!
!
*
36!

Statistical*analyses*
Wetland!survey(
Because!the!majority!of!wetlands!sampled!were!invaded!by!Phalaris,!Phragmites,!
and/or!Typha!(23!out!of!24;!Table!2J1)!simple!linear!regression!(SLR)!analysis!was!used!to!
determine!the!relationship!between!site!Shannon!diversity!index!and!invasive!species!
dominance!(%biomass!of!total!community!biomass)!(Hypothesis!1).!!To!address!hypothesis!
2,!another!SLR!was!performed!to!determine!the!relationship!between!vegetation!NUE!and!
invasive!species!dominance.!!For!Shannon!diversity!and!NUE!SLRs,!all!24!wetlands!were!
included;!for!the!other!analyses!only!20!wetlands!were!used!due!to!incomplete!datasets!
from!4!wetlands.!!!
To!address!hypothesis!3,!general!linear!models!were!constructed!to!determine!the!
controlling!factors!for!biomass,!litter,!soil,!and!total!ecosystem!C!and!N!stocks.!!To!explore!
species!controls!on!biomass!C!and!N!stocks,!I!constructed!general!linear!models!using!
species!composition!data!(invasive!species!and!native!species!dominance!or!biomass)!as!
predictor!variables.!!Invasive!and!native!species!dominance!(percent!of!plant!community)!
was!used!instead!of!invasive!and!native!biomass!for!biomass!C!stocks!because!there!is!an!
allometric!relationship!between!biomass!C!and!total!biomass,!therefore!these!variables!
would!be!autoJcorrelated.!!This!allometric!relationship!does!not!necessarily!exist!for!
biomass!N!stock!because!species’!NUE!can!influence!the!amount!of!biomass!%N!present.!!
For!this!reason!invasive!species!biomass!was!used!to!predict!biomass!N!stocks.!!For!litter!C!
and!N!stocks,!species!composition!data!and!aboveground!biomass!chemistry!(%C,!%N,!and!
C:N!ratio)!were!used!as!predictor!variables.!!After!no!significance!was!found!for!any!plant!
community!predictor!variable,!Phalaris!abundance!was!included!as!a!predictor!variable!in!

37!

place!of!invasive!species!dominance!due!to!its!presence!at!most!sites!(Table!2J1).!!To!
determine!species!effects!on!soil!C!and!N!stocks!and!soil!C:N!ratios,!general!linear!models!
were!constructed!that!included!plant!community!composition,!litter!chemistry!(%N,!%C,!
and!C:N!ratio),!and!litter!quantity!(mass!and!bulk!density)!as!predictor!variables.!!Finally,!
for!total!ecosystem!C!and!N!stocks,!general!linear!models!were!constructed!using!plant!
community!data!as!predictor!variables.!!No!lower!level!categories!(soil,!litter,!or!biomass!
characteristics)!could!be!included!as!predictors!because!those!data!were!used!to!calculate!
related!stocks,!and!thus!would!be!autoJcorrelated!with!total!ecosystem!stocks.!!!
For!all!general!linear!models,!site!ID!was!included!in!the!model!as!a!random!factor,!
treating!the!design!as!nested!(quadrats!nested!within!site).!!Model!selection!procedures!
based!on!Akaike’s!information!criterion!(AIC)!values!were!used!following!Zuur!et!al.!
(2009).!!Briefly,!the!most!complex!biologically!meaningful!model!(i.e.,!the!most!complex!
model!constructed!from!nonJautocorrelated!terms!that!hypothetically!could!influence!the!
predictor!variable)!was!compared!to!models!of!decreasing!complexity!based!on!individual!
model!AIC!values.!!The!bestJfit!model!was!the!one!with!the!lowest!AIC!value!and!highest!
Akaike!weights!(wi),!which!describe!the!weight!of!evidence!for!one!model!compared!to!the!
other!models.!!Once!the!best!model!was!selected!a!tTable!(R!code)!data!frame!was!
constructed!to!determine!individual!variable!significance.!!Here!I!mainly!report!results!for!
the!final!“bestJfit”!model.!!!Full!model!selection!results!can!be!found!in!Appendix!A.!!
Wetland!classification!(see!above)!was!also!included!as!a!predictor!variable!to!the!bestJfit!
model!determine!if!its!inclusion!would!improve!the!fit!of!the!model,!therefore!minimizing!
the!possible!confounding!effect!of!wetland!class!on!C!and!N!stocks!(for!instance,!if!
depressional!wetlands!have!high!OM!accumulation!independent!of!plant!community,!but!
38!

also!were!highly!invaded).!!In!all!cases!adding!wetland!classification!improved!the!fit!of!the!
model!(i.e.,!it!lowered!the!model!AIC),!but!in!no!case!was!wetland!classification!significant!
and!is!therefore!left!out!of!the!results!section.!!Model!diagnostics!were!assessed!for!the!
bestJfit!model!to!determine!if!the!residuals!were!normally!distributed!and!displayed!
constant!error!variances.!!Log!transformations!were!used!to!correct!for!any!
heteroscedasticity.!!All!statistical!tests!were!performed!in!R!(version!2.11.1,!2010).!!!
!
Assays!of!C!quality!and!N!transformations!
The!general!goals!for!the!statistical!analysis!of!the!C!quality!assays!were!twofold:!(1)!
to!determine!treatment!(vegetation!type!and!temperature)!effects!on!C!mineralization!
rates!and!(2)!to!explore!the!relationships!between!C!mineralization!and!organic!matter!
quality!(C:N!ratio)!(hypothesis!4).!!To!investigate!treatment!effects!on!C!mineralization!
rates,!I!used!a!repeated!measures!analysis!of!variance!(ANOVA)!and!Tukey’s!HSD!multiple!
comparison!tests!were!used!to!determine!vegetation!and!temperature!effects,!as!well!as!
their!interaction!on!C!mineralization!rates.!!For!the!ANOVA,!soil!core!ID!was!nested!within!
site!and!included!as!a!random!effect.!!I!used!linear!regression!models!to!examine!the!effects!
of!soil!C:N!ratios!on!C!mineralization!rates.!!Species!effects!on!Q10!values,!litter!and!soil!%C,!
%N,!and!C:N!ratios!and!N!transformation!rates!were!determined!using!general!linear!
models.!!All!statistical!tests!were!performed!in!R!(version!2.11.1,!2010).!!!!
!
(
(
(

39!

(
Table!2J1.!!GPS!coordinates!of!the!24!survey!sites!with!their!hydrological!classification,!
which!is!based!on!magnesium!concentrations!(see!methods!for!more!details),!and!the!
presence!or!absence!of!the!most!dominant!invasive!species.!Phalaris!=!Phalaris*
arundinacea,!Typha!=!Typha!xglauca,!Phragmites!=!Phragmites*australis.!

(

Site!
LLP!
LS!
LTER!
NLCL!
NLCLP!
P1!
P11!
P18!
P26N!
P26S!
P3!
P5!
P8!
P9!
Parker!
SMCL!
SP7!
SWMCL!
SWP7!
TM!
TM2!
WMCL!
EF1!
LOP!

Classification!
precipitation!
precipitation!
precipitation!
lake!
lake!
precipitation!
precipitation!
intermediate!
intermediate!
intermediate!
precipitation!
intermediate!
intermediate!
precipitation!
lake!
lake!
intermediate!
lake!
intermediate!
groundwater!
groundwater!
lake!
lake!
groundwater!

Phalaris*
!
X!
X!
X!
!
X!
X!
X!
X!
X!
X!
X!
X!
X!
X!
!
X!
!
X!
X!
X!
!
!
!

Typha*
!
!
!
X!
X!
!
!
X!
X!
X!
!
!
!
!
!
X!
X!
!
X!
!
X!
X!
X!
!

Phragmites* GPS!Coordinates!
X!
42°!46.117N,!085°!23.533W!
!
42°!24.228N,!085°!23.087W!
!
42°!24.794N,!085°!22.455W!
!
42°!28.287N,!085°!27.128W!
X!
42°!28.254N,!085°!27.782W!
!
42°!29.352N,!085°!27.100W!
!
42°!28.339N,!085°!27.696W!
!
42°!28.733N,!085°!27.553W!
!
42°!28.689N,!085°!27.768W!
!
42°!28.689N,!085°!27.768W!
!
42°!29.341N,!085°!28.424W!
!
42°!28.518N,!085°!27.882W!
!
42°!28.274N,!085°!27.797W!
!
42°!28.267N,!085°!27.726W!
!
42°!28.926N,!085°!27.753W!
X!
42°!28.737N,!085°!27.547W!
!
42°!28.396N,!085°!27.862W!
X!
42°!28.965N,!085°!27.861W!
!
42°!28.285N,!085°!28.005W!
!
42°!24.497N,!085°!24.455W!
!
42°!24.497N,!085°!24.455W!
!
42°!28.965N,!085°!27.861W!
!
42°!21.414N,!085°!21.939W!
!
42°!22.101N,!085°!21.656W!

(
(
(
(
(
(

40!

Results(
Wetland*survey!
TwentyJthree!of!the!24!wetlands!surveyed!were!invaded!by!at!least!one!of!the!three!
focal!invasive!species!(Phragmites,!Phalaris,!and!Typha).!!As!invasive!species!dominance!
increased,!Shannon!Diversity!decreased!(Figure!2J1;!adjusted!R2!=!0.75,!p!<!0.001).!!A!
marginally!significant!positive!relationship!was!found!between!site!nutrient!use!efficiency!
(NUE)!and!invasive!species!biomass!(Figure!2J2;!adjusted!R2!=!0.10,!p!=!0.08),!though!this!
relationship!was!mainly!due!to!one!site,!which!was!a!monospecific!stand!of!Phragmites!that!
produced!a!lot!of!biomass!and!had!a!high!NUE.!!After!excluding!this!site,!there!was!no!
relationship!between!NUE!and!invasive!species!biomass.!!Additionally,!there!was!a!
significant!positive!relationship!between!total!biomass!and!invasive!species!biomass!
(Figure!2J3;!adjusted!R2!=!0.61,!p!<!0.001).!
!

The!model!that!included!both!invasive!species!and!native!species!dominance!was!

the!best!for!predicting!biomass!C!stock!(Table!2J2).!!This!model!had!an!Akaike!weight!(wi!)!
of!1.00,!giving!strong!support!for!this!model,!while!there!was!little!support!for!the!null!
model!(intercept!only)!(wi!!<!0.001).!!Both!invasive!and!native!species!biomass!had!a!
positive!effect!on!biomass!C!stocks,!though!neither!was!significant.!!For!biomass!N!stock,!
the!model!containing!only!total!biomass!was!the!best!fit!(wi!!=!0.99).!!In!this!model,!total!
biomass!had!a!significant!positive!relationship!with!biomass!N!stock!(Table!2J2),!and!
similar!to!biomass!C!stock,!the!null!model!had!very!little!explanatory!power!(wi!!<!0.001).!

41!

The!most!parsimonious!model!for!litter!C!stock!contained!biomass!%C,!%N,!and!C:N!
ratio!as!predictor!variables!(Table!2J3;!wi!=!0.48).!The!model!containing!Phalaris*
arundinacea!biomass!and!biomass!%C,!%N,!and!C:N!ratio!had!an!Akaike!weight!of!0.29!and!
a!∆AIC!value!of!less!than!2,!giving!support!for!both!models,!though!there!is!more!support!
for!the!model!that!excluded!P.*arundinacea!biomass!(based!on!a!higher!Akaike!weight).!!In!
the!bestJfit!model,!biomass!%N!and!C:N!ratio!had!a!positive!effect!on!litter!C!stock,!while!
biomass!%C!had!a!negative!effect,!though!no!variable!in!the!bestJfit!model!was!significant!
(Table!2J3).!!There!was!little!support!for!any!of!the!candidate!models!having!a!greater!fit!
than!the!null!model!for!litter!N!stock.!!The!bestJfit!model!contained!biomass!%N!(Table!2J3;!
wi!=!0.61)!but!was!less!than!2!∆AIC!from!the!null!model,!giving!little!evidence!for!this!model!
fitting!the!data!in!a!meaningful!way.!!In!the!bestJfit!model,!biomass!%N!had!a!positive!effect!
on!litter!N!stocks.!!The!most!parsimonious!model!for!predicting!litter!C:N!ratios!contained!
invasive!species!biomass!and!biomass!%N!(Table!2J3;!wi!=!0.45).!!In!the!bestJfit!model,!
biomass!%N!had!a!significant!negative!relationship!with!litter!C:N!ratios!(Figure!2J4),!
meaning!that!as!biomass!%N!increased,!litter!C:N!ratio!decreased,!showing!the!tight!link!
between!standing!biomass!nutrient!concentrations!and!litter!quality.!!Invasive!species!
biomass!had!a!positive!relationship!with!litter!C:N!ratio,!though!this!relationship!was!not!
significant.!
!

For!soil!C!stock,!the!full!model,!which!included!invasive!biomass,!native!biomass,!

litter!mass,!litter!%C!and!%!N,!and!C:N!ratio!(Table!2J4;!wi!=!0.68),!was!more!than!three!
times!more!plausible!than!the!next!best!approximating!model.!!In!the!full!model,!invasive!
species!biomass!had!a!significant!positive!relationship!and!with!soil!C!stocks!(Figure!2J5).!!
42!

Also,!litter!mass!had!a!marginally!significant!negative!relationship!with!soil!C!stock.!!In!the!
bestJfit!model,!native!species!biomass,!litter!%C,!%N,!and!C:N!ratio!all!had!a!positive!effect!
on!soil!C!stocks,!though!they!were!not!statistically!significant.!!The!candidate!model!
containing!native!species!biomass,!litter!mass,!litter!%C!and!%N,!and!C:N!ratio!was!the!best!
fit!model!for!predicting!soil!N!stocks!(Table!2J4;!wi!=!0.72).!!In!this!model,!native!species!
biomass!and!litter!mass!both!had!a!significant!negative!effect!on!soil!N!stocks,!with!litter!
mass!having!a!slightly!larger!effect.!!Though!not!significant,!litter!%C!and!C:N!ratio!had!a!
negative!effect!on!soil!N!stocks,!while!litter!%N!had!a!positive!effect!on!soil!N!stock.!!For!
soil!quality!(C:N!ratio),!the!model!that!contained!litter!%N!as!the!only!predictor!variable!
was!the!bestJfit!model!(Table!2J4;!wi!=!0.76).!!In!the!bestJfit!model,!litter!%N!had!a!
significant!positive!influence!on!soil!C:N!ratios,!meaning!as!the!litter!N!content!increased!so!
did!soil!C:N!ratios.!
!

Of!the!four!candidate!models!predicting!ecosystem!C!stock,!the!most!parsimonious!

contained!both!invasive!species!and!native!species!biomass!(Table!2J5;!wi!=!0.74).!!For!this!
model,!invasive!species!biomass!had!a!significant!positive!relationship!with!ecosystem!C!
stock!(Figure!2J6).!!For!ecosystem!N!stock,!the!candidate!model!containing!only!native!
species!biomass!was!the!most!approximating!(Table!2J5;!wi!=!0.51),!though!the!null!model!
had!a!∆AIC!less!than!2!giving!support!to!both!models.!!For!the!bestJfit!model,!native!species!
biomass!had!a!significant!negative!relationship!with!ecosystem!N!stock,!meaning!that!as!
native!species!biomass!increased,!ecosystem!N!stocks!decreased,!which!is!similar!to!the!
relationship!native!species!biomass!had!on!soil!N!stocks.!!!
!
43!

Soil*carbon*quality*assay!
Carbon!mineralization!(CJmin)!rates!were!fairly!constant!over!the!duration!of!the!
36Jday!incubation!for!most!treatment!combinations,!except!for!the!Phalaris!soil!at!high!
temperature,!which!decreased!over!the!first!15!days!but!then!stabilized!throughout!the!end!
of!the!incubation!(Figure!2J7;!significant!threeJway!interaction,!p!=!0.001;!Table!2J6).!!
Phalaris!soil!at!high!temperature!also!had!the!greatest!CJmin!rates!over!the!duration!of!the!
experiment.!!At!high!temperature,!Typha!soil!CJmin!rates!were!significantly!less!than!
Phalaris,!but!greater!than!Phragmites,!suggesting!that!Phalaris!soil!was!the!most!labile!and!
Phragmites!was!the!most!recalcitrant.!!Carbon!mineralization!rate!of!Phragmites!soil!at!high!
temperature!was!not!statistically!different!from!Phalaris!soil!at!low!temperature.!!The!same!
rank!order!of!soil!lability!was!found!at!low!temperature!and!high!temperature:!Phalaris!>!
Typha!>!Phragmites!(significant!species!main!effect,!p!=!0.03;!Table!2J6).!!As!expected,!
carbon!mineralization!at!high!temperature!was!greater!than!low!temperature!among!all!
species!(significant!temperature!main!effect,!p!<!0.001;!Table!2J6).!!
Cumulative!CJmin!showed!a!pattern!similar!to!CJmin!rates:!Phalaris!soil!had!the!
greatest!cumulative!CJmin,!followed!next!by!Typha!soil,!and!then!finally!Phragmites!soil,!
and!this!pattern!was!the!same!at!both!temperatures,!though!high!temperatures!led!to!
higher!cumulative!CJmin!than!low!temperatures!(Figure!2J8;!significant!main!effects!of!
species!and!temperature,!p!=!0.03!and!p!<!0.001,!respectively;!Table!2J7).!!Similar!to!CJmin!
rates,!cumulative!CJmin!results!suggest!that!Phalaris!soil!is!more!labile!than!either!Typha!or!
Phragmites!soil,!with!the!latter!being!the!least!labile.!
There!were!significant!species!effects!on!preJincubation!soil!%C,!%N,!and!C:N!ratio!
(Table!2J8).!!Typha!and!Phragmites!soil!had!highest!soil!%C,!while!Phalaris!had!the!lowest!

44!

(significant!species!effect,!p!<!0.05).!!Soil!%N!followed!a!similar!pattern!with!Typha!and!
Phragmites!having!the!greatest!soil!%N!and!Phalaris!the!least!(significant!species!effect,!p!=!
0.05).!!Although!not!significant,!Typha!did!have!a!greater!amount!of!soil!%N!than!
Phragmites,!which!is!reflected!in!their!difference!in!soil!C:N!ratio.!!Soil!C:N!ratio!was!the!
highest!in!Phragmites!soil!and!lowest!in!Typha!and!Phalaris!soil!(significant!species!effect,!p!
=!0.01).!!Phalaris*arundinacea!soil!C:N!ratio!showed!the!most!variation!and!was!not!
statistically!different!from!Typha!soil.!!!
To!determine!if!litter!chemistry!followed!a!similar!pattern!as!soil!chemistry,!litter!
%C,!%N,!and!C:N!ratios!were!analyzed!for!species!effects!(Table!2J8).!!There!was!no!
difference!in!litter!%C!among!species,!but!Phalaris!had!the!highest!litter!%N!compared!to!
Typha!and!Phragmites!litter!(marginally!significant!species!effect,!p!=!0.08).!!Litter!C:N!ratio!
followed!a!similar!pattern!as!soil!C:N!ratio:!Phragmites!litter!had!the!highest!litter!C:N!ratio!
and!Phalaris!had!the!lowest!litter!C:N!ratio!(significant!species!effect,!p!=!0.03).!
To!determine!possible!controls!on!cumulative!CJmin,!linear!and!nonlinear!
regression!was!used!to!verify!the!predicted!influence!soil!C:N!ratio!(quality)!has!on!
decomposition!rates.!!As!predicted,!there!was!a!negative!relationship!between!cumulative!
CJmin!at!high!(Figure!2J9;!adjusted!R2!=!0.53,!p!<!0.001)!and!low!(Figure!2J9;!adjusted!R2!=!
0.40,!p!<!0.001)!temperatures!and!soil!C:N!ratio.!!Soil!C:N!ratio!was!a!better!predictor!of!
cumulative!CJmin!than!soil!%C!(high!temperature:!adjusted!R2!=!0.28;!low!temperature:!
adjusted!R2!=!0.24)!or!%N!(high!temperature:!adjusted!R2!=!0.17;!low!temperature:!
adjusted!R2!=!0.12).!

45!

As!discussed!in!the!methods!section,!Q10!is!a!metric!that!describes!the!rate!of!
change!in!a!biological!or!chemical!system!with!an!increase!of!10°C,!and!using!Q10!allows!a!
comparison!to!be!made!of!temperature!effects!on!CJmin!rates!due!to!species.!!Though!there!
was!a!pattern!to!the!effect!species!had!on!Q10,!with!Typha!soil!having!the!lowest!Q10!and!
Phragmites!and!Phalaris!soil!having!almost!equal!Q10,!this!was!only!marginally!significant!
(Figure!2J10;!F2,8!=!3.46,!p!=!0.083).!!These!results!suggest!that!Typha!soil!is!more!resistant!
to!the!effects!of!temperature!change!than!the!other!species’!soil.!
!
N*mineralization*and*nitrification*assay!
!

Potential!N!mineralization!and!nitrification!rates!were!almost!identical!because!the!

majority!of!the!ammonium!mineralized!was!nitrified!to!nitrate.!!Nitrogen!mineralization!
rates!were!greatest!in!Phalaris!soil!and!the!least!in!Typha!soil!(Figure!2J11;!significant!
species!effect,!F2,5!=!20.93,!p!=!0.003).!!Nitrification!followed!a!similar!pattern,!though!
slightly!less!so!(marginally!significant!species!effect,!p!=!0.06).!!The!low!N!mineralization!
and!nitrification!rates!of!Phragmites!soil!is!in!agreement!with!the!CJmin!results!that!
suggested!Phragmites*soil!is!more!recalcitrant!than!soil!collected!from!other!invasive!
species!monospecific!stands.!!Though!there!were!no!significant!differences!in!soil!C:N!ratios!
among!the!three!soils!collected!for!this!incubation!(p!=!0.46),!there!were!significant!
differences!among!species!for!soil!%C!and!%N!(significant!species!effect,!both!p!<!0.01;!
Table!2J9).!!These!differences!were!mainly!caused!by!Phragmites!soil!having!greater!%C!
and!%N,!though!Typha!soil!did!have!slightly!greater!%C!than!Phalaris!soil.!!Soil!C:N!ratio!

46!

did!not!have!a!significant!relationship!with!N!mineralization!rates!(adjusted!R2!=!0.04,!p!=!
0.17).!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
47!

!
Table!2J2.!Summary!of!the!bestJfit!model!for!biomass!C!and!N!stocks.!!Dominance!
refers!to!the!proportion!of!the!total!biomass!from!invasive!or!native!species.!!Terms!
in!bold!indicate!significant!predictors.!!Df!(Den)!indicates!the!denominator!degrees!of!
freedom.!
Biomass*C*Stock*
Term!
Invasive!Species!Dominance!
Native!Species!Dominance!
!
Biomass*N*Stock*

!

Term!
Total(Biomass(

estimate!
475.18!
444.39!

!

estimate!
0.02!

tJvalue!
0.49!
0.45!

!

tJvalue!
11.65!

Df!(Den)!
97!
97!

!

Df!(Den)!
98!

PJvalue!
0.627!
0.650!

PJvalue!
<!0.001!

!
!
!
Table!2J3.!Summary!of!the!bestJfit!model!for!litter!C!and!N!stocks!and!litter!C:N!ratios.!!
Terms!in!bold!indicate!significant!predictors.!!Df!(Den)!indicates!the!denominator!
degrees!of!freedom.!
Litter*C*Stock*
Term!
Biomass!%N!
Biomass!%C!
Biomass!C:N!
!
Litter*N*Stock*
Term!
Biomass!%N!
!
Litter*Quality*(C:N*Ratio)*
Term!
Invasive!Species!Biomass!
Biomass(%N(

!

!

estimate!
72.29!
J2.50!
0.57!

estimate!
0.92!

estimate!
4.70!
J15.97!

!
!
!
!
!
!
!

48!

!

!

tJvalue!
0.55!
J0.48!
0.18!

tJvalue!
0.43!

tJvalue!
1.06!
J3.6!

!

!

Df!(Den)!
96!
96!
96!

Df!(Den)!
98!

Df!(Den)!
97!
97!

!

!

PJvalue!
0.585!
0.631!
0.868!

PJvalue!
0.667!

PJvalue!
0.292!
<!0.001!

Table!2J4.!Summary!of!the!bestJfit!model!for!soil!C!and!N!stocks!and!soil!C:N!ratios.!!
Terms!in!bold!indicate!significant!predictors.!!Df!(Den)!indicates!the!denominator!
degrees!of!freedom.!
Soil*C*Stock*
Term!
Invasive(Species(Biomass(
Native!Species!Biomass!
Litter(Mass(
Litter!%C!
Litter!%N!
Litter!C:N!
!
Soil*N*Stock*
Term!
Native(Species(Biomass(
Litter(Mass(
Litter!%C!
Litter!%N!
Litter!C:N!
!
Soil*Quality*(C:N*Ratio)*

!

estimate!
2.43!
2.04!
J0.97!
39.55!
1363.80!
14.63!

!

estimate!
J0.48!
J0.13!
J4.37!
21.80!
J0.83!
!

Term!
Litter(N(

tJvalue!
2.02!
0.81!
J1.98!
0.96!
1.49!
0.54!

!

tJvalue!
J2.29!
J2.87!
J1.16!
0.27!
J0.34!
!

estimate!
1.21!

Df!(Den)!
93!
93!
93!
93!
93!
93!

!

Df!(Den)!
92!
92!
92!
92!
92!
!

tJvalue!
2.27!

PJvalue!
0.046!
0.423!
0.051!
0.338!
0.138!
0.590!

PJvalue!
0.024!
0.005!
0.250!
0.791!
0.734!
!

Df!(Den)!
98!

PJvalue!
0.025!

!
!
!
Table!2J5.!Summary!of!the!bestJfit!model!for!ecosytem!C!and!N!stocks.!!Terms!in!bold!
indicate!significant!predictors.!!Df!(Den)!indicates!the!denominator!degrees!of!
freedom.!
Ecosystem*C*Stock*
Term!
Invasive(Species(Biomass(
Native!Species!Biomass!
!
Ecosystem*N*Stock*
Term!
Native(Species(Biomass(

estimate!
2.91!
2.74!
!

tJvalue!
2.34!
1.04!
!

estimate!
J0.43!

!
!
!

49!

Df!(Den)!
97!
97!
!

tJvalue!
J2.05!

PJvalue!
0.021!
0.297!
!

Df!(Den)!
98!

PJvalue!
0.043!

!
Table!2J6.!Results!of!repeated!measures!ANOVA!for!the!effect!of!Species,!
Temperature!and!Time!on!C!mineralization!throughout!the!36!day!incubation.!!
!
Between*Subjects*
*
Source!
!
Species!
!
Temperature!
!
Species!x!
Temperature!
!
Within*Subjects*
*
Source!
!
Time!
!
Time!x!Species!
!
Time!x!Temperature!
!
Time!x!Species!x!
Temp.!
**
!
!
!

!
!
!

!
!
!

!
!
!

!
!
!

!num!df!
!
2!
!
1!
!

den!df!
!
8!
!
47!
!

F!
!
5.29!
!
423.02!
!

PJvalue!
!
0.0340!
!
<0.0001!
!

2!
!
!
!
!num!df!
!
1!
!
2!
!
1!
!

47!
!
!
!
den!df!
!
494!
!
494!
!
494!
!

8.32!
!
!
!
F!
!
1.26!
!
4.89!
!
3.16!
!

0.0008!
!
!
!
PJvalue!
!
0.2620!
!
0.0079!
!
0.0763!
!

2!

494!

7.00!

0.0010!

!!

!!

!!

!!

Table!2J7.!Summary!of!ANOVA!examining!the!effect!of!Species!and!
Temperature!on!cumulative!C!mineralization.!!
!
!
Source!
Species!
Temperature!
S!x!T!

!
df!
2!
1!
2!

!
den!df!
8!
47!
47!

!
F!
5.82!
1673.30!
2.05!

!
!
!
!
!
50!

P>F!
0.0276!
<!0.0001!
0.1398!

!
!
!
!
!
!

!
!
!
!
!
!

Table!2J8.!Soil!and!litter!%C,!%N,!and!C:N!ratio!of!the!four!species!used!in!the!
organic!matter!quality!incubation.!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!Values!are!means!
±!SE.!
Litter!
Litter!
Litter!
Species!
Soil!%C!
Soil!%N!
Soil!C:N!
%C!
%N!
C:N!
18.5!
1.29!
14.3!
42.7!
1.07!
42.0!
Phragmites*
±4.2a!
±0.31a!
±0.5a!
±1.5!
±0.20a!
±6.9a!
10.7!
0.87!
12.0!
40.4!
1.68!
25.5!
Phalaris*
±3.1b!
±0.21b!
±0.8b!
±1.8!
±0.20b!
±3.4b!
18.2!
1.56!
11.7!
40.6!
1.23!
34.3!
Typha*
±2.4a!
±0.22a!
±0.3b!
±3.5!
±0.15a!
±6.6c!
10.5!
0.88!
12.1!
Carex*
no*data* no*data* no*data*
±3.2b!
±0.28b!
±0.6b!

Table!2J9!Soil!%C,!%N,!and!C:N!ratio!of!the!four!species!
used!in!the!N!mineralization/nitrification!incubation.!!
Same!letter!superscript!denotes!nonsignificant!
differences!according!to!Tukey!post!hoc!tests.!Values!are!
means!±!SE.!
Species!
Soil!%C!
Soil!%N!
Soil!C:N!
a!
a!
Phragmites* 31.7!±4.9
2.27!±0.35
14.0!±0.4!
b!
b!
Phalaris*
4.3!±0.8
0.30!±0.06
14.7!±0.7!
Typha*
8.5!±2.3c!
0.59!±0.16b!
14.7!±0.7!

!
!
!
!
!
!
!
!
!
!

!

51!

!
!
!
!
!
!
!
!
1.4"

Shannon&Diversity&

1.2"
1"
0.8"
0.6"
0.4"
0.2"
0"
0"

0.2"

0.4"

0.6"

0.8"

1"

Invasive&Species&Dominance&

Figure!2J1.!!Regression!between!invasive!species!dominance!(percent!biomass!of!
community)!and!Shannon!Diversity!index!(adjusted!R2!=!0.75,!p!<!0.001).!
!
!
!
!
!
!
!
!
!
!
!
!
!
!

52!

!

!
!
!
!
!
!
!
!
160"
140"

Site%NUE%

120"
100"
80"
60"
40"
20"
0"
0"

100"

200"

300"

400"

500"

600"

700"

800"

Invasive%Species%Biomass%(g%m52)%

!
Figure!2J2.!!Regression!between!invasive!species!biomass!(cumulative!biomass!of!
Phragmites!australis,!Phalaris*arundinacea,!and*Typha!spp.)!and!site!nitrogen!use!efficiency!
(adjusted!R2!=!0.10,!p!=!0.08).!
!
!
!
!
!
!
!
!
!
!
!
!

53!

!
!
!
!
!
!
!
!
!
!
900"

Total&Biomass&(g&m-2)&

800"
700"
600"
500"
400"
300"
200"
100"
0"
0"

100"

200"

300"

400"

500"

600"

700"

800"

900"

Invasive&Species&Biomass&(g&m-2)&

!
Figure!2J3.!Regression!between!invasive!species!biomass!(cumulative!biomass!of!
Phragmites!australis,!Phalaris*arundinacea,!and*Typha!spp.)!and!total!biomass!(adjusted!R2!
=!0.61,!p!<!0.001).!
!
!
!
!
!
!
!
!
!
!
!
!
!
54!

!
!
!
!
!
!
!
!
!
!
60"

Li#er&C:N&Ra,o&

50"
40"
30"
20"
10"
0"
0.6"

0.8"

1"

1.2"
Biomass&%&N&

1.4"

1.6"

!

Figure!2J4.!Regression!between!biomass!%!N!and!litter!C:N!ratio!(adjusted!R2!=!0.32,!p!<!
0.001).!!Biomass!%N!was!a!significant!predictor!in!the!bestJfit!model!for!litter!C:N!ratios.!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
55!

!
!
!
!
!
!
!
!
!
!
8000"

Soil%C%Stock%(g%m-2)%

7000"
6000"
5000"
4000"
3000"
2000"
1000"
0"
0"

200"

400"

600"

800"

1000"

Invasive%Species%Biomass%(g%m-2)%

!
Figure!2J5.!!Regression!between!invasive!species!biomass!(cumulative!biomass!of!
Phragmites!australis,!Phalaris*arundinacea,!and*Typha!spp.)!and!soil!C!stock!(adjusted!R!=!
0.27,!p!<!0.001).!Invasive!species!biomass!was!a!significant!predictor!in!the!bestJfit!model!
for!soil!C!stock.!
!
!
!
!
!
!
!
!
!
!
!
!

56!

!
!
!
!
!
!
!
!
!
!
9000"
Ecosystem)C)Stock)(g)m/2))

8000"
7000"
6000"
5000"
4000"
3000"
2000"
1000"
0"
0"

100"

200"

300"

400"

500"

600"

Invasive)Species)Biomass)(g)m/2))

!
Figure!2J6.!!Regression!between!invasive!species!biomass!(cumulative!biomass!of!
Phragmites!australis,!Phalaris*arundinacea!and*Typha!spp.)!and!ecosystem!C!stock!
(adjusted!R2!=!0.35,!p!<!0.001).!Invasive!species!biomass!was!a!significant!predictor!in!the!
bestJfit!model!for!ecosystem!C!stock.!
!
!
!
!
!
!
!
!
!
!
!
!
57!

!
!
!
!
!
!
!
!
Phalaris HT
Phragmites HT
Typha HT
Phalaris LT
Phragmites LT
Typha LT

C-Min Rate (g CO2-C kg-1 SC day-1)

5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

5

10

15

20
25
Day of Incubation

30

35

40

Figure!2J7.!!Carbon!mineralization!rates!over!the!36Jday!laboratory!incubation.!!Repeated!
measures!ANOVA!showed!that!there!was!a!significant!3Jway!interaction!between!species,!
temperature!and!time!(F2,494!=!7.00,!p!=!0.001).!!Error!bars!represent!1!SE.!
!
!
!
!
!
!
!
!
!
!
!
!
!

58!

!

!
!
!
!
!
!
!
!
Total&C&Mineraliza.on&(g&CO23C&kg31&SC)&

120"

c
Low"Temp"(7"C)"
High"Temp"(23"C)"

100"
80"
b

60"

e

40"
20"

ae
a
d

0"
Typha&

Phalaris&
Species&

Phragmites&

!
Figure!2J8.!!Mean!cumulative!C!mineralization!over!the!36Jday!laboratory!incubation.!!The!
main!effects!of!species!(F2,8!=!5.82,!p!=!0.028)!and!temperature!(F2,47!=!1673.30,!p!<!0.001)!
were!significant,!but!not!their!interaction.!!Same!letter!superscript!denotes!nonsignificant!
differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!
!
!
59!

!
!
!
!
!
!
!

!Total!C!Mineraliza.on!(g!CO23C!kg31!SC!)!

250"
High"Temp"(23"C)"

200"

Low"Temp"(7"C)"

150"

100"

50"

0"
10"

11"

12"

13"

14"

15"

16"

17"

18"

Soil!C:N!Ra.o!

Figure!2J9.!!Regression!between!soil!C:N!ratio!and!cumulative!C!mineralization!at!high!
(21°C;!adjusted!R2!=!0.53,!p!<!0.001)!and!low!(7°C;!adjusted!R2!=!0.40,!p!<!0.001)!
temperatures.!
!
!

60!

!

2.9$
2.7$

Q10$

2.5$
2.3$
2.1$
1.9$
1.7$
1.5$
Phragmites+

Phalaris+

Typha+

Species$

!
Figure!2J10.!Comparison!of!mean!Q10!values!among!soil!collected!from!monospecific!
stands!of!Phragmites*australis,!Phalaris*arundinacea,!and!Typha!spp.!!The!effect!of!species!
was!marginally!significant!(F2,8!=!3.46,!p!=!0.082).!!Error!bars!represent!1!SE.!!!!
!
!
Net$N$Min$(mg$N$kg,1$SC)$

160"

b

140"
120"

b

100"
80"
60"

a

40"
20"
0"
Phragmites+

Phalaris+
Species$

Typha+

!
Figure!2J11.!!Comparison!of!mean!net!N!mineralization!rates!among!soil!collected!from!
monospecific!stands!of!Phragmites*australis,!Phalaris*arundinacea,!and!Typha!spp.!!The!
effect!of!species!was!significant!(F2,5!=!22.32,!p!=!0.003).!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!

61!

Discussion!
The!negative!relationship!between!invasive!species!dominance!and!Shannon!
diversity!is!a!pattern!that!has!been!found!in!investigations!at!similar!spatial!scales!(Sakai!et!
al.!2001;!Hejda!et!al.!2009),!though!the!relationship!isn’t!usually!as!strong!as!the!one!found!
in!this!wetland!survey!(Figure!2J1).!!Conversely,!Houlahan!and!Findley!(2004)!found!little!
evidence!for!invasive!species!having!a!larger!effect!than!natives!on!plant!diversity!in!58!
Ontario!inland!wetlands,!though!community!dominants!(native!or!exotic)!did!decrease!
diversity.!!When!invasive!plants!successfully!invade!they!usually!outJcompete!other!plants!
and!either!reduce!their!population!and/or!cause!them!to!go!locally!extinct!(Sakai!et!al.!
2001;!Allendorf!2003).!!This!consequence!of!invasion!usually!causes!species!diversity!to!
decline!on!a!local!scale!(though!on!larger!spatial!scales!species!diversity!can!increase!
because!at!larger!spatial!scales!those!species!that!are!threatened!at!smaller!spatial!scales!
still!persist).!!The!strong!pattern!seen!in!this!study!likely!is!partly!due!to!wetlands!being!
particularly!susceptible!to!invasion!due!to!their!hydrogeomorphic!placement!on!the!
landscape!that!results!in!high!levels!of!disturbance,!nutrient!enrichment,!and!propagule!
pressure!(Zedler!and!Kercher!2004).!!Additionally,!wetland!invasive!species!are!known!to!
form!monospecific!stands,!which!reduce!local!diversity!to!an!even!greater!extent.!
!

While!I!found!some!support!for!my!prediction!that!there!will!be!a!positive!

correlation!between!the!degree!of!invasion!and!the!overall!plant!community!NUE!(Figure!
2J2),!this!pattern!was!driven!entirely!by!LLP!(site!dominated!by!Phragmites).!!The!lack!of!a!
relationship!is!somewhat!surprising!because!wetland!invasive!species!are!known!to!usually!
produce!greater!amounts!of!biomass!than!natives!(Ehrenfeld!2003;!Liao!et!al.!2008)!and,!
therefore,!either!have!higher!NUE!or!are!using!a!larger!N!pool!than!natives.!!My!results!
suggest!the!latter!and!could!be!connected!to!the!their!ability!to!respond!to!larger!N!pools!
62!

than!natives!(Davis!et!al.!2000)!that!are!more!adapted!to!low!N!conditions!(Daehler!2003),!
though!not!always!(Funk!and!Vitousek!2007).!!While!there!have!been!similar!studies!
investigating!NUE!of!invasive!species!(Funk!and!Vitousek!2007),!this!is!the!first,!that!I!am!
aware!of,!that!has!looked!at!the!NUE!of!the!entire!community.!!Future!studies!should!
investigate!the!N!pools!used!by!wetland!invasive!species!compared!to!native!plants!to!
determine!if!invasive!species!do!use!a!larger!N!pool!than!natives.!
!

The!most!parsimonious!model!for!biomass!C!stock!included!both!invasive!and!

native!species!dominance,!though!neither!had!a!significant!relationship!with!biomass!C!
stock.!!The!relationship!between!biomass!C!stock!and!invasive!species!dominance!is!
reasonable!because!invasive!species!are!usually!high!biomass!producing!species!(Ehrenfeld!
2003;!Liao!et!al.!2008),!so!the!more!dominant!they!are!the!more!C!should!be!in!
aboveground!biomass.!!The!positive!influence!of!native!species!dominance!is!harder!to!
explain,!but!could!indicate!that!species!identity!(invasive!or!native)!didn’t!truly!matter.!!
Total!biomass!was!the!best!predictor!of!biomass!N!stock!suggesting!that!regardless!of!
community!composition!(native!or!invasive),!wetlands!with!more!biomass!also!had!more!N!
stored!in!the!aboveground!biomass.!!This!is!further!evidence!for!invasive!species!not!
having!a!higher!NUE!than!native!species!because!otherwise!there!would!likely!not!be!a!
relationship!between!total!biomass!and!biomass!N!stocks!as!invasive!species!constitute!the!
majority!of!the!biomass!at!most!of!these!sites.!
!

The!bestJfit!models!for!litter!C!and!N!stocks!contained!tissue!chemistry!predictors!

with!biomass!%N!and!C:N!ratios!having!a!positive!effect!and!biomass!%C!a!negative!effect.!!
These!individual!variables!were!not!significant,!however,!and!for!litter!N!stock!there!was!
not!a!statistical!significance!between!the!bestJfit!model!and!the!null!model,!so!while!tissue!

63!

chemistry!traits!likely!do!influence!litter!C!and!N!stocks,!in!this!data!set!it!is!hard!to!have!
confidence!in!their!importance.!!The!most!parsimonious!model!for!litter!C:N!ratio!had!both!
native!species!and!biomass!%N!as!predictor!variables,!though!only!biomass!%N!was!
significant.!!As!mentioned!in!the!results!section,!the!negative!relationship!found!between!
litter!C:N!ratio!and!biomass!%N!(as!biomass!%N!increases,!litter!C:N!ratio!decreases)!
shows!the!link!between!living!biomass!nutrient!concentrations!and!the!litter!quality;!the!
living!biomass!N!content!influenced!the!litter!by!increasing!the!quality!(lowering!the!C:N!
ratios)!as!N!content!increased.!!The!link!between!living!tissue!chemistry!and!litter!quality!is!
a!logical!relationship!but!has!not!been!shown!before!at!the!community!level!as!in!this!
study,!though!it!has!been!inferred!(Wardle!et!al.!2004).!!The!lack!of!invasive!species!
influence!on!litter!C!and!N!stocks!and!quality!refuted!predictions!2.2!and!3.1,!and!showed!
that,!as!a!whole,!invasive!species!don’t!differ!from!natives!in!their!ability!to!alter!litter!
stocks!and!quality.!!This!conclusion!is!supported!by!HerrJTuroff!and!Zedler!(2005)!that!
found!that!Phalaris!invasion!did!not!alter!a!wetland’s!ability!to!retain!N.!!It!should!be!stated,!
though,!that!the!litter!collected!in!the!wetland!survey!was!litter!that!had!accumulated!on!
the!soil!surface!over!multiple!growing!seasons!and!therefore!might!not!be!an!indicator!of!
fresh!litter!quality.!
Though!the!full!model!was!the!bestJfit!model!for!soil!C!stocks,!only!invasive!species!
biomass!and!litter!mass!were!significant.!!The!positive!influence!invasive!species!had!on!
soil!C!stocks!supports!hypothesis!3!that!as!the!dominance!of!invasive!species!increases!so!
will!the!organic!matter!storage!of!the!wetlands!they!invade!(Figure!2J5).!!This!relationship!
was!also!seen!in!a!metaJanalysis!by!Liao!et!al.!(2008)!that!found!invasive!species!increased!
root!C!stock!by!5%!and!shoot!C!stock!by!133%.!!Additionally,!He!et!al.!(2011)!found!that!

64!

Phalaris!had!a!greater!seasonal!C!gain!compared!to!the!native!species!Carex*stricta.!The!
negative!influence!of!litter!mass!seems!counterintuitive!as!more!litter!mass!should!mean!
more!organic!matter!being!incorporated!into!the!soil,!but,!as!mentioned!above,!the!litter!
collected!in!the!wetland!survey!was!litter!that!had!accumulated!on!the!soil!surface!over!
multiple!growing!seasons.!!The!accumulation!of!the!litter!may!be!due!to!the!recalcitrance!of!
the!litter,!i.e.,!lower!quality!litter!resisted!decomposition!and!thus!was!not!added!to!the!soil!
C!stocks.!!The!negative!relationship!found!between!litter!mass!and!soil!N!stocks!follows!the!
same!logic!used!for!its!same!relationship!found!with!soil!C!stocks.!!As!for!the!negative!
relationship!between!native!species!biomass!and!soil!and!ecosystem!N!stocks,!this!could!be!
caused!by!native!species!having!lower!detrital!N!concentrations!or!could!be!a!function!of!
native!species!producing!less!biomass!than!invasives.!!Therefore,!wetlands!that!are!more!
dominated!by!natives!produce!less!biomass,!and!since!biomass!N!stocks!was!a!function!of!
total!biomass!in!this!study,!those!wetlands!might!have!less!organic!N!inputs!(Ehrenfeld!
2003).!
The!positive!relationship!between!litter!%N!and!soil!C:N!ratios!seems!
counterintuitive!if!litter!N!was!directly!incorporated!into!soil!OM!as!in!Melillo!et!al.!(1989)!
because!one!would!expect!soil!C:N!ratio!to!decrease!as!litter!with!higher!N!content!was!
incorporated!into!the!soil.!!Similar!to!the!effects!of!litter!mass!on!soil!C!and!N!stocks,!this!
relationship!could!be!caused!by!the!litter!collected!in!this!study!having!accumulated!over!
multiple!years,!so!it!is!possible!that!having!higher!litter!%N!might!be!indicative!of!N!being!
locked!up!in!litter!and!not!being!incorporated!into!the!soil!or!N!immobilization!in!the!litter!
(Melillo!et!al.!1989).!!!

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!

For!ecosystem!C!stocks,!invasive!species!had!a!positive!influence!on!the!C!storage!

within!the!wetlands!surveyed!in!this!study!(Figure!2J6).!!This!is!in!support!of!hypothesis!3!
and!suggests!that!invasive!plant!species!play!an!important!role!in!the!ecosystem!
functioning!of!temperate!wetlands.!!Due!to!the!nature!of!this!survey!study,!the!exact!
mechanisms!by!which!invasive!species!were!affecting!wetland!C!storage!is!unknown,!but!
there!is!evidence!from!the!controlling!factors!of!the!other!C!and!N!stocks!in!this!study!that!
plant!traits!such!as!biomass!N!concentration!and!litter!quality!could!be!important.!!Since!
there!wasn’t!an!effect!of!invasive!species!on!litter!C!and!N!stocks!or!quality,!invasive!
species!may!be!influencing!soil!and!ecosystem!C!stocks!by!greater!belowground!biomass!
production!than!natives!(Liao!et!al.!2008).!!Many!studies!have!found!that!Phragmites,*
Phalaris,!and!Typha!spp.!produce!more!belowground!biomass!(and!overall!biomass)!than!
natives!(Green!and!Galatowitsch!2001!and!2002;!Vymazal!and!Kropfelova!2005).!
Understanding!how!wetlands!function!changes!following!invasions!is!critical!if!we!are!to!
properly!manage!these!nearly!ubiquitous!invasions,!and!if!there!is!a!positive!aspect!to!
invasion,!such!as!increase!C!storage,!then!this!needs!to!be!considered!when!determining!
management!for!invasive!wetland!species.!!More!detailed!research!is!needed!to!determine!
the!degree!and!mechanism!of!this!apparent!relationship.!
While!the!cumulative!effect!of!invasive!wetland!plant!species!(Phragmites,!Phalaris,!
and!Typha)!were!shown!in!this!study,!their!differences!in!key!plant!traits,!such!as!litter!
quality,!is!important!to!elucidate!as!these!species!likely!have!unique!individual!effects!on!C!
and!N!cycling!(Eviner!2004).!!The!results!of!the!carbon!quality!incubation!clearly!showed!
that!there!are!differences!in!C!mineralization!rates!from!soil!collected!within!monospecific!
stands!of!each!of!these!species!(Figure!2J8),!which!is!in!support!of!hypothesis!4.!!Soil!

66!

collected!under!populations!of!Phalaris!had!the!greatest!C!mineralization!rates,!followed!by!
Typha!and!then!Phragmites.!!This!suggests!that!the!OM!in!Phalaris!soil!was!the!most!labile!
of!the!three!species!and!this!lability!can!be!connected!to!Phalaris!having!the!highest!quality!
soil!and!litter,!while!Phragmites!had!the!lowest!quality!soil!and!litter.!!The!difference!among!
these!invasive!species!in!litter!quality!could!also!explain!why!there!was!not!a!clear!
relationship!between!invasive!species!biomass!and!litter!quality!in!the!wetland!survey.!!
The!importance!of!soil!quality!on!decomposition!was!further!illustrated!by!the!strong!
relationship!between!soil!C:N!ratio!and!total!C!mineralization,!which!was!stronger!at!high!
temperatures!than!at!low!temperatures.!!The!relationship!between!OM!quality!(C:N!ratios)!
and!C!mineralization!has!been!shown!in!other!studies!(Melillo!et!al.!1982;!Taylor!et!al.!
1989;!Xu!and!Hirata!2005;!Parton!et!al.!2007),!and!further!supports!the!role!soil!quality!on!
decomposition.!!The!difference!between!temperatures!is!likely!caused!by!greater!microbial!
activity!at!higher!temperatures!that!probably!enhances!the!controlling!effect!of!the!quality!
of!the!organic!matter.!!!
Though!the!difference!among!species!in!the!Q10!response!was!only!marginally!
significantly!different!(Figure!2J10),!because!Typha!soil!had!the!lowest!Q10!value!(2.13)!
and!thus!was!the!most!resistant!to!the!effects!of!temperature!change,!Typha!monospecific!
stands!may!be!less!altered!by!a!warming!climate,!though!the!difference!among!species!was!
minimal.!!The!range!of!Q10!values!among!studies!species!(2.13!to!2.47)!fell!within!the!range!
of!1.6!to!4.8!found!for!wetland!soils!(Nieveen!et!al.!1998;!Bubier!et!al.!2003;!Lafleur!et!al.!
2005)!and!the!Q10!for!Phragmites,!2.47,!was!very!close!to!what!Zhou!et!al.!(2009)!found!
(2.38)!for!soil!collected!within!monospecific!stands!of!Phragmites!in!Northeast!China.!!In!

67!

comparison!to!other!ecosystems,!the!range!I!found!in!the!study!species!was!similar!to!what!
Bekku!et!al.!(2003)!found!for!temperate!(2.9),!tropic!(2.1)!and!arctic!(3.4)!soils,!though!
arctic!soils!were!about!1!Q10!greater!than!Phragmites!monospecific!stands.!!!!
Phalaris!soil!had!the!highest!N!mineralization!and!nitrification!rates,!which!
corresponded!with!Phalaris!soil!having!the!highest!C!mineralization!rates!(Figure!2J11).!!
This!showed!that!Phalaris!soil!was!more!active!in!these!laboratory!incubations!compared!
to!Typha!and!Phragmites,!giving!further!support!to!hypothesis!4.!!N!mineralization!rates!
were!not!correlated!with!soil!C:N!ratio!and,!additionally,!soil!%C!and!%N!did!not!match!
those!found!for!the!C!quality!incubation!for!two!reasons:!(1)!soil!used!in!the!C!quality!
incubation!was!collected!from!a!5!cm!depth!and!soil!used!in!the!N!mineralization!
incubation!was!collected!from!a!10!cm!depth!and!(2)!a!different!monospecific!stand!of!
Phragmites!was!used!in!place!of!NLCLP!that!had!much!greater!soil!%C.!!Specifically,!using!a!
deeper!soil!core!could!have!incorporated!more!mineral!material!and!thus!decrease!soil!%C!
and!%N!as!seen!in!comparing!the!soil!from!the!two!incubations!(Tables!2J8!and!2J10).!!
Similar!to!these!results,!Bridgham!et!al.!(1998)!found!that!N!mineralization!varied!greatly!
across!an!ombrotrophicJminerotrophic!gradient!in!northern!Minnesota!and!that!the!
dominant!wetland!community!had!strong!direct!and!indirect!effects.!!!
The!C!and!N!mineralization!rates!differences!among!species!appear!to!be!a!
consequence!of—or!at!least!correlated!with—differences!in!plant!traits,!such!as!litter!
quality.!!Though!it!was!useful!to!look!at!the!cumulative!effects!of!these!invasive!species,!it!is!
just!as!important!to!be!aware!of!their!speciesJspecific!differences!to!better!understand!
their!individual!effects.!!Species!differences!are!known!to!influence!many!aspects!of!
ecosystem!functioning!(Eviner!and!Chapin!2003;!Wardle!et!al.!2004)!and!these!differences!
68!

can!be!especially!important!when!determining!the!effects!of!species,!like!invasive!species,!
that!can!dominate!large!spatial!areas,!like!wetlands,!that!are!“hot!spots”!for!biogeochemical!
cycling.!!
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Chapter(3(
Effects(of(Aboveground(Biomass(and(Litter(on(Biogeochemical(Cycling(in(Phragmites)
australis(Stands(
!
Brief(Rationale(
!
The!results!from!Chapter!2!showed!that!invasive!species!have!an!effect!on!C!and!N!
stocks!and!organic!matter!quality,!and!that!these!effects!likely!differ!among!the!three!
invasive!species!studied!(Phragmites*australis,!Phalaris*arundinacea,!and!Typha*spp.).!!
While!only!two!sites!were!dominated!by!P.*australis*(hereafter!Phragmites)!in!the!wetland!
survey,!those!sites!had!the!most!biomass!and!soil!organic!matter!of!all!sites!surveyed.!!
Additionally,!speciesJspecific!investigation!into!soil!and!litter!quality!showed!that!soil!
beneath!monospecific!stands!of!Phragmites!had!high!soil!C:N!ratios!(low!quality)!and!
decomposed!more!slowly!compared!to!those!dominated!by!P.*arundinacea!and!Typha!spp..!!
It!is!therefore!critical!to!investigate,!in!more!detail,!the!mechanisms!by!which!Phragmites!
alters!the!wetlands!it!invades!due!to!its!large!and!expanding!distribution!in!the!United!
States.*
Phragmites!is!a!cosmopolitan!wetland!species!found!on!all!continents!except!
Antarctica!(Cronk!and!Fennessy!2001).!!In!some!areas!of!Europe,!Phragmites!is!in!decline!
and!wetland!restoration!and!management!have!focused!on!increasing!its!presence!and!
spread.!!In!North!America,!Phragmites!was!only!a!minor!component!of!wetland!vegetation!
for!thousands!of!years,!but!is!now!one!of!the!most!aggressive!wetland!invaders!in!the!
United!States!(Chambers!et!al.!1999).!!The!spread!of!the!aggressive!genotype!is!attributed!
to!multiple!European!introductions!along!the!northern!Atlantic!coast!in!the!19th!century!
(Plut!et!al.!2011).!!Though!the!exact!origin!of!the!invasive!genotype!is!not!known,!recent!
evidence!suggests!the!United!Kingdom!as!the!most!likely!source!(Plut!et!al.!2011).!!This!

70!

genotype!is!salt!tolerant!and!can!maintain!horizontal!clonal!growth!(up!to!4.5!meters!per!
year)!allowing!it!to!establish!and!spread!in!coastal!wetlands!displacing!native!plants,!such!
as!Spartina!spp.!!Once!established!on!the!east!coast,!the!European!genotypes!quickly!spread!
and!are!now!found!in!all!48!conterminous!states!(Chambers!et!al.!1999).!!The!native!
genotype!is!much!less!aggressive!than!the!exotic,!which!is!now!outcompeting!native!
Phragmites,!as!well!as!most!other!wetland!plants!in!sites!where!it!becomes!established!
(Plut!et!al.!2011).!!!
Its!capacity!for!horizontal!growth!and!salt!tolerance!makes!roadside!ditches!in!
northern!climates,!where!road!deicing!salts!are!used,!ideal!environments!for!invasion!and!
spread.!!Phragmites!can!grow!to!heights!of!4J5!meters!allowing!it!to!outcompete!most!
wetland!plants!for!light.!!Additionally,!the!standing!dead!stems!of!Phragmites!usually!resist!
decomposition!and!persist!in!wetlands!for!years!(Graneli!1990;!Schieferstein!1997;!
Gessner!2001).!!The!large!amount!of!litter!produced!every!year!shades!the!soil!surface!
further!restricting!competitors’!access!to!light.!!In!addition!to!the!effects!Phragmites!can!
have!to!the!native!plant!community!(and!other!trophic!levels),!it!can!also!impact!nutrient!
cycling.!!Otto!et!al.!(1999)!showed!that!inorganic!N!availability!was!higher!in!Phragmites!
stands!compared!to!Lythrum*salicaria!and!Typha*angustifolia!stands,!while!Findlay!et!al.!
(2002)!found!detrital!N!standing!stocks!were!greater!in!populations!of!Phragmites!versus!
T.*angustifolia.!!!The!presence!of!Phragmites!usually!leads!to!organic!matter!buildup,!which!
can!change!not!only!the!C!storage!of!the!wetland,!but!the!hydrology!as!well!(Able!et!al.!
2003).!!While!the!above!studies!have!been!able!to!show!effects!of!Phragmites!invasion!on!
biogeochemical!cycling,!few!studies!have!tried!to!elucidate!the!mechanisms!of!change.!!It!
has!been!shown!that!radial!oxygen!loss!(ROL),!the!loss!of!oxygen!through!the!rooting!

71!

system!of!emergent!wetland!plants,!is!important!for!the!health!and!survival!of!Phragmites*
(Armstrong!and!Armstrong!2001;!Colmer!2003;!Soukup!et!al.!2007),*and!it!is!possible!that!
this!oxygen!release!in!the!rooting!zone!could!have!impacts!on!biogeochemical!cycling!by!
creating!oxidizing!conditions!in!an!otherwise!anaerobic!environment.!!!
It!is!important!to!understand!the!mechanisms!by!which!Phragmites!alters!the!biotic!
and!abiotic!environment!because!then!we!may!be!able!to!predict!the!consequences!of!
Phragmites!invasion!and!possibly!invasions!by!other!species!with!similar!traits,!as!well!as!
to!better!manage!their!impact.!!For!example,!if!it!is!found!that!the!litter!of!Phragmites!
significantly!reduces!light!levels!at!the!soil!surface,!then!the!practice!of!killing!stands!with!
glyphosate!and!then!leaving!the!litter!standing!might!not!be!advantageous!because!of!the!
negative!effects!low!light!levels!could!have!on!native!recruitment.!!One!way!to!determine!
these!mechanisms!is!to!manipulate!both!the!litter!and!biomass!in!a!field!experiment!and!
then!monitor!both!the!abiotic!environment!and!C!and!N!cycling!within!manipulated!plots.!
!
Objectives,(Hypotheses,(and(Predictions(
Objective:!To!determine!the!mechanisms!by!which!Phragmites!influences!ecosystem!
function!in!the!field.!!Phragmites!invasion!is!likely!to!cause!changes!to!the!soil!
microenvironment!(e.g.,!temperature,!redox!potential,!etc)!due!to!the!high!production!of!
biomass,!with!ramifications!for!soil!microbial!activity!and!biogeochemical!processes,!such!
as!N!and!C!cycling,!but!also!plant!available!cations!and!anions.!!Such!changes!are!important!
to!understand!the!full!impact!of!Phragmites!invasion,!as!well!as!attempted!eradication.!
(
Hypothesis:!Phragmites!exerts!both!direct!and!indirect!influences!on!biogeochemistry;!

72!

direct!effects!include!plant!nutrient!uptake!into!live!biomass!and!indirect!effects!include!
changes!in!the!soil!microenvironment!and!in!OM!matter!input!quality!and!quantity.!!As!a!
result,!I!predict!the!following:!
!
•!Removal!of!Phragmites!litter!will(increase!light!levels!to!the!soil!surface,!which!will!
result!in!increased!diurnal!maximum!soil!temperature,!though!living!biomass!
should!still!shade!soil.!!Increased!temperature!will!enhance!in*situ!N!mineralization!
and!decomposition!rates!compared!to!reference!plots.!!Cessation!of!litter!inputs!also!
will!decrease!OM!quality!of!the!soil!as!the!labile!OM!pool!is!mineralized!and!not!
replenished!to!the!same!degree!as!in!the!reference!plots,!though!effects!on!OM!
quality!likely!would!take!more!than!a!few!years!to!become!detectable.!
•!Removal!of!living!biomass(will!increase!light!levels!to!the!soil!surface,!which!will!
result!in!increased!diurnal!maximum!soil!temperature,!though!the!litter!layer!should!
still!provide!partial!shading!of!the!soil.!!Increased!temperature!should!enhance!in*
situ!N!mineralization!and!decomposition!rates!compared!to!reference!plots.!!
Reduced!N!and!other!plant!nutrient!uptake!by!vegetation!should!increase!their!soil!
pore!concentration.!!Additionally,!the!sediment!anoxic!zone!should!increase!due!to!a!
reduction!in!radial!oxygen!loss!from!rooting!system.!
•!Because!the!total!removal!treatment!was!initiated!in!2010,!a!soil!organic!matter!
effect!would!probably!take!years!to!become!detectable.!!!This!treatment!was!mainly!
established!to!determine!light!levels!and!temperature!in!the!absence!of!both!litter!
and!vegetation.!!The!total!removal!of!both!the!living!biomass!and!litter!of!Phragmites!
should!result!in!the!greatest!increase!in!light!levels!to!the!soil!surface,!which!will!
73!

result!in!increased!diurnal!maximum!soil!temperature.!!This!increased!temperature!
should!enhance!in*situ!N!mineralization!and!decomposition!rates!compared!to!all!
other!treatments,!but!the!greatest!difference!should!be!when!compared!to!reference!
plots.!!
!
Methods(
!
Site*description*and*experimental*treatment*design*
!
I!conducted!a!field!experiment!that!manipulated!aboveground!biomass!and!litter!
levels!in!three!temperate!wetlands.!!The!experiment!was!designed!to!quantify!the!direct!
and!indirect!effects!of!Phragmites*on!the!soil!microenvironment!and!biogeochemical!
cycling.!!!Three!sites!were!selected!in!2008!that!were!monospecific!stands!of!Phragmites*of!
similar!size!(see!below);!two!sites!were!located!within!Lake!Lansing!Park!in!central!lower!
Michigan!(Figure!3J1;!42o46’07”N!85o23’32”W);!a!third!site!was!located!within!a!wetland!
environment!surrounding!Glasby!Lake!in!southwestern!Michigan!(Figure!3J2;!42o28’52”N!
85o25’02”W).!!!
Lake!Lansing!Park!is!embedded!in!a!mosaic!of!lakes,!woodlots,!and!residential!areas.!!
The!total!area!of!the!park!is!166!hectares!and!consists!mainly!of!deciduous!forest,!
coniferous!forest,!and!a!large!interconnected!wetland!complex!of!approximately!80!
hectares.!!The!park!has!been!extensively!invaded!by!a!variety!of!invasive!plant!species,!
including!Phragmites,*P.*arundinacea,!and!Typha × glauca.!!The!wetland!complex!contains!a!
mosaic!of!monospecific!stands!of!these!three!species,!though!some!areas!are!mixtures!of!

€
these!along!with!some!native!species.!!Some!of!the!more!conspicuous!native!species!include!
Carex!spp.,!Juncus!spp.,!Sambucus!spp.,!Leersia*oryzoides,!Eutrochium*maculatum,*Impatiens*
spp.,!and!Asclepias*incarnata.!!Both!LLP!sites!consisted!of!pure!stands!of!Phragmites!of!a!
74!

total!area!less!than!1!hectare.!!LLP1!was!located!within!an!inlet!of!the!major!wetland!
complex!that!dominates!the!park,!while!LLP2!was!separated!from!the!major!wetland!
complex!by!areas!of!higher!elevation!and!a!gravel!road.!!Due!to!this!spatial!separation!and!
different!hydrology!(see!results)!these!two!sites!were!considered!independent.!!
Subsequent!to!the!completion!of!this!research,!beginning!in!2011,!the!LLP!sites!were!
subjected!to!control!measures!intended!to!eradicate!Phragmites!from!within!the!park.!!
The!experimental!wetland!site!adjacent!to!Glasby!Lake!(referred!to!hereafter!as!
Glasby)!was!similar!in!size!to!LLP1!and!LLP2!with!other!invasive!species!such!as!P.*
arundinacea!and!T.! × glauca!surrounding!the!Phragmites!stand,!comparable!to!the!LLP!
sites.!!The!region!around!Glasby!Lake!lies!on!a!glacial!landscape!and!has!abundant!wetland!

€
cover!(~!10%)!with!low!levels!of!residential!development!in!a!landscape!dominated!by!
forests,!rowJcrop!agricultural!fields,!and!abandoned!fields.!!Glasby!Lake!itself!is!
approximately!10!hectares!of!open!water!with!more!extensive!wetlands!surrounding!the!
lake.!!The!amounts!of!live!and!dead!Phragmites!biomass,!as!well!as!soil!and!water!
characteristics,!at!these!three!sites!are!compared!in!Table!3J1.!!The!data!for!Table!3J1!were!
collected!over!the!growing!seasons!of!2008J2010!and!the!methodology!used!to!collect!the!
field!data!can!be!found!in!Appendix!B.!
To!separate!the!effects!of!living!vegetation!versus!litter!on!the!soil!microenvironment!
and!biogeochemical!cycling,!experimental!manipulation!of!litter!and!aboveground!living!
biomass!(AGB)!was!initiated!in!the!summer!of!2008.!!At!each!of!the!three!sites!described!
above,!I!created!ten!2!x!2!m!(4!m2)!plots!randomly!distributed!throughout!the!site,!and!
assigned!each!plot!to!either!a!reference,!an!AGB!removal,!a!litter!removal,!or!a!total!
removal!treatment!(n=3!for!all!treatments!except!n=1!for!total!removal!treatment).!!I!
75!

marked!the!corner!of!each!with!PVC!that!stood!1!m!from!the!soil!surface!for!three!corners!
of!the!plot!and!3!m!for!the!fourth!corner.!!These!ten!plots!were!randomly!established!
within!each!site!and!then!each!plot!was!randomly!assigned!a!treatment.!!Vegetation!was!
cleared!around!each!plot!(0.5!m)!to!establish!a!buffer!zone!and!no!experimental!samples!
(except!for!AGB)!were!collected!within!20!cm!from!the!outer!edge!of!the!plot!to!reduce!
edge!effects.!!The!height!of!these!stands!exceeded!3!m!and!thus!the!buffer!zone!had!little!
effect!on!light!penetration!to!the!ground!surface.!Reference!and!biomass!removal!plots!
were!established!at!the!beginning!of!the!growing!season!in!2008,!litter!removal!plots!at!the!
beginning!of!growing!season!in!2009,!and!total!removal!plots!at!the!beginning!of!the!
growing!season!in!2010.!!!
For!AGB!removal!treatment!plots,!all!individual!plants!were!cut!at!the!soil!surface!and!
removed!from!the!plot!(standing!and!fallen!litter!remained).!!For!litter!removal!treatment!
plots,!all!standing!and!fallen!litter!was!collected!by!hand!and!removed!from!the!plot!(AGB!
remained).!!For!the!total!removal!plots,!all!AGB!and!litter!(standing!and!fallen!litter)!was!
removed!by!hand.!!Total!removal!plots!were!established!to!determine!light!levels!and!
temperature!in!the!absence!of!both!litter!and!vegetation.!!Litter!and!AGB!were!not!altered!
in!the!reference!plots.!!Manipulations!were!maintained!every!three!weeks!during!the!
growing!season!(May!to!October)!by!removing!any!vegetation!regrowth!from!the!AGB!
removal!plots!and!any!newly!fallen!litter!in!the!litter!removal!plots.!!In!the!fall!of!2009,!all!
of!the!senesced!AGB!in!the!litter!removal!plots!was!cut!at!the!soil!surface!and!moved!to!the!
AGB!removal!plots!to!prevent!any!litter!deposition!in!litter!removal!plots,!as!well!as!to!
ensure!the!AGB!removal!plots!continued!to!receive!litter!inputs.!!Monitoring!of!the!
reference!and!manipulation!plots!started!in!growing!season!of!2008!(May)!and!continued!

76!

through!the!growing!season!of!2009!and!ended!past!the!growing!season!of!2010!
November).!!While!root!decay!may!have!occurred!in!the!AGB!removal!plots,!because!
regrowth!from!rhizomes!persisted!throughout!the!growing!season,!it!is!unlikely!that!
substantial!root!decomposition!occurred.!!Regardless,!roots!and!rhizomes!were!removed!
from!soil!cores!collected!for!assays!that!might!be!influenced!by!root!decay,!e.g.,!for!the!in*
situ!N!mineralization!assay.!!!
!
Abiotic*and*biotic*measurements!!!!
To!monitor!water!table!levels,!Solinst!pressure!transducers!were!installed!at!each!site!
along!with!Solinst!barometric!pressure!loggers!to!correct!for!atmospheric!pressure.!!
Pressure!transducers!were!suspended!within!a!~1.5Jm!long!PVC!pipe!with!holes!drilled!
through!the!sides!to!allow!water!to!enter!the!pipe.!!PVC!pipes!where!surrounded!with!a!
small!mesh!size!material!to!keep!soil!and!debris!from!entering.!!Pressure!transducers!
within!the!PVC!structure!were!installed!in!a!randomly!selected!plot!1!m!below!the!
soil/sediment!surface.!!Pressure!transducers!were!installed!in!early!summer!of!2008,!2009,!
and!2010!and!removed!in!late!October!each!year!to!avoid!winter!damage!and!to!download!
data.!!Water!table!measurements!in!2008!were!taken!only!at!LLP1!and!Glasby.!!Manual!
water!level!measurements!were!also!taken!at!each!plot!every!third!week!of!the!growing!
season.!!All!plots!experienced!relatively!similar!hydrologic!conditions!within!a!site,!
therefore!it!is!possible!to!compare!site!hydrologic!conditions!based!on!pressure!transducer!
measurements!at!a!single!point.!!!!
To!determine!treatment!effects!on!soil!characteristics,!soil!samples!were!collected!at!
each!plot!at!the!end!of!the!growing!season!and!analyzed!for!bulk!density,!%!moisture,!and!

77!

%C!and!N!to!determine!C!and!N!storage.!!Surface!soil!was!sampled!to!a!10!cm!depth!using!a!
soil!corer (246!cm3)!and!samples!were!transported!to!the!lab!on!ice!and!kept!at!4°C!until!
processed!(~!3!days).!!For!processing,!soils!were!sieved!(4!mm),!subJsampled!for!bulk!
density!and!gravimetric!water!content!(GWC)!determination,!and!then!dried!to!a!constant!
mass!at!80°C.!!Dried!soils!were!then!ground!and!homogenized!using!a!mortal!and!pestle!
and!run!on!an!elemental!combustion!system!(Costech!ECS!4010,!Valencia,!CA)!for!%C!and!
%N!analysis.!!Samples!were!run!in!duplicate!with!atropine!used!as!a!standard!every!10!
samples.!!For!the!soil!samples!collected!in!2010,!the!10!cm!soil!cores!were!split!into!two!
depths,!0J5!cm!and!5J10!cm,!and!analyzed!separately,!including!for!NH4+!+!NO3J!
concentration!(see!N!mineralization!and!nitrification!methods!below)!to!determine!
possible!depth!effects.!
!

Surface!water!samples!were!taken!on!a!monthly!basis!during!the!2009!and!2010!

growing!seasons!as!baseline!data!to!compare!among!sites!and!to!determine!treatment!
effects!on!water!chemistry!(Table!3J1).!!These!three!sites!varied!seasonally!and!among!
years!in!the!presence!and!depth!of!water!above!the!soil!surface.!!Water!samples!were!
collected!when!standing!water!was!greater!than!5!cm!using!a!250!ml!polyethylene!bottle!
submerged!below!the!water!surface.!!Samples!were!analyzed!for!soluble!reactive!
phosphorus!(SRP),!ammonium,!total!alkalinity,!dissolved!organic!carbon!(DOC),!and!other!
major!cations!and!anions!(NO3J,!ClJ,!Na+,!Mg2+,!Ca2+,!K+).!!Dissolved!oxygen,!specific!
conductivity!(SpC),!water!temperature,!pH,!and!oxidationJreduction!potential!(ORP)!were!
monitored!using!an!YSI!556!MultiJProbe!System.!!!
After!all!experimental!manipulations!were!established!at!the!three!Phragmites!sites,!

78!

HOBO!logging!thermistors!were!installed!(4!vertical!positions:!ambient![60!cm!above!soil!
surface],!litter!layer,!and!at!2J!and!10Jcm!soil!depths)!at!one!random!plot!per!treatment!per!
site!to!determine!if!the!experimental!treatments!affected!litter!and!soil!temperatures.!!
From!8!July!to!29!October!2010!soil!temperatures!at!six!depths!(soil!surface,!2,!10,!20,!30,!
40!cm)!were!manually!measured!with!a!Multilogger!Thermometer!(OMEGA!Engineering,!
Inc.)!at!each!treatment!plot!at!each!site.!!Manual!temperature!measurements!were!made!to!
check!the!accuracy!of!HOBO!temperature!probe!measurements,!as!well!as!for!analysis!of!
depth!profiles.!!In!summer!2010,!light!levels!(photosynthetically!active!radiation)!at!the!
ground!level!within!each!plot!were!estimated!monthly!using!an!AccuPAR!LPJ80!
Ceptometer!(ICT!International).!!!!
*
Litter*bag*decomposition*assay*
To!quantify!in*situ!decomposition!rates!a!litter!bag!assay!was!performed!using!both!
Phragmites!stem!tissue!and!Whatman!cellulose!filters!as!a!standard!substrate.!!Litter!bags!
(10!cm!x!10!cm)!were!created!using!Nylon!mesh!(mesh!size!=!0.25!mm)!and!thread.!!
Approximately!1!g!of!airJdried!Phragmites!stem!litter!was!placed!in!the!litter!bag,!along!
with!one!airJdried!Whatman!cellulose!filter!paper!(90!mm!diameter,!~!1.12!g).!!Samples!of!
the!airJdried!stem!litter!and!filter!paper!were!dried!to!a!constant!mass!at!80°C!and!
weighed,!and!the!percent!difference!was!used!to!correct!the!airJdried!weights.!!The!litter!
bags!were!then!sealed!using!a!heated!hand!impulse!sealer!with!plastic!as!the!sealant.!!Litter!
bags!were!connected!with!braided!Nylon!fishing!line!to!a!marker!flag!and!then!either!
placed!on!the!soil!surface!or!10!cm!below!the!soil!surface.!!Five!litter!bags!were!placed!in!
each!plot,!three!on!the!soil!surface!and!two!at!10!cm!below!the!soil!surface!(total!=!150!

79!

litter!bags:!90!at!soil!surface,!60!at!10!cm!soil!depth).!!Litter!bags!were!installed!in!each!plot!
on!29!July!(Glasby)!and!30!July!(LLP1!and!LLP2)!in!2010.!!After!18!days!in!the!field,!one!
randomly!selected!soil!surface!litter!bag!was!removed!from!each!plot,!returned!to!the!lab,!
and!kept!at!4°C!until!processed.!!After!a!total!of!42!and!90!days!in!the!field,!one!surface!and!
one!buried!litter!bag!were!removed!(randomly!selected),!returned!to!the!lab,!and!kept!at!
4°C!until!processed.!!During!the!time!the!litter!bags!were!in!the!field,!water!levels!were!~!
19!cm!above!the!soil!surface!at!Glasby,!55!cm!below!the!soil!surface!at!LLP1!and!fell!from!5!
cm!above!the!soil!surface!to!below!the!soil!surface!at!LLP2.!!For!processing,!litter!bags!were!
gently!washed!with!distilled!water!to!remove!the!majority!of!the!soil!particles.!!The!
cellulose!filter!was!separated!from!the!stem!litter,!placed!in!aluminum!foil,!dried!to!a!
constant!mass!at!80°C!and!weighed.!!
!!!
Porewater*equilibrators!
To!investigate!possible!treatment!effects!on!the!chemistry!of!water!in!the!root!zone,!
porewater!equilibrators!were!installed!at!each!site!for!approximately!20!days,!from!11!
August!(Glasby),!12!August!(LLP2),!and!16!August!(LLP1)!2011!to!31!August,!1!September,!
and!2!September!2011,!respectively.!!At!Glasby!and!LLP2,!a!porewater!equilibrator!was!
installed!at!one!randomly!selected!reference,!AGB!removal,!and!litter!removal!treatment!
plot.!!At!LLP1,!due!to!low!water!table!levels,!porewater!equilibrators!were!only!installed!at!
a!reference!and!AGB!removal!plot.!!The!porewater!equilibrators!were!constructed!out!of!
clear!acrylic!plastic!with!a!total!length!of!60!cm!and!width!of!10!cm.!!Fourteen!paired!wells!
ran!from!top!to!bottom!of!the!porewater!equilibrator!(3.5!cm!distance!between!well!pairs)!
with!each!well!holding!12!ml!of!water.!!Before!installation,!each!porewater!equilibrator!was!

80!

submerged!in!filtered!water!(Pall!Supor!450!membrane)!and!one!BiotransTM!nylon!
membrane!(0.2!µm!pore!size)!filter!membrane!sheet!was!laid!on!top!of!the!porewater!
equilibrator,!covering!the!wells.!!The!faceplate!was!then!securely!fastened!to!seal!the!
membrane!over!the!well!openings.!!Each!porewater!equilibrator!was!then!placed!in!a!
vertical!acrylic!tank!filled!with!filtered!water!and!deoxygenated!overnight!by!pumping!N2!
gas!through!a!bubbler!into!the!bottom!of!the!tank!for!approximately!12!hours.!!Tanks!
containing!the!porewater!equilibrators!were!then!transported!in!deoxygenated!water!to!
each!site.!!For!installation,!porewater!equilibrators!were!driven!into!the!soil!until!only!the!
top!two!well!pairs!were!above!the!soil!surface!in!the!surface!water!(LLP2!and!Glasby).!!Due!
to!low!water!table!levels,!installation!at!LLP1!included!digging!a!pilot!hole!to!determine!the!
location!of!the!water!table!and!then!installing!the!porewater!equilibrator!to!that!depth.!!!
After!approximately!20!days!in!the!field,!porewater!equilibrators!were!removed!and!
analyzed!for!total!dissolved!P,!NO3J,!ClJ,!Na+,!Mg2+,!Ca2+,!K+!and!silicate.!!
!
N*mineralization*and*nitrification*assays!
In!the!summer!of!2010,!in*situ!net!N!mineralization!and!nitrification!rates!were!
assayed!in!each!plot!using!the!buried!polyethylene!bag!technique!(Eno!1960;!Binkley!and!
Hart!1989).!!Conducting!the!N!transformation!assay!in!the!field!is!useful!because!possible!
treatment!effects,!such!as!temperature!differences,!can!be!included!in!the!incubation.!!
Three!pairs!of!soil!cores!(10!cm!depth,!246!cm3)!were!removed!from!each!plot!(6!cores!x!
10!treatment!plots!x!3!sites!=!180!cores).!!Soil!core!pairs!were!taken!from!a!random!
location!within!each!plot,!with!a!distance!of!5!cm!between!paired!soil!cores.!!One!core!from!
81!

each!pair!was!placed!in!a!polyethylene!bag!and!buried!at!the!same!depth!it!was!taken,!while!
the!other!soil!core!was!transported!on!ice!to!the!laboratory!for!initial!N!pool!size!
determination.!!Soil!cores!were!incubated!in!the!field!from!15!July!to!15!August!(30!days),!
after!which!they!were!transported!to!the!lab!for!final!N!pool!size!determination.!!From!the!
time!of!initial!in*situ*setup!to!the!end!of!the!incubation,!water!levels!were!above!the!soil!
surface!at!Glasby!and!LLP2,!while!at!LLP1!the!water!table!was!~!20!cm!below!the!soil.!!For!
processing,!soils!were!sieved!(4!mm),!subJsampled!for!determination!of!bulk!density,!
gravimetric!water!content!(GWC)!and!concentrations!of!NH4+!and!NO3J,!and!then!dried!to!a!
constant!mass!at!80°C.!!Dried!soils!were!ground!using!a!mortal!and!pestle!and!analyzed!on!
an!elemental!combustion!system!(Costech!ECS!4010,!Valencia,!CA)!for!%C!and!%N.!!
Concentrations!of!inorganic!N!for!both!initial!and!final!soil!cores!were!determined!on!
subsamples!of!all!soils!via!extraction!with!2!M!KCl!and!analyzed!by!the!microplate!method!
for!nitrate!and!ammonium!using!protocols!developed!by!Dr.!David!Rothstein!(Dept.!of!
Forestry,!MSU).!!Net!rates!of!N!mineralization!and!nitrification!were!calculated!from!the!
changes!in!inorganic!N!(NH4+!+!NO3J)!or!NO3JJN,!respectively,!during!the!incubation!period!
(initial!–!final!pool!sizes).!!!
!
Denitrification*assay!
A!laboratory!denitrification!assay!was!performed!to!determine!treatment!effects!on!
denitrification!potential.!!On!5!November!2011,!a!10!cm!soil!core!(246!cm3)!was!collected!
from!each!treatment!plot!at!each!site,!transported!to!the!lab!on!ice,!and!kept!at!4°C!until!
processed.!!At!the!time!of!soil!harvest,!water!levels!were!above!the!soil!surface!(~!30!cm)!at!

82!

Glasby,!at!the!soil!surface!at!LLP2,!and!below!the!soil!surface!at!LLP1.!!On!6!November!
2011,!soil!cores!were!sieved!(4mm)!and!then!two!subsamples!(25!ml)!were!kept!on!ice!and!
transported!to!Dr.!Jennifer!Tank’s!lab!at!the!University!of!Notre!Dame!where!the!assay!was!
performed!(10!treatment!plots!x!3!sites!x!2!replicate!subsamples!=!60!assay!samples).!!On!7!
November!2011,!denitrification!rates!were!determined!using!the!chloramphenicolJ
amended!acetylene!(C2H2)!inhibition!technique!(Groffman!et!al.!2006)!modified!by!the!
Tank!Lab.!!Briefly,!each!25!ml!subsample!was!added!to!a!125!ml!media!bottle!and!50!ml!
unfiltered!water!from!the!Glasby!site!was!added!and!mixed!with!the!soil!to!make!a!slurry.!!
The!media!bottle!was!sealed!with!an!nJbutyl!rubber!septum!in!the!lid!to!allow!gas!samples!
to!be!collected!with!a!5!ml!syringe.!!Chloramphenicol!was!added!to!the!slurry!to!inhibit!de*
novo!enzyme!production.!!Before!gas!samples!were!taken,!the!headspace!of!the!media!jars!
was!purged!with!helium!for!10!minutes!and!mechanically!agitated!to!achieve!anoxic!
conditions!throughout!the!slurry.!!Acetylene!gas!(15!ml)!was!then!added!to!the!media!
bottle!to!prevent!the!conversion!of!N2O!to!N2,!allowing!the!concentration!of!N2O!to!be!used!
for!denitrification!rate!determination.!!Five!5!ml!gas!samples!were!collected!starting!at!time!
0!and!then!hourly!for!4!hours!(total!of!5!samples!per!replicate).!!Samples!were!injected!into!
a!3!ml!scintillation!jar!and!then!analyzed!for!N2O!on!a!gas!chromatograph!with!an!electron!
capture!detector.!!Denitrification!rates!were!calculated!for!each!replicate!from!the!linear!
increase!in!N2O!concentration!over!the!course!of!the!4Jhour!incubation.!!Concentrations!
were!corrected!for!dilution!by!the!addition!of!N2!after!each!sample!was!collected!and!rates!
were!expressed!on!a!volumetric!and!gravimetric!basis.!!!
!
83!

Statistical*analyses!!!!!!
Site!differences!in!key!soil!characteristics!were!analyzed!by!general!linear!models!
(GLM)!to!help!explain!the!pattern!in!variation!among!sites!for!the!ecosystem!process!data!
collected!in!this!study.!Four!separate!multivariate!analysis!of!variance!(MANOVA)!tests!
were!performed!for!two!sets!of!response!variables:!1)!litter!bag!decomposition!rate,!
denitrification!rate,!net!N!mineralization!rate,!and!nitrification!rate!(hereafter!rate!
response!variables),!and!2)!soil!characteristics!collected!in!2010.!!For!each!set!of!response!
variables!the!effects!of!treatment!and!site!were!tested!individually!for!a!total!of!four!
MANOVA!tests.!!The!multivariate!analysis!was!used!to!protect!followJup!ANOVA!analysis!
from!inflated!alpha,!which!can!happen!when!multiple!ANOVA!tests!are!performed!
(Scheiner!2001).!!The!PillaiJBartlett!trace!(hereafter!Pillai)!was!used!as!the!test!statistic!for!
each!MANOVA.!!Separate!GLMs!(ANOVAs)!were!then!run!to!assess!which!factors!
significantly!influenced!individual!response!variables.!!!
For!the!analysis!of!light!levels,!soil!temperature,!soil!C!and!N!storage,!soil!NH4+!and!
NO3J!concentrations,!in*situ!net!N!mineralization/nitrification!rates,!potential!
denitrification!rates,!and!litter!bag!decomposition!rates,!GLMs!were!used!to!determine!
treatment!effects.!!For!these!analyses,!“site”!was!considered!a!random!factor!and!“plot”!was!
nested!within!“site”.!!Porewater!equilibrator!data!were!analyzed!differently!because!there!
was!no!replication!at!the!treatment!plot!level,!instead!there!was!only!one!equilibrator!per!
treatment!per!site,!and!therefore!plot!was!not!nested!within!site.!!Additionally,!depth!was!
included!as!a!fixed!factor!for!those!analyses!that!included!it.!!Tukey’s!HSD!multiple!
comparison!tests!were!performed!to!determine!significant!differences!among!factor!levels.!!!

84!

For!the!biogeochemical!rate!assays!(N!mineralization,!nitrification,!denitrification,!
and!decomposition),!both!simple!linear!regression!and!multiple!regression!analyses!were!
performed!to!determine!significant!controlling!soil!factors!on!rates.!!Many!of!the!
measurements!and!assays!described!above!were!additionally!analyzed!with!“site”!as!a!fixed!
effect!(without!“treatment”!as!a!fixed!effect)!because!of!the!strong!site!effects!that!were!
present,!which!can!be!linked!to!differences!in!hydrology.!!Model!diagnostics!were!assessed!
for!each!analysis!to!determine!if!the!residuals!were!normally!distributed!and!displayed!
constant!error!variances.!!Log!transformations!were!used!to!correct!for!any!
heteroscedasticity.!!All!variances!are!presented!as!standard!errors.!!All!statistical!tests!were!
performed!in!R!2.13.2!(R!Development!Core!Team!2011).!!!
!
(
(
(
(
(
(
(
(

85!

Table!3(1.!!Variation!among!sites!in!plant!characteristics,!soil!characteristics,!and!water!chemistry.!Variance!expressed!
as!standard!error.!AGB!=!aboveground!biomass,!DO!=!dissolved!oxygen,!SpC!=!specific!conductivity,!ORP!=!oxidation!
reduction!potential,!OM!=!organic!matter.!*!indicates!data!collected!in!2010.!
!!
Plant!Characteristics!(2009)!
!
!
!
!
!
Standing!litter! Ground!Litter! Total!Litter!!
Rhizome!!
Plant!Height!
AGB!!
AGB!per!tiller!
(g!m(2)!
(g!m(2)!
(g!m(2)!
(g!m(2)!
Site!
(cm)!
(g)!
(g)!
LLP1!
361!±9.4!
1742!±489!
47.8!±6.0!
580!±335!
1545!±1426! 2126!±1315! 584!±186!
LLP2!
383!±29.0!
1668!±422!
55.2!±8.3!
1157!±344!
1184!±397!
2341!±145!
813!±596!
Glasby!
391!±15.0!
1868!±263!
69.5!±10.6!
724!±291!
1225!±549!
1950!±548! 1422!±576!
!!
Soil!Characteristics!(2009)!
!
!
!
!
!
Bulk!density! Ammonium*!
Nitrate*!
OM!Depth!
(3)!
(1)!
(g!cm
(mg!N!kg
(mg!N!kg(1)!
Site!
Soil!%C!
Soil!%N!
Soil!C:N!
(cm)!
LLP1!
66.7!±10.2!
0.255!±0.030!
4.16!±1.55!
747.64!±329.77! 25.07!±1.76!
0.25!±0.03! 13.45!±0.48!
LLP2!
55.2!±6.2!
0.161!±0.033! 14.36!±4.78!
69.68!±97.42!
40.06!±1.96!
0.16!±0.03! 13.07!±0.68!
Glasby!
53.9!±9.2!
0.157!±0.460! 19.79!±7.66!
77.55!±84.72!
37.32!±5.36!
0.16!±0.05! 14.18!±0.34!
!!
Water!Chemistry!(2010)!
!
!
!
!
!
SpC!
DO!
Salinity!
ORP!
(1)!
(1)!
(µS!cm
(mg!L
Site!
%DO!
pH!
(ppt)!
(mV)!
!!
LLP1!
0.737!±0.75!
0.6!±0.16!
5.9!±1.5!
7.46!±0.19!
0.36!±0.04!
(179!±56!
!
LLP2!
0.744!±0.12!
0.64!±0.15!
6.5!±1.4!
6.71!±0.09!
0.36!±0.06!
(5!±11!
!
Glasby! 0.442!±0.10!
0.54!±0.14!
5.1!±1.2!
6.48!±0.08!
0.21!±0.04!
(18.2!±14!
!!
!!
Major!Ions!(ppm;!2009!and!2010)!
!
!
!
!
Cl(!
NO3(!
SO42(!
Ca2+!
Mg2+!
Na+!
K+ !
Site!
(ppm)!
(ppm)!
(ppm)!
(ppm)!
(ppm)!
(ppm)!
(ppm)!
LLP1!
30.69!±7.43!
0.017!±0.028! 6.64!±12.10!
86.73!±26.03!
18.08!±6.12! 16.51!±4.63! 2.86!±0.64!
LLP2!
72.54!±23.10! 0.005!±0.001!
1.00!±0.16!
90.46!±27.13!
23.12!±5.12! 27.17!±13.18! 0.52!±0.77!
Glasby! 56.88!±13.75! 0.005!±0.006!
0.48!±0.21!
67.90!±28.86!
16.51!±5.20! 36.29!±13.60! 0.36!±0.13!
!
!
86!

!
!
Table!3(1!(continued)!
!!
Roots!!
Total!BGB!
(g!m(2)!
(g!m(2)!
149!±112!
734!±278!
224!±94!
1038!±642!
1350!±445!
2773!±812!
!
!!
Soil!C!Stock!
Soil!N!Stock!
(2)!
(g!m
(g!m(2)!
6368!±523!
473!±38!
6425!±1136!
491!±84!
5678!±994!
401!±74!
!
!!
!!
!!
!
!!
!
!!
!!
!!
!
!!
!!
!!
!
!!
!
!!
!!
!!

!
!
!
!
!
!
!
!
!
!
!
!
!

!
!
!

87!

0

0.5

1 km

±
LLP
Site 2

[ [

LLP
Site 1

Lake
Lansing

Figure!3)1.!!Map!showing!the!location!of!the!two!monospecific!stands!of!Phragmites+
australis!at!Lake!Lansing!Park!(LLP1!and!LLP2),!Haslett,!MI.!!!
!
!
!
!
!
!
!
!
!
!
!
!
!
!

88!

!

Village of Delton

Upper
Crooked
Lake

Glasby
Lake
Site

[

±

0

0.5

1 km

Figure!3)2.!!Map!showing!the!location!of!the!monospecific!stand!of!Phragmites+australis!in!
the!wetland!area!surrounding!Glasby!Lake!(Glasby),!Delton,!MI.!
!
!
!
!
!
!
!
!
!
!
89!

!

Results!
Site+Characteristics!!!!!
For!soil!characteristics,!multivariate!analysis!showed!significant!effects!of!site!and!
depth!(Pillai!=!1.51,!approx.!F16,48!=!16.06,!p!<!0.001,!Pillai!=!0.57,!approx.!F8,41!=!6.84,!p!<!
0.001,!respectively).!!There!was!also!a!significant!site!x!depth!interaction!(Pillai!=!0.51,!
approx.!F16,84!=!1.80,!p!=!0.045).!!Protected!univariate!analysis!showed!there!were!
significant!site!effects!for!nitrate,!ammonium,!and!soil!C:N!ratio!(Table!3)2).!!LLP1!soil!had!
greater!nitrate!availability!and!lower!soil!moisture!and!ammonium!availability!than!either!
LLP2!or!Glasby,!while!Glasby!had!a!higher!soil!C:N!ratio!than!LLP1!and!LLP2.!!Soil!C!and!N!
stocks!and!soil!%!C!and!N!were!also!significantly!different!among!sites!(Table!3)2).!!There!
was!a!significant!site!x!depth!interaction!for!both!soil!%!C!(p!=!0.040)!and!%!N!(p!=!0.085):!!
LLP1!and!Glasby!had!greater!soil!%!C!and!N!at!0)5!cm!depth!compared!to!at!5)10!cm!depth,!
but!there!were!no!differences!between!depths!at!LLP2.!!Soil!C!and!N!stocks!followed!a!
similar!pattern!of!higher!stocks!at!5)10!cm!depth!compared!to!at!0)5!cm!depth!(significant!
depth!effect;!p!<!0.001!for!both!soil!C!and!N!stock),!along!with!LLP1!having!greater!stocks!
than!LLP2!and!Glasby!(significant!site!effect;!Table!3)2).!!!
Water!table!position!measured!in!2008)2010!(Figures!3)3!to!3)5)!by!pressure!
transducers!installed!at!each!site!are!informative!because!they!help!to!explain!the!variation!
among!sites!for!many!of!the!variables!discussed!above.!!There!are!a!number!of!points!to!be!
made!about!the!water!table!position!data:!!

90!

(1)!Glasby!had!a!higher!water!table!position!throughout!all!recorded!time!periods!
compared!to!LLP1,!while!LLP2!had!the!highest!water!table!position!throughout!
2009!and!the!second!highest!position!in!2010;!!
(2)!Wet!and!cool!spring!and!summer!conditions!in!2009!lead!to!higher!than!average!
water!levels!across!central!Michigan,!leading!to!high!water!table!position!at!
LLP1!and!LLP2;!
(3)!In!September!of!2008!and!2010,!there!was!a!dramatic!increase!in!water!table!
position!for!most!sites!following!heavy!rainfall;!!
(4)!In!2010,!when!most!of!the!data!analyzed!above!were!collected,!the!Glasby!water!
level!was!always!at!least!10!cm!above!the!soil!surface,!while!LLP1’s!water!level!
was!always!below!the!soil!surface.!!LLP2’s!water!level!was!closer!to!the!soil!
surface!and!shifted!from!above!to!below!the!soil!surface!multiple!times!over!
the!recorded!period!in!2010.!!!
A!summary!of!the!average!water!table!position!can!be!found!in!Figure!3)6.!!These!site!
differences!in!hydrology!likely!explain!the!variation!in!soil!moisture!differences!among!
sites:!!LLP2!had!the!greatest!soil!moisture,!followed!by!Glasby,!and!then!LLP1!(significant!
site!effect;!p!<!0.001).!
!

While!there!was!little!difference!in!total!aboveground!biomass!production!and!plant!

height!among!sites,!there!was!a!significant!site!effect!on!rhizome,!root,!and!total!
belowground!biomass!(BGB)!(total!BGB:!F2,12!=!8.35,!p!=!0.005).!!Glasby,!the!most!
consistently!saturated!site,!had!the!highest!BGB,!while!LLP2!and!LLP1,!which!had!either!
fluctuating!water!levels!or!water!levels!consistently!below!the!soil!surface,!had!significantly!
lower!BGB.!!
91!

!
Litter+and+AGB+effects+on+soil+and+porewater+chemistry,+light+levels,+and+temperature+!
For!soil!characteristics,!results!from!the!MANOVA!indicated!that!when!analyzed!for!
the!effects!of!treatment!and!depth,!treatment!was!not!significant!(Pillai!=!0.23,!approx.!
F16,84!=!0.69,!p!=!0.798)!but!depth!was!(Pillai!=!0.51,!approx.!F8,41!=!5.41,!p!<!0.001).!!
Protected!ANOVAs!indicated!bulk!density,!stocks!of!soil!C!and!N,!and!soil!C:N!ratio!were!all!
significantly!greater!at!5)10!cm!depth!compared!to!at!0)5!cm!depth!(Table!3)3).!!
Conversely,!ammonium,!nitrate,!and!soil!%!C!and!N!were!all!significantly!greater!at!0)5!
depth!compared!to!at!5)10!cm!depth!(Table!3)3).!!!
Photosynthetically!active!radiation!(PAR)!below!the!canopy!varied!across!
treatments!with!the!highest!values!recorded!in!the!total!removal!plots!(781!±!191!µmol!m)2!
sec)1),!nearly!18!fold!greater!than!in!the!reference!plots!(44!±!15!µmol!m)2!sec)1)!(Figure!3)
7;!significant!treatment!effect,!p!<!0.001).!!Levels!of!PAR!in!the!biomass!removal!and!litter!
removal!plots!were!intermediate,!and!did!not!statistically!differ!from!one!another.!
Averaged!across!sites,!soil!temperature!measurements!made!during!midday!visits!
ranged!from!17.1!±!0.54!oC!at!a!depth!of!40!cm!for!the!reference!treatment!to!24.77!±!2.67!
oC!at!the!soil!surface!for!the!total!removal!treatment!(Figure!3)8).!!In!all!treatments!besides!

total!removal,!there!was!a!gradual!decrease!in!temperature!from!ambient!to!40!cm!soil!
depth!(significant!depth!effect;!Table!3)4).!!For!the!biomass!removal!treatment,!there!was!a!
significant!decrease!in!temperature!from!ambient!air!to!the!soil!surface!followed!by!a!
decrease!from!a!soil!depth!of!2!cm!to!40!cm!similar!to!other!treatments!(significant!
treatment!x!depth!interaction;!Table!3)4).!!The!total!removal!treatment!showed!an!increase!

92!

in!temperature!from!ambient!to!soil!surface,!though!they!were!not!significantly!different.!!
Reference!plots!had!the!lowest!recorded!soil!temperature!for!each!soil!depth,!as!well!as!
ambient!temperature!(significant!treatment!effect;!Table!3)4).!!!
For!HOBO!datalogger!temperature!measurements!recorded!in!2010,!which!included!
all!four!treatment!plots,!there!was!an!interaction!between!depth!and!date:!temperature!
variation!among!days!was!greater!for!ambient!air!readings!compared!to!soil!readings!
(Figures!3)9!to!3)12;!significant!depth!x!date!interaction;!Table!3)5).!!From!12!July!to!the!
beginning!of!September,!total!removal!plots!had!the!highest!temperatures!followed!by!
litter!removal!plots,!biomass!removal!plots,!and!reference!plots.!Starting!at!the!beginning!of!
September!and!lasting!until!the!end!of!the!recording!period!(28!October),!the!rank!order!of!
decreasing!temperature!changed!to!reference,!biomass!removal,!total!removal,!and!finally!
litter!removal!(significant!treatment!x!date!interaction;!Table!3)5).!!The!significant!
treatment!effect!(p!=!0.003)!was!caused!by!total!removal!plots!having!higher!temperatures!
compared!the!other!treatment!levels,!from!the!start!of!the!recording!period!to!
approximately!the!beginning!of!September.!!
Analysis!of!porewater!equilibrator!wells!after!field!incubation!revealed!distinct!
changes!in!major!solute!chemistry!with!depth!below!the!water!table.!!There!was!a!
significant!treatment!effect!on!Na+!and!Cl)!concentrations,!as!the!biomass!removal!
treatment!plots!had!lower!concentrations!of!these!relatively!conservative!ions!compared!to!
the!reference!and!litter!removal!plots!(Figures!3)13!and!3)14;!significant!treatment!effect;!
Table!3)6).!!Concentrations!of!Mg2+!were!highest!in!the!litter!removal!plots!compared!to!
reference!and!biomass!removal!plots!(Figure!3)15;!significant!treatment!effect;!Table!3)6)!

93!

and!this!pattern!was!stronger!at!greater!depth,!though!the!interaction!was!not!significant.!!
Concentrations!of!Ca2+!were!highest!in!reference!plots!compared!to!biomass!and!litter!
removal!plots!(Figure!3)16;!significant!treatment!effect;!Table!3)6).!!Across!treatments,!
Mg2+!and!Ca2+!concentrations!increased!with!depth!(significant!depth!effect;!Table!3)6).!!
Sulfate!and!nitrate!decreased!with!well!depth!(Figure!3)17!and!3)18;!significant!depth!
effect;!p!<!0.001),!and!though!there!were!no!significant!effects!of!treatment!for!sulfate,!
nitrate!was!significantly!lower!in!reference!plots!than!litter!removal!plots!(significant!
treatment!effect;!p!=!0.049,!Table!3)6).!Total!dissolved!phosphate!(TDP)!and!potassium!did!
not!vary!with!depth!or!among!treatments.!!!!!!
!
Carbon+and+nitrogen+cycling!
For!the!carbon!and!nitrogen!cycling!rate!response!variables!(litter!bag!
decomposition!rate,!denitrification!rate,!net!N!mineralization!rate,!and!nitrification!rate),!
there!were!no!significant!effects!of!litter!and/or!biomass!removal!treatment!(MANOVA;!
Pillai!=!0.30,!approx.!F15,72!=!0.52,!p!=!0.919),!but!that!there!were!significant!site!effects!
(Pillai!=!1.29,!approx.!F10,48!=!8.74,!p!<!0.001).!!!
For!univariate!analysis,!there!were!no!significant!treatment!effects!on!in+situ!N!
mineralization!or!nitrification!rates,!though!there!were!strong!site!effects.!!Both!Glasby!and!
LLP2!had!positive!N!mineralization!rates!(3.99!and!4.96!mg!N!kg)1!soil,!respectively)!while!
negative!N!mineralization!(i.e.,!net!immobilization!and/or!denitrification!of!dissolved!
inorganic!N)!occurred!at!LLP1!()0.88!mg!N!kg)1!soil)!(Figure!3)19;!significant!site!effect,!

94!

F2,87!=!65.57;!p!<!0.001).!!Net!nitrification!rates!were!negative!for!LLP1!and!LLP2!()0.39!
and!)0.15!mg!N!kg!soil)1,!respectively)!and!zero!for!Glasby!(Figure!3)20;!significant!site!
effect,!F2,87!=!1.29;!p!<!0.001).!!Because!LLP1!and!LLP2!had!positive!soil!nitrate!
concentrations!at!the!beginning!of!the!incubation,!the!low!net!nitrification!rates!were!likely!
caused!by!denitrification!(nitrate!loss)!occurring!throughout!the!30)day!incubation.!!Soil!
moisture!and!soil!%!N!were!positively!related!to!net!N!mineralization!(Figure!3)21!and!3)
22;!adjusted!R2!=!0.297,!p!<!0.001,!adjusted!R2!=!0.406,!p!<!0.001,!respectively).!!
Ammonium!was!positively!related!to!soil!moisture!(Figure!3)23;!adjusted!R2!=!0.125,!p!<!
0.001),!while!nitrate!was!negatively!related!to!soil!moisture!(adjusted!R2!=!0.045,!p!<!
0.025),!though!the!relationship!was!weak.!!!!
!

There!were!no!treatment!effects!on!litter!bag!decomposition!rates,!though!there!

were!significant!depth!effects.!!Trends!in!decomposition!were!similar!for!both!Phragmites!
stems!and!filter!paper:!filter!paper!(Figure!3)24;!p!<!0.001;!Table!8)!and!stem!(Figure!3)25;!
p!=!0.015;!Table!3)7)!material!incubated!within!soil!had!a!lower!decomposition!rate!
compared!to!when!incubated!on!the!soil!surface,!though!there!were!no!differences!within!
total!removal!plots.!!When!litter!bag!assay!data!were!analyzed!to!determine!site!x!depth!
effects,!their!interaction!was!found!to!be!significant.!!For!stem!decomposition,!rates!at!both!
depths!at!LLP1!and!Glasby!were!not!different!from!one!another,!but!at!LLP2!stem!tissue!
decomposed!faster!on!the!soil!surface!and!slower!in!soil!compared!to!LLP1!and!Glasby!
(Figure!3)26;!significant!site!x!depth!interaction;!Table!3)7).!!For!filter!paper!
decomposition,!there!was!no!statistical!difference!among!sites!for!filter!paper!incubated!in!

95!

soil,!while!filter!paper!incubated!on!the!soil!surface!decomposed!faster.!!This!faster!
decomposition!on!the!soil!surface!was!not!observed!at!LLP1!(Figure!3)26;!significant!site!x!
depth!interaction;!Table!3)7).!!Overall,!filter!paper!(k!constant!=!0.0114!d)1)!decomposed!at!
a!faster!rate!than!Phragmites!stem!tissue!(k!constant!=!0.0022!d)1)!(p!<!0.001).!!
!

Similar!to!the!in+situ!N!mineralization/nitrification!incubation!and!litter!bag!assay,!

no!significant!treatment!effects!were!found!for!potential!denitrification!rates.!!There!were!
strong!site!effects,!and!expressing!denitrification!rates!on!a!volumetric!(cm)3)!or!
gravimetric!(g)1!soil!and!g)1!soil!C)!basis!yielded!similar!results:!both!LLP1!and!LLP2!had!
significantly!greater!N2O!production!rates!than!Glasby!(Figure!3)28;!p!<!0.001!for!all!cases;!
for!cm)3!F2,27!=!11.41),!which!had!almost!no!detectable!amount!of!N2O!production.!!
Because!mode!of!expression!did!not!affect!statistical!conclusions,!only!denitrification!rates!
expressed!on!a!volumetric!basis!(cm)3)!will!be!discussed!further.!!The!best!fit!multiple!
regression!model!(based!on!AIC!values!and!overall!model!significance)!showed!
denitrification!rates!were!positively!related!to!soil!nitrate!(Figure!3)29;!p!<!0.001)!and!
negatively!related!to!soil!C:N!ratio!(Figure!3)30;!p!<!0.001),!with!the!overall!model!
explaining!41%!of!the!variation!in!denitrification!rates.!!
!!!!!!!!!!!!!!!!
!
!
!
!
!

96!

!
Table!3(2.!Mixed!model!F(values!for!the!effect!of!Site!and!Depth!on!Bulk!Density,!Ammonium,!Nitrate,!Soil!%C,!Soil!%N,!
Soil!C:N!ratio,!and!Soil!C!and!N!Stock.!!df!indicates!degrees!of!freedom.!!Significance!is!denoted!with!asterisk(s).!
!
Source!
!
Site!
!
Depth!
!
T!x!D!
!!
*p!<!0.05!
**p!<!0.001!
!

!

!
df!
!
3!
!
1!
!
3!
!!
!
!

!
Bulk!Density!
!
29.56**!
!
32.99**!
!
4.13*!
!!
!
!

!
Ammonium!
!
23.10**!
!
8.21*!
!
1.39!
!!
!
!

!

!

!

Nitrate! Soil!%C!
!
!
18.44**! 53.50**!
!
!
6.07*!
7.12*!
!
!
0.51!
3.41*!
!!
!!
!
!
!
!

!
Soil!C:N!
!
23.25**!
!
17.11**!
!
3.72*!
!!
!
!

Soil!%N!
!
65.52**!
!
16.80**!
!
2.58*!
!!

!
!

!
Soil!C!Stock!
!
4.76*!
!
33.80**!
!
0.32!
!!
!
!

!
Soil!N!Stock!
!
7.88**!
!
19.79**!
!
0.27!
!!
!
!

Table!3(3.!Mixed!model!F(values!for!the!effect!of!Treatment!and!Depth!on!Bulk!Density,!Ammonium,!Nitrate,!Soil!%C,!
Soil!%N,!Soil!C:N!ratio,!and!Soil!C!and!N!Stock.!!df!indicates!degrees!of!freedom.!!Significance!is!denoted!with!asterisk(s).!
!
Source!
!
Treatment!
!
Depth!
!
T!x!D!
!!
!
*p!<!0.05!
**p!<!0.001!

!
df!
!
3!
!
1!
!
3!
!!
!
!
!

!
Bulk!Density!
!
0.22!
!
27.34**!
!
0.08!
!!
!
!
!

!
Ammonium!
!
1.23!
!
8.09*!
!
0.75!
!!
!
!
!

!

!
Nitrate! Soil!%C!
!
!
1.87!
0.55!
!
!
6.15*!
6.34*!
!
!
0.03!
0.10!
!!
!!
!
!
!
!
!
!

97!

!

!
Soil!%N!
!
0.34!
!
15.16**!
!
0.15!
!!

!
!
!

!
Soil!C:N!
!
0.65!
!
14.57**!
!
0.12!
!!

!
!
!

!
Soil!C!Stock! Soil!N!Stock!
!
!
0.89!
0.94!
!
!
33.08**!
19.46**!
!
!
0.26!
0.28!
!!
!!
!
!
!
!
!
!

Table!3(4.!Summary!of!two(factor!ANOVA!for!the!effect!of!Treatment!
and!Depth!on!soil!temperature.!den!df!indicates!the!denominator!
degrees!of!freedom!and!num!df!indicates!numerator!degrees!of!
freedom.!
!
!
!
!
!
Source!
num!df!
den!df!
F!
P(value!
!
!
!
!
!
Treatment!
3!
174!
9.33!
<0.0001!
!
!
!
!
!
Depth!
6!
174!
62.41!
<0.0001!
!
!
!
!
!
T!x!D!
18!
174!
2.07!
0.0087!
!!
!!
!!
!!
!!
!
!
Table!3(5.!Summary!of!Repeated!Measures!ANOVA!for!the!effect!of!Treatment,!
Depth,!and!Time!on!soil!temperature!during!the!2010!growing!season.!!den!df!
indicates!denominator!degrees!of!freedom!and!num!df!indicates!numerator!
degrees!of!freedom.!
!
!
!
!
!
Between&Subjects&
!
!
!
!
&
!
!
!
!
Source!
!num!df!
den!df!
F!
P(value!
!
!
!
!
!
Treatment!
3!
28!
5.82!
0.0032!
!
!
!
!
!
Depth!
3!
28!
3.83!
0.0203!
!
!
!
!
!
Treatment!x!Depth!
9!
28!
0.13!
0.9982!
!
!
!
!
!
Within&Subjects&
!
!
!
!
&
!
!
!
!
Source!
!num!df!
den!df!
F!
P(value!
!
!
!
!
!
Time!
108!
3181!
1518.51!
<0.0001!
!
!
!
!
!
Time!x!Treatment!
324!
3181!
2.46!
<0.0001!
!
!
!
!
!
Time!x!Depth!
324!
3181!
31.84!
<0.0001!
!
!
!
!
!
Time!x!Treat.!x!Depth!
972!
3181!
0.64!
1.0000!
&&
!!
!!
!!
!!
!
!
!
98!

!

!
!
!
!
!
!

Table!3(6.!Mixed!model!F(values!for!the!effect!of!Treatment!and!Depth!on!TDP!(total!dissolved!
phosphate),!Mg2+,!Ca2+,!Na+,!K+,!SO42(,!Cl(,!and!NO3(!concentrations!from!porewater!
equilibrators.!Significance!is!denoted!with!asterisk(s).!df!indicates!degrees!of!freedom.!
!
!
!
!
!
!
!
!
!
!
2+!
2+!
+!
+!
2(!
(!
Mg
Ca
Na
K
SO4
Cl
NO3(!
Source!
df! TDP!
!
!
!
!
!
!
!
!
!
!
Treatment!
2! 1.82!
3.29*! 7.54*! 4.93*! 2.03!
1.55! 17.34**! 3.16*!
!
!
!
!
!
!
!
!
!
!
Depth!
13! 1.30! 9.20**! 5.44**! 0.30!
0.39! 4.48**! 0.54!
2.91*!
!
!
!
!
!
!
!
!
!
!
Treatment!x!Depth! 26! 0.66!
0.99!
0.61! 0.78!
1.23!
0.21!
0.21!
0.51!
!!
!!
!!
!!
!!
!!
!!
!!
!!
!!
!
!
!
!
!
!
!
!
!
!
*p!<!0.05!
!
!
!
!
!
!
!
!
!
**p!<!0.001!
!
!
!
!
!
!
!
!
!

99!

!
Table!3(7.!Summary!of!two(factor!ANOVAs!for!the!effect!of!Treatment!
and!Depth!on!stem!and!filter!decomposition!and!Site!and!Depth!on!
stem!and!filter!decomposition!(expressed!as!first(order!rate!constants,!
k).!den!df!indicates!the!denominator!degrees!of!freedom!and!num!df!
indicates!numerator!degrees!of!freedom.!
!
!
!
!
!
Source!
num!df!
den!df!
F!
P(value!
!
!
!
!
!
Stem%k%constant%
!
!
!
%
!
!
!
!
Treatment!
3!
44!
0.60!
0.6178!
!
!
!
!
!
Depth!
1!
44!
6.43!
0.0148!
!
!
!
!
!
T!x!D!
3!
44!
1.06!
0.3745!
!
!
!
!
!
Filter%k%constant%
!
!
!
%
!
!
!
!
Treatment!
3!
44!
0.67!
0.5717!
!
!
!
!
!
Depth!
1!
44!
27.21!
<0.0001!
!
!
!
!
!
T!x!D!
3!
44!
1.62!
0.1976!
!
!
!
!
!
Stem%k%constant%
!
!
!
%
!
!
!
!
Site!
2!
54!
1.69!
0.1933!
!
!
!
!
!
Depth!
1!
54!
6.95!
0.0110!
!
!
!
!
!
S!x!D!
2!
54!
5.12!
0.0092!
!
!
!
!
!
Filter%k%constant%
!
!
!
%
!
!
!
!
Site!
2!
54!
21.50!
<0.0001!
!
!
!
!
!
Depth!
1!
54!
35.71!
<0.0001!
!
!
!
!
!
S!x!D!
2!
54!
10.33!
0.0002!
!!
!!
!!
!!
!!
!
!
!
!

100!

50$

Glasby$
LLP1$

40$
30$
Water&Level&(cm)&

20$
10$
0$
!10$
!20$
!30$
!40$
!50$
7/18/08$

8/2/08$

8/17/08$

9/1/08$

9/16/08$

10/1/08$

Date&
Figure!3(3.!!Water!table!position!at!Glasby!and!LLP1!from!July!to!October!of!2008.!!Zero!
water!level!represents!the!soil!surface!with!positive!water!levels!indicating!flooding!
(standing!water)!and!negative!values!indicating!a!water!table!below!the!soil!surface.!
!
!

101!

!

50$
40$
30$
Water&Level&(cm)&

20$
10$
0$
!10$
!20$

Glasby$

!30$

LLP2$
LLP1$

!40$
!50$
8/7/09$

8/22/09$

9/6/09$

9/21/09$

10/6/09$ 10/21/09$ 11/5/09$

Date&

Figure!3(4.!!Water!table!position!at!Glasby,!LLP1,!and!LLP2!from!August!to!November!of!
2009.!!Zero!water!level!represents!the!soil!surface!with!positive!water!levels!indicating!
flooding!(standing!water)!and!negative!values!indicating!a!water!table!below!the!soil!
surface.!

102!

!

50$
40$
30$

Water&Level&(cm)&

20$
10$
0$
!10$
!20$
!30$
!40$
!50$

Glasby$
LLP1$
LLP2$

!60$
!70$
!80$
7/3/10$

7/23/10$

8/12/10$

9/1/10$

9/21/10$

10/11/10$

10/31/10$

Date&
!
Figure!3(5.!!Water!table!position!at!Glasby,!LLP1,!and!LLP2!from!July!to!October!of!2010.!!
Zero!water!level!represents!the!soil!surface!with!positive!water!levels!indicating!flooding!
(standing!water)!and!negative!values!indicating!a!water!table!below!the!soil!surface.!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!

103!

!
!
!
!
!
!
!
!
!
40$

Water&Level&(cm)&

20$
0$
!20$

2008$
2009$

!40$

2010$
!60$
Glasby$

LLP1$

LLP2$

Site&
!
Figure!3(6.!!Water!table!position!at!Glasby,!LLP1,!and!LLP2!for!2008!to!2010!(see!methods!
for!exact!time!periods).!!Zero!water!level!represents!the!soil!surface!with!positive!water!
levels!indicating!flooding!(standing!water)!and!negative!values!indicating!a!water!table!
below!the!soil!surface.!!Error!bars!represent!1!standard!deviation.!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!

104!

!
!
!
!
!
!
!
!
c

1000"
900"
PAR$(umol$m*2$s*1)$

800"
700"
600"
500"
400"
300"
200"
100"

b
a

b

0"
C"

BR"

LR"
Treatment$

TR"

!
Figure!3(7.!!Mean!light!levels!(PAR)!measured!directly!above!the!soil!surface!within!control!
(C),!biomass!removal!(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots!
averaged!across!sites.!!There!was!a!significant!treatment!effect!(F3,81!=!109.95,!p!<!0.001).!!
Same!letter!superscript!denotes!nonsignificant!differences!according!to!Tukey!post!hoc!
tests.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!
!

105!

!
!
30"

25"

Temperature)(C))

Ambient"
Soil"Surface"

20"

2cm"
10cm"

15"

20cm"
30cm"

10"

40cm"

5"

0"
C"

!
!

BR"

LR"
TR"
Treatment)
!
Figure!3)8.!!Mean!manual!temperature!measurements!taken!at!6!soil!depths!(and!ambient)!within!control!(C),!
biomass!removal!(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots!averaged!across!sites.!!There!
was!a!significant!interaction!between!treatment!and!depth!(F18,174!=!2.07,!p!<!0.009).!!Error!bars!represent!1!
SE.!

106!

30"

BR"
C"
LR"
TR"

Temperature)(C))

25"

20"

15"

10"

5"

0"
7/3/10"

7/23/10"

8/12/10"

9/1/10"
Date)

!
!

9/21/10"

10/11/10"

10/31/10"

!
Figure!3)9.!!Daily!ambient!mean!temperature!from!July!to!October!2010!within!control!(C),!biomass!removal!(BR),!litter!
removal!(LR),!and!total!removal!(TR)!treatment!plots.!

107!

30"

BR"
C"
LR"
TR"

Temperature)(C))

25"

20"

15"

10"

5"

0"
7/3/10"

!

7/23/10"

8/12/10"

9/1/10"

9/21/10"

10/11/10"

10/31/10"

Date)
!
Figure!3)10.!Daily!soil!surface!mean!temperature!from!July!to!October!2010!within!control!(C),!biomass!removal!(BR),!
litter!removal!(LR),!and!total!removal!(TR)!treatment!plots.!

108!

30"
BR"
C"
LR"
TR"

25"

Temperature)(C))

20"

15"

10"

5"

0"
7/3/10"

7/23/10"

8/12/10"

9/1/10"
Date)

!
!

9/21/10"

10/11/10"

10/31/10"

!
Figure!3)11.!Daily!mean!temperature!at!2!cm!soil!depth!from!July!to!October!2010!within!control!(C),!biomass!removal!
(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots.!

109!

30"
BR"
C"
LR"
TR"

25"

Temperature)(C))

20"

15"

10"

5"

0"
7/3/10"

7/23/10"

8/12/10"

9/1/10"
Date)

9/21/10"

10/11/10"

10/31/10"

!
Figure!3)12!Daily!mean!temperature!at!10!cm!soil!depth!from!July!to!October!2010!within!control!(C),!biomass!removal!
(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots.!

110!

!
!
!
!
!
!
!
!
!
!
0"

20"

40"

60"

Cl$(ppm)$
80"

100"

120"

140"

160"

0"
5"

Well$Depth$(cm)$

10"
15"
20"
25"
30"
35"
C"

40"

BR"

45"

LR"

50"

!

Figure!3)13.!!Mean!Cl)!concentrations!from!porewater!equilibrators!within!control!(C),!

biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!treatment!(F2,63!=!17.34,!p!<!0.001)!on!Cl)!concentrations,!
but!not!depth!or!their!interaction.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!
!
111!

!
!
!
!
!
!
!
!
!
!
0"

10"

20"

30"

Na$(ppm)$
40"

50"

60"

70"

80"

0"
5"

Well$Depth$(cm)$

10"
15"
20"
25"
30"
35"

C"

40"

BR"

45"

LR"

50"

!

Figure!3)14.!!Mean!Na+!concentrations!from!porewater!equilibrators!within!control!(C),!
biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!treatment!(F2,63!=!4.93,!p!=!0.01)!on!Na+!concentrations,!
but!not!depth!or!their!interaction.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!
!
112!

!
!
!
!
!
!
!
!
!
!
0"

10"

20"

Mg$(ppm)$
30"

40"

50"

60"

0"
5"

C"

Well$Depth$(cm)$

10"

BR"

15"

LR"

20"
25"
30"
35"
40"
45"

50"
!
2+!concentrations!from!porewater!equilibrators!within!control!(C),!
Figure!3)15.!!Mean!Mg
biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!treatment!(F2,63!=!3.29,!p!=!0.043)!and!depth!(F13,63!=!

9.20,!p!<!0.001)!on!Mg2+!concentrations,!but!not!their!interaction.!!Error!bars!represent!1!
SE.!!
!
!
!
!
!
!
!
!
!
!
!
113!

!
!
!
!
!
!
!
!
!
!
0"

50"

100"

Ca$(ppm)$

150"

200"

250"

0"
5"

Well$Depth$(cm)$

10"
15"
20"
25"
30"
35"
40"
45"

C"
BR"
LR"

50"

!

Figure!3)16.!!Mean!Ca2+!concentrations!from!porewater!equilibrators!within!control!(C),!
biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!treatment!(F2,63!=!7.54,!p!=!0.001)!and!depth!(F13,63!=!
5.44,!p!<!0.001)!on!Ca2+!concentrations,!but!not!their!interaction.!!Error!bars!represent!1!
SE.!!
!
!
!
!
!
!
!
!
!
!
!
114!

!
!
!
!
!
!
!
!
!
!
0"

5"

10"

15"

Sulfate$(ppm)$
20"
25"

30"

35"

40"

0"
5"

Well$Depth$(cm)$

10"
15"
20"
25"
30"
35"

C"

40"

BR"

45"

LR"

50"

!

Figure!3)17.!!Mean!SO42)!concentrations!from!porewater!equilibrators!within!control!(C),!
biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!depth!(F13,63!=!4.48,!p!<!0.001)!on!SO42)!concentrations,!
but!not!treatment!or!their!interaction.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!
!
115!

!
!
!
!
!
!
!
!
!
!
0"

0.2"

0.4"

Nitrate$(ppm)$
0.6"
0.8"

1"

1.2"

1.4"

0"
5"

Well$Depth$(cm)$

10"
15"
20"
25"
30"

C"

35"

BR"

40"

LR"

45"
50"

!

Figure!3)18.!!Mean!NO3))N!concentrations!from!porewater!equilibrators!within!control!(C),!
biomass!removal!(BR),!and!litter!removal!(LR)!treatment!plots!averaged!across!sites.!!
There!was!a!significant!effect!of!depth!(F13,63!=!3.16,!p!=!0.049)!and!treatment!on!NO3)!
(F13,63!=!2.91,!p!=!0.002)!concentrations,!but!not!their!interaction.!!Error!bars!represent!1!
SE.!!
!

116!

N"Mineraliza+on"(mg"N"kg11"soil)"

7#
6#
5#
4#
3#
2#
1#
0#
!1#
!2#

a
a

b

Glasby#

LLP1#

LLP2#

Nitrifica(on+(mg+N+kg01+soil)+

Site"
!
Figure!3)19.!!Mean!net!N!mineralization!rates!among!soil!collected!within!monospecific!
stands!of!Phragmites+australis!at!Glasby,!LLP1,!and!LLP2.!!The!effect!of!site!was!significant!
(F2,87!=!65.57;!p!<!0.001).!!Same!letter!superscript!denotes!nonsignificant!differences!
according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!
!
!
0.2#
0#
!0.2#
!0.4#
!0.6#
!0.8#
!1#
Glasby#

LLP1#

LLP2#

Site+
!
Figure!3)20.!!Mean!net!nitrification!rates!among!soil!collected!within!monospecific!stands!
of!Phragmites+australis!at!Glasby,!LLP1,!and!LLP2.!!The!effect!of!site!was!significant!(F2,87!=!
1.29;!p!<!0.001).!!Error!bars!represent!1!SE.!!!
!
!

117!

N$Mineraliza9on$(mg$N$kg<1$soil)$

14"
12"
10"
8"
6"
4"
2"
0"
02"
04"
06"
0.6"

0.65"

0.7"

0.75"

0.8"

0.85"

0.9"

0.95"

Soil$%$Moisture$

!
Figure!3)21.!!Regression!between!soil!%!moisture!and!net!N!mineralization!rates!(adjusted!
R2!=!0.297,!p!<!0.001).!
!
!
N$Mineraliza9on$(mg$N$kg<1$soil)$

14"
12"
10"
8"
6"
4"
2"
0"
02"
04"
06"
1"

1.5"

2"

2.5"

3"

3.5"

Soil$%$N$

!
Figure!3)22.!!Regression!between!soil!%!moisture!and!net!N!mineralization!rates!(adjusted!
R2!=!0.406,!p!<!0.001).!
!

118!

Ammonium$(mg$kg<1)$

140"
120"
100"
80"
60"
40"
20"
0"
0.6"

0.65"

0.7"

0.75"

0.8"

0.85"

0.9"

0.95"

Soil$%$Moisture$

Stem%Decomposi,on%Rate%(d21)%

!
Figure!3)23.!!Regression!between!soil!%!moisture!and!net!N!mineralization!rates!(adjusted!
R2!=!0.125,!p!<!0.001).!
!
!
0.0035#
0.0030#
0.0025#

a

a

a

a

ab

b

b

li/er#
soil#

ab

0.0020#
0.0015#
0.0010#
0.0005#
0.0000#
BR#

C#

LR#

Treatment%

TR#

!

Figure!3)24.!!Mean!first!order!rate!constants!(k;!day)1)!for!stems!incubated!within!control!
(C),!biomass!removal!(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots!over!
a!90!day!time!period!averaged!across!sites.!!There!was!a!significant!effect!of!depth!(F1,44!=!
6.43;!p!=!0.014),!but!not!treatment!or!their!interaction.!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!!!!
!

119!

Filter'Decomposi.on'Rate'(d41)'

0.025#

li.er#

a
0.020#

a

soil#

a

ab

0.015#

ab
b

0.010#

b

b

0.005#
0.000#
BR#

C#

LR#

TR#

Treatment'

!

Figure!3)25.!!Mean!first!order!rate!constants!(k;!day)1)!for!filters!incubated!within!control!

Stem%Decomposi,on%Rate%(d21)%

(C),!biomass!removal!(BR),!litter!removal!(LR),!and!total!removal!(TR)!treatment!plots!over!
a!90!day!time!period!averaged!across!sites.!!There!was!a!significant!effect!of!depth!(F1,44!=!
6.43;!p!<!0.001),!but!not!treatment!or!their!interaction.!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!!!!
!
!
0.0035#
0.0030#
0.0025#

li-er#

c
a

soil#

ab
b

b
e

0.0020#
0.0015#
0.0010#
0.0005#
0.0000#
GL#

LLP1#

LLP2#

Site%

!

Figure!3)26.!!Mean!first!order!rate!constants!(k;!day)1)!for!stems!incubated!at!Glasby!(GL),!
LLP1,!and!LLP2!sites!over!a!90!day!time!period.!!There!was!a!significant!interaction!
between!site!and!depth!(F2,54!=!5.12;!p!=!0.009).!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!!!!
!

120!

Filter'Decomposi.on'Rate'(d41)'

0.025#

li,er#

a

a

0.020#
0.015#

soil#

b

0.010#

c

c

c

LLP1#

LLP2#

0.005#
0.000#
GL#

Site'

!

Figure!3)27.!Mean!first!order!rate!constants!(k;!day)1)!for!filters!incubated!at!Glasby!(GL),!
LLP1,!and!LLP2!sites!over!a!90!day!time!period.!!There!was!a!significant!interaction!
between!site!and!depth!(F2,54!=!10.33;!p!<!0.001).!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!!!!!!!
!
!

N2O$(µmol$cm+3$day+1)$$

0.07%

a

a

LLP1%

LLP2%

0.06%
0.05%
0.04%
0.03%
0.02%
0.01%
0%
!0.01%

a
Glasby%

Site$

!
Figure!3)28.!!Mean!denitrification!rates!(N2O!production)!among!soil!collected!within!
monospecific!stands!of!Phragmites+australis!at!Glasby,!LLP1,!and!LLP2.!!The!effect!of!site!
was!significant!(F2,27!=!11.41;!p!<!0.001).!!Same!letter!superscript!denotes!nonsignificant!
differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!
!

121!

N2O$(µmol$cm<3$day<1)$$

0.16"
0.14"
0.12"
0.1"
0.08"
0.06"
0.04"
0.02"
0"
0"

200"

400"

600"

800"

1000"

1200"

Nitrate$(mg$kg<1)$

!
Figure!3)29.!!Regression!between!nitrate!and!denitrification!rates!(N2O!
production)(adjusted!R2!=!0.310,!p!<!0.001).!
!
0.2"

N2O$(µmol$cm<3$day<1)$$

0.15"
0.1"

0.05"
0"
12"

12.5"

13"

00.05"

13.5"

14"

14.5"

15"

15.5"

Soil$C:N$Ra9o$

!
!
Figure!3)30.!!Regression!between!soil!C:N!ratio!and!denitrification!rates!(N2O!production)!
(adjusted!R2!=!0.252,!p!<!0.001).!
!
!
!
!

122!

Discussion(
Water!table!position!varied!among!study!sites!seasonally!and!among!years,!and!
when!above!the!soil!surface,!the!depth!of!standing!water!varied!as!well.!!These!hydrologic!
differences!created!a!gradient!in!water!table!position!among!sites,!especially!in!2010,!that!
likely!influenced!several!of!the!results!discussed!above.!!The!more!pronounced!gradient!in!
2010!is!notable!because!that!was!the!year!most!of!the!investigations!occurred,!including!all!
of!the!process!rate!assays.!!Throughout!the!study!period!in!2010,!the!water!table!was!above!
the!soil!surface!(standing!water)!at!Glasby,!fluctuated!above!and!below!the!soil!surface!at!
LLP2,!and!was!below!the!soil!surface!at!LLP1!(Figure!3)5).!!Differences!in!water!table!
position!likely!influenced!site!soil!moisture,!availability!of!nutrients!due!to!changes!in!
redox!potential!caused!by!drying!and!rewetting,!and,!if!the!differences!in!hydrology!
occurred!on!a!long!enough!time!scale,!site!organic!matter!buildup.!!Data!support!these!
predictions;!LLP1!(lowest!water!table)!had!the!lowest!soil!%!moisture,!the!lowest!
ammonium!concentrations,!the!highest!nitrate!concentrations,!and!the!lowest!soil!%!C!(an!
estimate!of!organic!matter)!(Table!3)1).!!Ju!et!al.!(2006)!modeled!hydrologic!effects!on!C!
cycling!in!forests!and!wetlands!in!Canada!and!found!that!drainage!class!greatly!influenced!a!
wetlands!ability!to!accumulate!C,!with!poorly!drained!wetlands!accumulating!the!most!and!
well)drained!wetlands!accumulating!the!least.!!This!supports!my!findings!that!LLP1!(well)
drained)!had!the!lowest!soil!%C!and!Glasby!(pooly!drained)!the!highest.!!The!remainder!of!
this!section!will!focus!on!treatment!and!site!effects!on!the!ecosystem!parameters!measured!
in!this!study,!with!hydrology!as!the!main!mechanism!for!variation!among!sites.!
The!treatment!effects!on!both!light!levels!and!temperatures!during!the!growing!
season!followed!my!predictions:!control!plots!had!the!lowest!light!levels!and!the!lowest!

123!

temperatures!(for!manual!measurements),!total!removal!plots!had!the!highest!light!levels!
and!temperatures,!and!both!biomass!removal!and!litter!removal!plots!had!intermediate!
levels.!!These!data!suggest!a!number!of!effects!of!biomass!and!litter!removal.!!First,!light!
levels!were!dramatically!reduced!(18!fold!difference)!in!Phragmites!stands!compared!to!
when!Phragmites!was!absent!(Figure!3)7).!!Second,!litter!and!biomass!removal!both!
increased!light!levels!to!the!same!degree,!which!was!significantly!less!of!an!increase!
compared!to!when!it!was!completely!removed.!!This!also!supports!my!predictions!that!both!
litter!and!biomass!removal!treatments!would!increase!light!levels,!but!the!remaining!litter!
(biomass!removal)!or!biomass!(litter!removal)!would!reduce!light!levels!compared!to!when!
completely!removed!(total!removal).!!Similarly,!Farrer!and!Goldberg!(2009)!found,!in!a!
litter!transplant!experiment,!that!Typha! × glauca!litter!significantly!reduces!soil!surface!
light!levels,!but,!interestingly,!live!T.! × glauca!did!not!greatly!affect!light!levels.!!One!

€
explanation!for!this!difference!between!the!effects!of!live!biomass!of!Phragmites!and!T.! ×
€
glauca!on!light!levels!is!that!Phragmites!stems!have!a!branching!structure!to!them,!while!T.!
€
× glauca!has!a!much!more!linear!structure.!!Third,!even!though!there!were!differences!in!
light!levels!and!temperatures!among!treatment!plots,!the!differences!in!light!level!among!

€

plots!were!of!a!much!greater!magnitude!than!differences!in!temperature.!!One!possible!
reason!for!this!magnitude!discrepancy!is!that!light!level!determination!requires!the!
ceptometer!user!to!record!light!levels!around!noon!on!a!cloudless!sky.!!These!conditions!
produce!the!most!extreme!difference!in!light!levels!among!treatments!but!are!likely!not!to!
be!the!most!common!circumstance!each!site!experienced.!!Conversely,!while!manual!
temperature!measurements!were!taken!within!a!similar!time!range!as!light!levels!(11:00!
am!to!3:00!pm)!on!rainless!days,!cloudless!skies!were!not!requisite!of!temperature!data!

124!

collection.!!These!differences!likely!mean!that!manual!temperature!measurements!likely!
were!closer!to!actual!soil!conditions.!!Another!possibility!is!the!low!temperature!of!the!
surrounding!Phragmites!stands!reduced!the!temperature!within!the!2!x!2!m!plots.!!!
The!tall!stature!and!ability!of!living!biomass!and!litter!of!Phragmites+to!shade!the!
soil!surface!likely!facilitates!its!invasion!into!native!communities!by!creating!light!
limitation!below!its!canopy.!!Because!Phragmites!is!a!clonal!species,!and,!therefore,!new!
ramets!can!receive!resources!from!parent!plants,!its!own!success!will!not!be!greatly!
affected!by!the!low!light!conditions.!!One!consequence!for!wetland!restoration!of!the!
significant!treatment!effects!on!light!levels!and!temperature!is!it!is!common!practice!to!
manage!monospecific!stands!of!Phragmites!by!the!use!of!glyphosate,!which!usually!
successfully!kills!off!the!majority!of!individuals.!!If!this!sudden!die)off!isn’t!followed!by!a!
removal!of!all!of!the!standing!litter,!light!levels!might!still!be!low!enough!to!impede!the!
colonization!of!more!desirable!wetland!plants!until!standing!dead!biomass!decomposes,!
which!can!take!several!years.!!Farrer!and!Goldberg!(2009)!also!found!that!shading!effects!
from!T.! × glauca!litter!decreased!the!abundance!and!diversity!of!native!species.!!Gordon!
(1998)!found!that!the!ability!to!shade!native!competitors!was!a!commonality!among!

€invasive!species!in!Florida.!
!

The!temperature!dataloggers!allowed!me!to!capture!seasonal!variation!in!

temperature.!!Data!from!the!HOBO!dataloggers!showed!that!the!largest!temperature!
difference!among!treatments!was!at!the!soil!surface!where!total!removal!and!litter!removal!
plots!had!the!largest!temperature!difference!compared!to!reference!plots!(Figure!3)10).!!
This!temperature!difference!among!treatments!changed!at!the!beginning!of!September!to!
litter!and!total!removal!plots!having!the!lowest!temperatures,!though!before!the!beginning!

125!

of!September!total!and!litter!removal!plots!periodically!had!the!lowest!soil!surface!on!
relatively!cool!days!(less!than!~!19°C).!!!!This!change!that!started!in!September!was!not!
predicted!and!could!be!due!a!lower!capacity!for!total!and!litter!removal!plots!to!hold!heat!
close!to!the!soil!surface!during!periods!of!cooling!weather!and,!thus,!were!more!dependent!
on!incoming!solar!radiation!to!maintain!high!soil!surface!temperatures.!!MacKinney!(1929)!
found!similar!effects!of!forest!litter!on!temperature!fluctuations!over!multiple!seasons;!
litter!acted!like!an!insulator!by!decreasing!daily!high!temperatures!and!increasing!daily!
lows,!and!this!effect!diminished!with!soil!depth.!!Soil!temperatures!at!2!and!10!cm!depths!
showed!that!total!removal!plots!were!the!only!manipulated!plots!that!had!temperatures!
different!from!reference!plots,!though!this!difference!was!much!reduced!after!September!
(Figures!3)10!and!3)11).!!These!data!suggest!that!litter!plays!a!substantial!role!in!the!
temperature!regulation!of!the!soil!and!these!effects!are!likely!to!be!greater!with!high!litter!
producing!species!such!as!Phragmites.!
!

The!significant!treatment!effects!on!porewater!chemistry!likely!are!from!the!direct!

effect!of!Phragmites.!!Concentrations!of!Na+!and!Cl)!were!lower!in!the!biomass!removal!
plots!compared!to!the!reference!plots,!which!could!be!indicative!of!reduced!evaporative!
concentration!by!evapotranspiration.!!A!similar!pattern!of!increased!salinity!due!to!plant!
transpiration!was!found!in!mangrove!populations!in!French!Guiana!(Marchand!et!al.!2004),!
and!Spartina+alterniflora!is!known!to!alter!the!concentration!of!Na+,!Cl),!and!other!salts!due!
to!ion!exclusion!and!secretion!when!growing!in!brackish!waters!(Bradley!and!Morris!
1991).!!The!same!mechanism!could!also!cause!the!lower!concentrations!of!Ca2+!in!the!
biomass!removal!plots,!though!why!there!were!also!decreased!Ca2+!concentrations!in!the!

126!

litter!removal!plots!is!less!apparent.!!Similarly,!the!significant,!albeit!weak,!pattern!of!lower!
nitrate!concentrations!in!the!reference!plots!could!be!explained!by!direct!plant!uptake,!
though!nitrate!concentrations!were!not!lower!in!the!litter!removal!plot!where!live!biomass!
remained.!!Findlay!et!al.!(2003)!showed!that!nitrate!in!porewater!wasn’t!affected!by!the!
presence!of!living!Phragmites,!though!ammonium!did!increase!with!the!removal!of!
Phragmites.!
!

The!lack!of!any!treatment!effects!on!litter!bag!decomposition,!N!mineralization,!

nitrification,!and!denitrification!was!surprising,!especially!because!there!were!significant!
treatment!effects!on!light!levels!and!soil!temperatures.!!With!an!increase!in!light!levels,!and!
subsequent!soil!temperatures,!in+situ!litter!bag!decomposition!and!net!N!mineralization!
rates!should!have!increased!due!to!the!temperature!sensitivity!of!these!ecosystem!
processes.!!For!in+situ!N!mineralization/nitrification!rates,!one!possible!cause!for!the!lack!of!
treatment!effects!could!have!been!that!the!soil!cores!were!10!cm!in!depth!and!treatment!
effects!on!soil!temperature!were!greater!closer!to!the!soil!surface,!so!using!a!10!cm!core!
could!have!obscured!any!treatment!effect!present!near!the!soil!surface.!!For!the!litter!bag!
assay,!the!majority!of!the!time!(~!60!of!the!total!90!days)!the!litter!bags!were!in!the!field!
total!and!litter!removal!plots!had!lower!temperatures!than!reference!plots,!which!was!
opposite!of!what!was!predicted!and!likely!led!to!the!lack!of!treatment!effects!on!
decomposition!rates.!!Potential!denitrification!was!conducted!in!the!laboratory!free!from!
temperature!variation!experienced!in!the!field,!so!differences!in!denitrification!potential!
would!have!been!indicative!of!either!organic!matter!quality!changes!or!nitrate!availability,!
though!no!treatment!effects!were!detected.!!Contrary!to!what!I!found,!Findlay!et!al.!(2003)!
found!that!one!year!after!Phragmites!removal!by!herbicide,!potential!denitrification!

127!

dropped!by!50%!(compared!to!living!plots)!and!this!decrease!was!possibly!due!to!the!
cessation!of!oxygen!release!by!the!roots!which!allowed!for!nitrification!and!therefore!
nitrate!needed!for!denitrification.!!The!buildup!of!ammonium!after!Phragmites!removal!
gave!further!evidence!for!this!mechanism!(Findlay!et!al.!2003).!!
!

While!no!significant!treatment!effects!were!detected!for!any!ecosystem!process!rate!

investigated,!there!were!significant!site!effects.!!Net!N!mineralization!rates!were!the!lowest!
at!LLP1!where!rates!were!negative!(indicative!of!net!N!immobilization!and/or!
denitrification),!while!rates!at!Glasby!and!LLP2!were!positive!(Figure!3)19).!!The!biggest!
difference!between!LLP1!and!the!other!two!sites!was!the!low!position!of!the!water!table!
causing!drier!conditions.!!Likely!due!to!the!more!aerobic!soil!conditions,!nitrate!levels!were!
higher!at!LLP1!than!the!other!two!sites,!and!ammonium!concentrations!were!low!(Table!3)
1).!!The!negative!net!N!mineralization!and!nitrification!rates!therefore!could!have!been!a!
consequence!of!denitrification!occurring!within!the!sealed!soil!cores!in!the!field,!because!
while!LLP1!was!the!driest!site,!it!was!likely!still!moist!enough!to!have!anaerobic!soil!
microsites,!which!have!been!shown!to!be!sites!of!denitrification!(Burgin!et!al.!2011).!!
Because!LLP1!had!the!greatest!starting!nitrate!concentrations!and!ended!with!the!lowest,!
nitrification!followed!by!denitrification!is!a!likely!fate!of!remineralized!N.!!While!microbial!
N!immobilization!is!another!possibility!for!the!negative!net!rates!at!LLP1,!it!is!unlikely!
based!on!the!results!from!Chapters!2!and!4!that!showed!when!incubated!in!the!lab,!soil!
incubated!alone!rarely!shows!signs!of!N!immobilization.!!The!positive!relationship!between!
soil!%N!and!net!N!mineralization!rates!indicates!that!soils!with!more!N!(likely!in!organic!
forms)!have!a!greater!potential!for!mineralization!(Figure!3)22)!and!has!been!seen!in!
similar+in+situ!N!mineralization!assays!(Finzi!et!al.!1998).!

128!

!

There!were!no!depth!effects!on!stem!decomposition!at!Glasby!or!LLP1!and!rates!

were!comparable!between!sites.!!At!LLP2!there!were!strong!depth!effects!with!stem!
decomposition!being!the!greatest!at!the!soil!surface!(Figure!3)26).!!One!possible!
explanation!for!this!pattern!is!LLP1!and!Glasby!were!relatively!constant!in!water!table!
position!over!the!course!of!the!incubation,!though!the!actual!water!table!position!varied!
considerably!between!sites;!the!water!table!at!LLP1!was!below!the!soil!surface!and!Glasby!
had!constant!flooded!conditions.!!Conversely,!LLP2’s!water!table!fluctuated!from!above!to!
below!the!soil!surface!multiple!times!throughout!the!assay!periods,!which!could!have!
created!ideal!conditions!for!decomposition!as!the!wetting,!drying,!and!rewetting!likely!
added!moisture,!nutrients,!and!aerobic!conditions.!!Jarvis!et!al.!(2007)!showed!that!drying!
and!wetting!conditions!increased!decomposition!of!Mediterranean!soils,!but!there!is!also!
evidence!that!in!some!cases!a!wetting)drying!cycle!doesn’t!have!much!effect!(Day!1983)!
and!the!magnitude!of!effect!may!be!greater!for!arid!and!semiarid!soils!(Borken!and!Matzner!
2009).!!Filter!paper!decomposition!was!higher!on!the!soil!surface!at!Glasby!and!LLP2!
compared!to!LLP1!(Figure!3)27),!which!could!be!due!to!those!two!sites!having!periods!of!
complete!inundation!that!drove!the!breakdown!of!the!filter!paper!by!both!physical!and!
microbial!means!(increased!microbial!colonization!when!submerged!in!water![Glasby!and!
LLP2]!compared!to!when!on!a!relatively!dry!soil!surface![LLP1])!(Day!1983).!!The!higher!
decomposition!rates!for!filter!paper!compared!to!stem!tissue!shows!the!recalcitrant!nature!
of!the!stem!tissue!and!the!high!organic!matter!buildup!seen!in!Phragmites!stands!attests!to!
this:!the!more!labile!leaves!decompose!quickly!while!the!recalcitrant!stems!buildup!in!the!
soil!(Kominkova!et!al.!2000;!Agoston)Szabo!and!Dinka!2008).!!! !!!!!

129!

!

The!absence!of!potential!denitrification!at!Glasby!is!probably!due!to!the!low!nitrate!

levels!in!the!soil!(Figure!3)28;!Findlay!et!al.!2003;!Reddy!and!DeLaune!2008),!which!is!
likely!caused!by!previous!denitrification!that!already!removed!nitrate!from!the!soil/water!
column.!!Also,!the!soil!C:N!ratio!was!the!highest!at!Glasby!compared!to!LLP1!and!LLP2!
(Table!3)1)!and!soil!organic!matter!quality!has!been!shown!to!influence!denitrification!
rates!(Burford!and!Bremner!1975;!Reddy!and!DeLaune!2008).!The!most!consistently!high!
rates!of!denitrification!were!from!LLP2!and!can,!as!for!the!N!mineralization!rates,!be!
attributed!to!the!fluctuating!position!of!the!water!table!that!created!an!ideal!environment!
for!the!alternation!between!nitrification!and!denitrification!(McClain!et!al.!2003;!Jacinthe!et!
al.!2012).!!The!multiple!regression!analysis!showing!nitrate!concentration!and!soil!C:N!ratio!
as!significant!predictors!of!denitrification!further!supports!this!explanation!for!the!low!
denitrification!rates!at!Glasby,!as!Glasby!had!both!low!nitrate!concentrations!and!low!soil!
quality.!!!
!

Taken!together,!the!significant!effects!of!site!on!litter!bag!decomposition,!N!

mineralization/nitrification,!and!denitrification,!along!with!the!differences!in!soil!
characteristics!among!sites,!suggests!the!strong!influence!site!differences!can!have!on!
wetland!biogeochemical!cycling,!even!within!monospecific!stands!of!the!same!plant!
species.!!The!most!conspicuous!difference!among!sites!was!their!hydrology.!!The!
differences!in!hydrology!among!sites!likely!influenced!the!differences!seen!in!
biogeochemical!process!rates,!nutrient!availability!(particularly!nitrate),!soil!moisture,!soil!
organic!matter,!and!possibly!the!depth!of!the!belowground!biomass!placement!of!
Phragmites!(Table!3)1).!!Changes!in!hydrology!have!been!shown!to!alter!almost!every!
aspect!of!the!physical!and!chemical!nature!of!wetlands!(LaBaugh!1986;!van!der!Valk!2000).!!!

130!

The!BGB!differences!seen!among!sites!(highest!at!Glasby!and!LLP2,!compared!to!
LLP1)!unlikely!demonstrates!a!true!difference!in!BGB!production!because!AGB!was!
comparable!among!sites,!and!probably!suggests!Phragmites!places!most!of!its!BGB!close!to!
the!soil!surface!in!consistently!waterlogged!systems!to!avoid!anaerobic!soil!conditions.!!At!
LLP1,!where!the!water!table!was!consistently!below!the!soil!surface,!Phragmites!was!likely!
to!extend!its!BGB!well!below!the!top!30!cm!of!soil!to!scavenge!for!more!nutrients!without!
having!the!negative!effects!of!anaerobiosis.!!This!behavior!has!been!seen!in!other!plants;!for!
example,!Schwintzer!and!Lancelle!(1983)!showed!the!rooting!depth!and!root!morphology!
of!Myrica+gale,!a!shrub!found!in!peatlands,!was!dependent!on!the!depth!of!the!water!table!
with!roots!growing!more!horizontally!the!closer!the!water!table!was!to!the!soil!surface.!!!
Future!studies!should!further!examine!the!effects!of!flooding!regime!on!
biogeochemical!cycling!within!Phragmites!stands,!along!with!the!more!direct!effects!of!
flooding!regime!on!the!plasticity!of!Phragmites.!!Additionally,!this!study!only!looked!at!
biogeochemistry!within!Phragmites!stands,!but!should!be!expanded!to!include!other!
dominant!wetland!species!to!determine!species!identity!matters!on!the!hydrology!effects!
seen!in!this!investigation.!!Some!of!the!expected!effects!of!living!biomass!and!litter!of!
Phragmites!on!C!and!N!cycling!were!not!seen!in!this!study,!which!was!likely!a!consequence!
of!the!relatively!short!time!span!of!the!study.!!Replicating!this!study!over!a!longer!time!
scale,!e.g.,!5)15!years,!would!allow!for!more!gradual!effects,!such!as!changes!in!soil!OM!
quality!and!quantity,!to!occur.!!It!is!likely!that!longer!studies!would!find!that!living!
Phragmites!is!integral!to!maintaining!high!soil!OM!matter!content!usually!seen!under!
monospecific!stands!by!continual!inputs!of!litter!and!significant!soil!shading!that!decreases!
OM!decomposition.!!

131!

Chapter(4(
Effects(of(Litter(Quality,(Soil(Origin,(and(Plant(Species(Diversity(on(Decomposition(in(
Temperate(Wetlands(
!
Brief(Rationale(
!
The!chemical!and!physical!characteristics!of!plant!litter!have!been!shown!to!influence!
ecosystem!processes!in!many!environments!(Melillo!et!al.!1982;!McClaugherty!et!al.!1985;!
D’Antonio!and!Vitousek!1992;!Cornwell!et!al.!2008),!and!this!becomes!especially!apparent!
when!an!invasive!plant!becomes!abundant!in!a!new!environment.!!For!example,!invasion!of!
Bromus+tectorum+(cheatgrass)!into!the!arid!grasslands!of!the!Colorado!Plateau!(USA)!
decreased!N!mineralization!rates!due!to!the!significantly!greater!C:N!ratio!of!litter!inputs!
from!B.+tectorum!compared!to!native!species!(Evans!et!al.!2001).!!Species)specific!litter!
quality!(C:N,!lignin:N,!etc.)!can!influence!C!and!N!cycling!by!controlling!decomposition!rates!
(Ehrenfeld!2003;!Eviner!and!Chapin!2003;!Eviner!2004;!Orwin!et!al.!2008).!!Myrica+faya,!a!
nitrogen)fixer!that!invaded!young!volcanic!sites!on!Hawaii,!was!shown!to!enhance!N!
cycling!by!producing!N)rich!litter!that!decomposed!quickly!releasing!plant!available!N!
(Vitousek!et!al.!1987).!!Species)specific!differences!in!litter!quality!is!a!potentially!
important!aspect!of!invasions!by!exotic!plants!in!wetlands!because!often!the!invasive!
species!becomes!dominant!over!all!other!species.!Invasive!species!can!also!invade!into!
monospecific!stands!of!other!invasive!species,!though!the!effects!of!this!type!of!invasion!on!
biogeochemical!cycling!is!largely!unknown!!!
To!separate!species)specific!litter!quality!from!other!controls!on!decomposition!and!N!
transformation!rates,!I!performed!a!laboratory!incubation!using!both!litter!and!surficial!soil!
from!wetlands!with!nearly!monospecific!stands!of!three!widespread!invasive!wetland!
plants,!Phalaris+arundinacea,!Phragmites+australis,!and!Typha+ × glauca!(hereafter!Phalaris,!

132!

€

Phragmites,!and!Typha,!respectively),!as!well!as!from!an!additional!wetland+dominated!by+
Carex+lacustris!(a!native!sedge;!hereafter!Carex).!!The!sedge)dominated!wetland!represents!
a!community!that!has!not!been!invaded!and!hence!served!as!a!reference!relative!to!invaded!
plots.!!All!four!study!species!are!in!the!same!functional!group!(clonal,!emergent!wetland!
dominants;!Boutin!and!Keddy!1993),!so!if!significant!differences!are!found!among!species!
this!might!suggest!that!invasions!can!alter!carbon!cycling!even!if!the!plants!are!similar!in!
growth!form.!!!
Additionally,!few!studies!have!tried!to!determine!if!dominant!plant!species!invoke!
strong!soil!legacy!effects!(termed!“soil!origin!effects”!in!this!study)!that!can!influence!the!
decomposition!of!organic!matter!inputs.!!Soil!origin!effects!can!have!significant!influences!
on!C!and!N!cycling!independent!of!the!characteristics!of!the!litter!inputs!or!climate.!!The!
mechanisms!of!soil!origin!effects!can!range!from!differences!in!soil!microbial!community!to!
nutrient!availability!to!organic!matter!content.!!For!example,!soil!microbial!communities!
can!be!adapted!to!the!particular!physical!and!chemical!characteristics!of!the!litter!they!are!
accustomed!to!decomposing!(Gholz!et!al.!2000;!Strickland!et!al.!2009).!!This!has!been!
referred!to!as!“home)field!advantage”!(Ayres!et!al.!2009)!and!usually!results!in!higher!
decomposition!rates!of!resident!litter.!!If!dominant!plant!species!from!the!same!functional!
group!can!influence!C!and!N!cycling!by!species)specific!litter!and!soil!origin!effects,!then!
there!might!be!less!justification!for!categorizing!wetland!species,!especially!invasive!
species,!into!generalized!functional!groups.!!!
While!the!incubation!briefly!explained!above!explored!the!effects!of!litter!identity!and!
soil!source!on!C!and!N!mineralization,!I!also!was!interested!in!the!effects!of!litter!diversity!
on!C!and!N!mineralization.!!For!this,!I!conducted!a!second!incubation!experiment!in!which!I!

133!

mixed!different!combinations!of!litter!from!the!four!species!described!above!into!a!
common!soil.!!Litter!diversity!has!been!shown!to!enhance!decomposition!in!some!
experiments,!but!the!outcomes!of!mixing!are!not!always!predictable!from!single!species!
litter!treatments!(Blair!et!al.!1990;!Hector!et!al.!2000).!!Understanding!the!consequence!of!
litter!diversity!is!important!because!invasive!species!often!become!dominant!but!may!or!
may!not!form!monospecific!stands.!!In!most!cases,!plant!invasion!decreases!the!diversity!of!
litter!inputs!to!soil!systems!due!to!a!decrease!in!plant!species!diversity.!!If!litter!diversity!
were!correlated!with!decomposition!rates,!then!one!outcome!of!monospecific!stand!
formation!(and!hence!a!single!species!litter!layer)!would!be!a!reduction!in!overall!
decomposition!and!an!increase!in!organic!matter!buildup.!!In!other!words,!invasive!species!
would!decrease!decomposition!rates!when!they!reduce!species!(litter)!diversity.!!
!
Objectives,(Hypotheses,(and(Predictions(
Objective)1:(To!separate!species)specific!litter!quality!from!other!controls!on!C!and!N!
mineralization!rates!and!to!determine!if!dominant!wetland!species!“condition”!soil!
substrate.!
!
Hypothesis)1:(C!and!N!mineralization!rates!will!depend!not!only!on!the!species)specific!
quality!of!the!litter!(high!quality!=!high!mineralization!rates),!but!also!on!the!conditioning!
of!the!soil!by!the!dominant!species!(significant!soil!effect).!!As!a!result,!I!predict:!
!
1. The!four!study!species!will!vary!in!litter!quality!(C:N!ratio)!with!Phragmites!litter!
being!the!most!recalcitrant!(higher!C:N!ratio)!and!Carex+the!least!(lower!C:N!ratio)!

134!

2. There!will!be!a!negative!relationship!between!litter!C:N!ratios!and!C!and!N!
mineralization!rates!
3. After!background!soil!C!mineralization!rates!(based!on!soil!emissions!of!CO2!without!
added!litter)!are!factored!out!of!total!C!mineralization!(soil!+!litter!C!mineralization),!
there!will!still!be!a!significant!soil!effect,!indicating!a!soil!origin!effect.!!
!
Objective)2:!!To!determine!if!wetland!species!litter!diversity!influences!C!and!N!
mineralization.!This!is!an!important!component!of!the!biogeochemical!implications!of!
invasions!because!the!initial!stages!of!invasion!should!result!in!a!diverse!litter!layer,!with!C!
and!N!cycling!feedbacks!potentially!affecting!the!ability!of!the!invader!to!become!dominant.!
!
Hypothesis)2:!Mixtures!of!litter!from!different!dominant!wetland!species!will!have!higher!
decomposition!rates!compared!to!single!litter!type!additions!due!to!higher!substrate!
diversity.!!As!a!result,!I!predict:!
!
1. There!will!be!a!positive!relationship!between!litter!diversity!and!cumulative!C!
mineralization.!!!
2. Species)specific!litter!decomposition!rates!in!single!litter!treatments!will!predict!
which!litter!diversity!treatments!will!decompose!the!fastest,!e.g.,!the!two!species!
with!highest!decomposition!rates!in!single!litter!treatments!will!result!in!the!highest!
decomposition!rates!when!incubated!together.!!
(
(

135!

Methods(
Litter+quality+and+soil+origin+incubation+
The!laboratory!incubation!was!setup!as!a!4!x!5!factorial!treatment!design!and!was!
conducted!from!23!April!to!29!June!2010.!!Four!soil!origin!factor!levels!were!crossed!with!
five!factor!levels!of!species)specific!litter!for!a!total!of!20!treatment!combinations.!The!four!
soil!origin!levels!were!soil!collected!within!monospecific!stands!of!Phalaris,!Phragmites,!
Typha,!and!Carex.!!The!species)specific!litter!levels!were!the!same!four!species!as!the!soil!
origin!factor!with!the!addition!of!a!no!litter!addition!factor!level.!!Each!treatment!
combination!was!replicated!six!times!for!a!total!120!experimental!subjects!(120!incubation!
jars!=!4!soil!origin!levels!x!5!litter!levels!x!6!replicates).!!The!factorial!design!enabled!the!
detection!of!interactions!between!soil!origin!and!species)specific!litter,!as!well!as!the!
influence!of!soil!origin!identity!on!litter!decomposition.!
!
Site!description!and!sample!processing!
Soil!and!litter!samples!used!for!this!laboratory!incubation!were!collected!from!Lake!
Lansing!Park!North!(LLP)(42o46’07”N!85o23’32”W),!Haslett,!MI.!!Lake!Lansing!Park!North!
is!embedded!in!a!mosaic!of!lakes,!woodlots,!and!residential!areas.!!The!total!area!of!the!
park!is!166!hectares!and!consists!mainly!of!deciduous!forest,!coniferous!forest,!and!a!large!
interconnected!wetland!complex!of!approximately!70!hectares.!!The!park!has!been!
extensively!invaded!by!a!variety!of!invasive!plant!species,!including!Phalaris,!Phragmites,!
and!Typha.!!The!wetland!complex!has!become!a!mosaic!of!monospecific!stands!of!these!
three!species,!though!some!areas!are!mixtures!of!these!three!invasive!species!along!with!
some!native!species.!!Some!of!the!more!conspicuous!native!species!include!Carex!spp.,!

136!

Juncus!spp.,!Sambucus+canadensis,!Leersia+oryzoides,!Eutrochium!spp.,!Asclepias+incarnata,!
Echinocystis+lobata,!and!Impatiens+capensis.!!Litter!was!collected!from!monospecific!stands!
of!the!four!study!species,!Phalaris,!Typha,!Phragmites,!and!Carex+(Figure!4)1),!during!the!fall!
of!2009!after!all!plants!had!senesced,!but!before!the!first!snowfall!to!avoid!leaching.!!Carex,!
a!native!sedge,!was!used!in!this!experiment!because!it!has!a!tendency!to!form!monospecific!
stands!similar!to!the!invasive!plant!species!in!this!study!and!thus!allowed!for!the!
comparison!between!native!and!invasive!species!with!similar!growth!habits.!!Each!
monospecific!stand!was!greater!than!200!m2!and!at!least!90%!of!the!species!cover!was!of!
the!study!species.!Each!monospecific!stand!had!similar!hydrology:!early!spring!rain!would!
raise!water!levels!to!a!maximum!(<!1!m!above!ground),!and!by!the!end!of!the!growing!
season!the!water!level!was!below!the!soil!surface.!!!
Within!each!monospecific!stand,!fresh!species)specific!litter!(recently!senesced!and!
fallen)!was!collected!within!six!1)m2!plots!using!linear!transect!sampling!with!2.5!meters!
between!each!plot.!!In!Spring!2010,!six!10)cm!deep!cores!(166!cm3)!were!collected!directly!
adjacent!from!each!litter!sampling!plot!and!sealed!in!whirl)pak!plastic!bags!(Nasco),!
immediately!placed!on!ice,!and!transported!to!the!laboratory!where!they!were!kept!at!4°C!
for!2!days!until!the!start!of!the!incubation.!
After!being!stored!at!4°C!for!2!days,!I!sieved!(4!mm)!each!core!to!remove!large!roots!
and!rocks.!!Each!soil!core!was!then!sub)sampled!for!bulk!density!and!%!moisture!
determination!(60!g),!as!well!as!for!initial!nitrate!and!ammonium!concentration!
determination!(15!g,!see!below!for!N!mineralization/nitrification!methods).!!The!dry!mass!
of!the!60!g!sub)sample!was!measured!after!oven!drying!at!80°C!for!48!hours.!!Dried!soils!

137!

were!then!ground!and!homogenized!using!a!mortal!and!pestle!and!run!on!an!elemental!
combustion!system!(Costech!ECS!4010,!Valencia,!CA)!for!%C!and!%N!analysis.!!Samples!
were!run!in!duplicate!with!atropine!used!as!a!standard!every!10!samples.!!The!remaining!
wet!soil!was!then!split!into!five!subsamples!of!20!g!and!each!subsample!was!placed!into!a!
250!mL!incubation!jar!(Chromatographic!Specialties,!Inc.;!Ontario,!Canada).!!These!
incubation!soils!were!equilibrated!for!7!days!at!4°C!prior!to!litter!treatment!addition!to!
allow!the!C!mineralization!pulse!from!root!death!to!pass.!!Soil!C:N!ratios!are!expressed!on!a!
mass!basis.!
Litter!collected!at!each!monospecific!stand!was!air!dried!at!room!temperature!and!
stored!for!6!months!before!processing.!!All!litter!samples!taken!from!a!species)specific!
monospecific!stand!were!combined!and!mixed!to!homogenize!litter!characteristics.!!Litter!
was!then!separated!by!organ!(stems,!leaves,!and!inflorescences).!!Species)specific!organ!
subsamples!were!then!cut!by!hand!and!sieved!through!a!4)!and!2)mm!mesh.!!The!2!to!4!mm!
litter!pieces!were!used!in!the!experiment!to!ensure!contact!with!the!soil!within!each!
incubation!jar.!!For!each!species’!litter,!multiple!subsamples!were!taken!from!the!
homogenized!mixture!for!chemical!analysis.!!Litter!%C!and!%N!were!determined!on!an!
elemental!combustion!system!(see!above)!and!C:N!ratios!are!expressed!on!a!mass!basis.!!
!For!each!replicate!of!each!treatment!combination,!one!gram!of!litter!(1:1!ratio!of!
stems!to!leaves)!was!hand!mixed!into!the!soil!to!maximize!physical!contact!between!soil!
and!litter.!!Jars!were!then!allowed!to!equilibrate!for!3!days!and!were!sealed!with!lids!fitted!
with!septa!to!allow!room!air!to!enter!the!jar!until!the!start!of!a!CO2!sampling!round!(see!
below).!!All!jars!(120!total)!were!incubated!in!the!dark!for!68!days.!!Similar!soil!moisture!
conditions!were!created!across!all!incubation!samples!by!bringing!each!to!comparable!
138!

moisture!contents!before!the!beginning!of!the!experiment!(40)60%!representing!ideal!non)
limiting!conditions).!!Moisture!content!was!maintained!weekly!over!the!course!of!the!
incubation!by!adding!an!appropriate!volume!of!distilled!water!after!each!jar!was!weighed!
to!determine!water!loss.!
!
Carbon!mineralization!assay!
Carbon!mineralization!rates!were!estimated!during!seven!24)hour!periods!over!the!
68)day!incubation!(days!1,!4,!8,!13,!26,!41,!and!68).!!During!each!period,!a!10!mL!headspace!
gas!sample!was!taken!from!each!jar!immediately!after!jars!were!sealed!(time!=!0)!using!a!
three)way!stopcock)fitted!syringe,!and!then!after!6,!12,!and!24!hours.!!Before!gas!samples!
were!extracted,!each!jar!was!shaken!by!hand!to!mix!soil!pore!spaces!and!to!release!trapped!
gas!bubbles.!!After!headspace!samples!were!collected,!jars!were!backfilled!with!10!mL!of!N2!
gas!to!ensure!constant!air!pressure!and!volume.!!After!each!round,!lids!were!removed,!
samples!were!gently!flushed!with!ambient!air,!and!jars!were!wrapped!with!plastic!wrap!to!
prevent!moisture!loss.!!!
!

The!headspace!gas!samples!were!analyzed!for!CO2!concentrations!by!injecting!the!

10!mL!sample!into!a!PP)system!EGM)4!infrared!gas!analyzer!(IRGA).!!The!IRGA!was!
standardized!using!a!CO2!standard!gas!after!every!20!injections.!!Carbon!dioxide!
concentrations!were!corrected!for!headspace!dilution!caused!by!backfilling!with!N2!gas.!!
The!slope!of!CO2!concentrations!over!the!incubation!period!was!used!to!calculate!C!
mineralization!rates.!!No!slope!had!an!R2!value!of!less!than!0.85!and!the!majority!(>95%)!

139!

were!greater!than!0.95.!!CO2!production!was!assumed!to!be!due!to!C!mineralization!
(decomposition).!!!
The!C!mineralization!rates!for!litter!addition!treatments!were!background)corrected!
based!on!CO2!production!in!No!Litter!treatment!counterparts!(assumed!to!represent!
ambient!soil!C!mineralization)!for!the!particular!day!of!measurement,!and!then!divided!by!
litter!dry!weight!to!report!data!on!a!mass!basis!(g!CO2)C!kg)1!litter!C!day)1).!!!!First!order!
rate!constants!(k,!day)1)!were!calculated!by!taking!the!natural!log!(In)!of!the!C!
mineralization!rates!and!then!determining!the!slope!of!the!In!transformed!rates!over!the!
time!course!of!the!incubation.!!Total!CO2!production!was!calculated!by!fitting!a!nonlinear!
curve!(log)!to!the!time!course!of!rates!described!above,!then!interpolating!daily!CO2!
production!and!summing!these!values.!!
!
N!mineralization/nitrification!assay!
Initial!NO3)!and!NH4+!concentrations!were!determined!from!the!15!g!subsample!
collected!at!the!time!of!initial!soil!processing!using!the!KCl!extraction!method!(Robertson!
1999).!!After!the!68)day!incubation!period,!the!contents!of!each!jar!(litter!and!soil)!were!
extracted!for!final!NO3)!and!NH4+!concentrations!using!the!same!method.!!Concentrations!
of!NO3)!and!NH4+!in!the!extracts!were!analyzed!by!the!microplate!method!using!protocols!
developed!by!Dr.!David!Rothstein!(Dept.!of!Forestry,!MSU).!!Net!rates!of!N!mineralization!
and!nitrification!were!calculated!from!the!changes!in!inorganic!N!(NH4+!+!NO3))!or!NO3),!

140!

respectively,!during!the!incubation!period!(initial!–!final!pool!sizes/incubation!period).!!N!
mineralization!and!nitrification!rates!were!expressed!on!a!soil!mass!basis!similar!to!the!C!
mineralization!component!of!the!experiment.!
!
Litter+diversity+incubation+
The!litter!diversity!incubation!was!designed!as!a!single!factor!treatment!structure!
and!was!conducted!from!1!December!2010!to!24!January!2011.!!The!single!factor!of!
species)specific!litter!diversity!consisted!of!16!factor!levels!of!different!combinations!of!
litter!collected!from!monospecific!stands!of!Phalaris,!Phragmites,!Typha,!and!Carex.!!The!16!
treatment!levels!consisted!of!all!possible!species!combinations!within!a!litter!diversity!level!
and!were!as!follows:!single!species!(4),!two!species!(6),!three!species!(4),!all!species!(1)!and!
no!litter!(1).!!A!replacement!design!(as!opposed!to!an!additive!design)!was!used!for!litter!
mixtures!(see!below).!!All!litter!treatment!levels!were!incubated!in!a!“common!soil”,!
meaning!the!soil!was!not!collected!from!a!monospecific!stand!of!any!of!the!four!species.!!
Instead,!the!soil!was!collected!from!a!shallow,!unvegetated!ephemeral!pond!to!minimize!
the!possible!conditioning!effects!plant!species!could!have!on!the!soil.!!Each!treatment!level!
was!replicated!seven!times!for!a!total!112!experimental!subjects!(incubation!jars).!!This!
experimental!design!was!developed!to!test!the!effects!of!wetland!species!litter!diversity!on!!
C!and!N!transformation!rates.!
!
Site!description!and!sample!processing!
Soil!and!litter!samples!used!for!this!laboratory!incubation!were!collected!from!Lake!
Lansing!Park!North,!within!the!same!wetland!complex!used!for!the!soil!origin!incubation!

141!

described!above!(Figure!4)1).!!Litter!was!collected!using!the!same!protocol!and!from!the!
same!monospecific!stands!of!the!four!study!species!as!in!the!soil!origin!incubation.!!During!
the!fall!of!2010,!litter!was!collected!after!all!plants!had!senesced,!but!before!the!first!
snowfall!to!avoid!leaching.!!Within!a!unvegetated!ephemeral!wetland,!twenty!10)cm!deep!
soil!cores!(166!cm3)!were!collected!during!fall!2010!using!linear!transect!sampling!with!
one!meter!between!each!core.!These!soil!cores!were!sealed!in!whirl)pak!bags!(Nasco),!
immediately!placed!on!ice,!and!transported!to!the!laboratory!where!they!were!kept!at!4°C!
for!2!days!until!the!start!of!the!incubation.!!
After!being!stored!at!4°C!for!2!days,!each!core!was!sieved!(4!mm)!to!remove!large!
roots!and!rocks.!!Each!sieved!soil!core!was!then!combined!and!homogenized!in!a!large!
plastic!container.!!Eighteen!sub)samples!(30!g)!were!taken!for!bulk!density!and!%!moisture!
determination,!and!eighteen!more!subsamples!were!taken!for!initial!nitrate!and!
ammonium!concentration!determination!(15!g,!see!below!for!N!mineralization/nitrification!
methods).!!The!dry!mass!of!the!eighteen!30!g!sub)samples!was!measured!by!oven!drying!at!
80°C!for!48!hours.!!Dried!soils!were!then!ground!and!homogenized!using!a!mortal!and!
pestle!and!run!on!an!elemental!combustion!system!(Costech!ECS!4010,!Valencia,!CA)!for!
%C!and!%N!analysis.!!Samples!were!run!in!duplicate!with!atropine!used!as!a!standard!
every!10!samples.!!From!the!homogenized!wet!soil,!112!30)g!subsamples!were!placed!into!
separate!250!ml!incubation!jars!(Chromatographic!Specialties,!Inc.;!Ontario,!Canada).!!
These!incubation!soils!were!equilibrated!for!7!days!at!4°C!prior!to!litter!treatment!addition!
to!allow!the!C!mineralization!pulse!from!root!death!to!pass.!!Litter!collected!at!each!
monospecific!stand!was!air!dried!at!room!temperature!for!two!weeks!before!processing.!!
Litter!%C!and!%N!were!determined!on!an!elemental!combustion!system,!while!%lignin!
142!

was!determined!by!near!infrared!reflectance!spectrophotometry!(samples!analyzed!by!
Litchfield!Analytical!Services,!MI;!McLellan!et!al!1991).!!!
The!remaining!litter!processing!was!carried!out!as!in!soil!origin!incubation.!!For!
each!replicate!of!each!treatment!level,!2!g!of!litter!was!hand!mixed!into!the!common!soil!to!
maximize!physical!contact!between!soil!and!litter.!!As!mentioned!above,!litter!was!added!
within!a!replacement!design,!as!opposed!to!an!additive!design.!!The!same!total!amount!of!
litter!was!added!to!each!incubation!jar!regardless!of!litter!diversity!treatment,!e.g.,!2!g!of!
Phragmites!litter!was!added!for!the!single!species!additions,!but!for!the!two!species!litter!
addition!of!Phragmites!and!Phalaris,!1!g!of!each!was!added.!!A!replacement!design!was!used!
to!keep!the!total!amount!of!litter!the!same!because!changing!the!amount!of!total!litter!
added!would!alter!the!decomposition!rates!and!would!confound!any!diversity!effects.!!The!
stem:leaf!ratio!of!added!litter!differed!among!species!(3:1!ratio!for!Phalaris!and!Phragmites!
and!1:1!ratio!for!Typha!and!Carex)!in!this!experiment!to!approximate!stem:leaf!ratios!that!
occur!in!the!field.!!Jars!were!then!allowed!to!equilibrate!for!3!days!after!which!they!were!
loosely!sealed!with!lids!(fitted!with!septa)!to!allow!room!air!to!enter!the!jar!until!the!start!
of!a!CO2!extraction!round!(see!below).!!All!jars!(112!total)!were!incubated!in!the!dark!for!
55!days.!!Non)limiting!soil!moisture!conditions!were!created!similar!to!the!soil!origin!
incubation.!
!
Carbon!mineralization!assay!
Carbon!mineralization!rates!were!estimated!during!six!24)hour!periods!over!the!55)
day!incubation!(days!1,!3,!7,!15,!29,!and!55).!!I!estimated!CO2!production!and!C!

143!

mineralization!rates!following!the!same!methods!as!outlined!in!incubation!1!(litter!quality!
and!soil!origin!incubation).!!No!slope!had!an!R2!value!of!less!than!0.85!and!the!majority!
(>95%)!were!greater!than!0.90.!!The!C!mineralization!rates!for!litter!addition!treatments!
were!background)corrected!based!on!the!No!Litter!treatment!for!a!particular!day!of!
measurement!and!then!divided!by!litter!dry!weight!to!report!data!on!a!mass!basis!(g!CO2)C!
kg)1!litter!C!day)1).!!!!First!order!rate!constants!(k,!day)1)!and!total!CO2!production!were!
calculated!as!in!the!soil!origin!incubation.!
!
N!mineralization/nitrification!assay!
Initial!NO3)!and!NH4+!concentrations!were!determined!from!the!15!g!subsample!
collected!at!the!time!of!initial!soil!processing!using!the!KCl!extraction!method!(Robertson!
1999).!!After!the!55)day!incubation!period,!the!contents!of!each!jar!(litter!and!soil)!were!
extracted!for!final!NO3)!and!NH4+!concentrations!using!the!same!method.!!Concentrations!
of!NO3)!and!NH4+!in!the!extracts!were!analyzed!by!the!microplate!method!using!protocols!
developed!by!Dr.!David!Rothstein!(Dept.!of!Forestry,!MSU).!!Net!rates!of!N!mineralization!
and!nitrification!were!calculated!from!the!changes!in!inorganic!N!(NH4+!+!NO3))!or!NO3),!
respectively,!during!the!incubation!period!(initial!–!final!pool!sizes/incubation!period).!!N!
mineralization!and!nitrification!rates!were!calculated!on!a!soil!mass!and!soil!carbon!basis!
similar!to!the!C!mineralization!component!of!the!experiment.!
!
!
144!

Statistical+analysis+
General!linear!models!(GLMs)!were!used!to!test!for!treatment!effects!on!first!order!
rate!constants,!total!C!mineralization,!N!mineralization,!and!nitrification.!!Species!effects!on!
soil!%C,!%N,!and!C:N!ratio!and!litter!chemistry!(%C,!%N,!C:N!ratio,!%lignin,!lignin:N!ratio)!
were!determined!using!GLMs.!!Tukey’s!HSD!multiple!comparison!tests!were!performed!to!
determine!significant!differences!between!factor!levels.!!To!determine!the!relationship!
between!litter!diversity!and!total!C!mineralization,!a!regression!analyses!was!performed!
with!litter!diversity!treatments!1!though!4!as!the!independent!factor.!!Simple!linear!
regression!was!used!to!investigate!both!soil!and!litter!quality!controls!on!C!and!N!
mineralization!rates.!!Model!diagnostics!were!assessed!for!each!analysis!to!determine!if!the!
residuals!were!normally!distributed!and!displayed!constant!error!variances.!!Log!
transformations!were!used!to!correct!for!any!heteroscedasticity.!!All!statistical!tests!were!
performed!in!R!2.13.2!(R!Development!Core!Team!2011).!!!
!
!
!
!
!
!
!
!
!
!

145!

0

0.5

1 km

±
_[
[_
Phr

Pha
Typ

_
[

_
[

Lake
Lansing

Car

Figure!4)1.!Map!showing!the!location!of!the!monospecific!stands!of!Phragmites+australis+
(Phr),+Phalaris+arundinacea+(Pha),+Typha × glauca+(Typ),+and+Carex+lacustris!(Car)!in!the!
wetland!area!within!Lake!Lansing!Park!North,!Haslett,!MI.!
!
!

€

!
!
!
!
(
(
(
146!

!

Results(
Litter+quality+and+soil+origin+incubation+
First!order!rate!constants!(k,!decomposition!rate)!varied!among!treatment!
combinations,!with!the!highest!rate!constant!occurring!when!Phragmites!litter!was!
incubated!in!Phalaris!soil!(0.0282!±!0.012!day)1)!and!the!lowest!when!Typha!litter!was!
incubated!in+Carex!soil!(0.0085!±!0.003!day)1)!(Table!4)1).!!For!a!species)specific!litter!type,!
there!was!a!general!pattern!of!the!highest!decomposition!rate!occurring!when!incubated!in!
Phragmites!soil,!followed!by!Phalaris,!Typha,!and!Carex,!except!for!Phragmites!litter!which!
showed!no!pattern!among!the!soil!it!was!incubated!in!(marginal!litter!x!soil!interaction;!p!=!
0.068).!!Averaged!over!soil!origin,!Phragmites!litter!had!the!highest!decomposition!rate!and!
Typha+litter!the!lowest!(main!effect!of!litter;!p!<!0.001;!Table!4)2).!!The!only!treatment!
combination!that!had!a!comparable!decomposition!rate!compared!to!Phragmites!litter!was!
Phalaris!litter!when!incubated!in!Phragmites!soil.!!When!decomposition!rates!were!
averaged!over!species)specific!litter!type,!Carex!soil!had!the!lowest!and!Phragmites!soil!the!
highest!(main!effect!of!soil!origin;!p!<!0.001;!Table!4)2)!!
!

Phragmites!and!Phalaris!litter!had!the!highest!total!carbon!mineralization!rates!(C)

min),!followed!by!Carex!and!then!Typha!when!averaged!across!soil!origin!(Figure!4)2;!
significant!main!effect!of!litter;!p!<!0.001;!Table!4)2).!!When!averaged!across!species)
specific!litter,!soil!collected!under!monospecific!stands!of!Typha!and!Carex!had!the!greatest!
total!C)min,!followed!by!Phalaris!and!then!Phragmites!(Figure!4)2;!significant!main!effect!of!
soil!origin;!p!<!0.001;!Table!4)2).!!Overall,!the!treatment!combination!that!yielded!the!
highest!C)min!was!Phalaris!litter!incubated!with!Typha!soil,!whereas!Typha!litter!incubated!

147!

with!Phragmites!soil!yielded!the!lowest!C)min.!!The!interaction!between!species)specific!
litter!and!soil!origin!was!not!significant.!!The!significant!effect!of!soil!origin!on!total!C)min!
after!background!C)min!attributed!to!soil!alone!was!factored!out!suggests!the!importance!
of!soil!origin.!
!

There!were!significant!species!effects!on!soil!%C,!%N,!and!C:N!ratio!(Table!4)3).!!

Phragmites!soil!had!the!highest!soil!C:N!ratio!(significant!main!effect!of!species;!p!<!0.001;!
Table!4)3),!indicating!that!the!quality!of!its!soil!organic!matter!was!poorer!compared!to!
soils!of!different!species!origin,!and!this!is!consistent!with!total!C)min!results!suggesting!
Phragmites!soil!organic!matter!was!the!least!labile.!!Phalaris!and!Carex!soil!had!
intermediate!soil!C:N!ratios!with!Carex!soil!C:N!ratios!significantly!greater!than!that!of+
Typha.!!Soils!collected!from!monospecific!stands!of!Phalaris!and!Typha!had!the!highest!soil!
%C!and!%N,!while!soils!collected!from!Phragmites!and!Carex!had!the!lowest!C:N!ratios,!and!
for!soil!%N,!Phragmites!had!significantly!less!than!Carex!(significant!species!effect;!p!<!
0.001;!Table!4)3).!!!
Litter!N!content!significantly!differed!among!species.!!Typha!and!Carex!litter!had!the!
highest!litter!C:N!ratios!at!~!65,!followed!by!Phalaris!at!~!40!and!Phragmites!at!~28!
(significant!species!effect;!p!<!0.001;!Table!4)3).!!For!litter!%N,!Phragmites!litter!contained!
the!greatest!amount,!followed!by!Phalaris!and!then!Typha!and!Carex,!which!were!not!
significantly!different!from!each!other!(significant!species!effect;!p!<!0.001;!Table!4)3).!!A!
different!pattern!arose!for!litter!%C;!Phalaris!and!Typha!litter!had!the!highest!%C,!followed!
by!Carex!litter!and!finally!Phragmites!(significant!species!effect;!p!<!0.001;!Table!4)3).!!
Phragmites!litter!had!the!lowest!C:N!ratios!due!both!to!the!highest!litter!%N!and!the!lowest!
litter!%C!among!all!species.!

148!

!

Past!studies!have!shown!that!soil!and!litter!C:N!ratio!(indicators!of!quality)!can!have!

significant!controlling!effects!on!decomposition!rates!(Melillo!et!al.!1982;!Taylor!et!al.!1989,!
Berg!2000).!!To!test!this,!simple!linear!regression!was!used!to!determine!if!a!relationship!
between!total!C)min!and!either!litter!or!soil!C:N!ratio!existed.!!There!was!no!relationship!
between!total!C)min!and!soil!C:N!ratio!when!all!treatment!combinations!were!included!in!
the!analysis!(Figure!4)3;!adjusted!R2!=!0.003,!p!=!0.423),!nor!was!this!relationship!
significant!when!all!litter!addition!treatment!combinations!were!removed!and!only!No!
Litter!addition!(soil!only)!treatments!were!analyzed!(Figure!4)4;!adjusted!R2!=!0.077,!p!=!
0.105).!!There!was!a!significant!positive!relationship!between!total!C)min!(No!Litter!
treatments!only)!and!soil!%N!(Figure!4)5;!adjusted!R2!=!0.192,!p!=!0.018).!!For!litter!
addition!treatments,!litter!C:N!ratio!had!a!negative!relationship!with!total!C)min!(Figure!4)
6;!total!C)min;!adjusted!R2!=!0.524,!p!<!0.001),!though!the!relationship!was!much!stronger!
at!the!beginning!of!the!incubation!(Figure!4)7;!Day!1!C)min;!adjusted!R2!=!0.861,!p!<!0.001).!!
These!data!indicate!that!the!influence!of!litter!quality!on!C)min!decreased!throughout!the!
incubation.!
!

Net!N!mineralization!and!nitrification!rates!were!almost!identical!to!each!other!

because!the!majority!of!the!ammonium!mineralized!was!nitrified!to!nitrate;!therefore!only!
net!N!mineralization!(N)min)!rates!will!be!discussed.!!Similar!to!total!C)min,!only!the!main!
effects!of!soil!origin!and!species)specific!litter!were!significant,!not!their!interaction!(Figure!
4)8;!p!<!0.001!for!both;!Table!2).!!Both!positive!and!negative!N)min!rates!were!found,!
indicating!N!immobilization!occurred!in!some!treatment!combinations!(negative!N)min!
rates).!!For!the!No!Litter!addition!treatments,!all!soil)origin!treatment!levels!had!positive!N)
149!

min!rates,!with!Phragmites!and!Typha!soil!having!the!highest!and!Phalaris!and!Carex!having!
the!lowest!rates.!!Phragmites+litter!was!the!only!litter!addition!treatment!level!that!resulted!
in!positive!N)min!rates!for!all!soil!origins!(it!also!had!the!lowest!litter!C:N!ratio:!Figure!4)8).!!
Among!soils!that!Phragmites!litter!was!incubated!in,!Phragmites!and!Typha!soil!resulted!in!
the!highest!N)min!rates,!while!Phalaris!and!Carex!soil!resulted!in!the!lowest.!!For!other!
litter!types!(Phalaris,!Typha,!and!Carex)!most!of!the!N)min!rates!were!negative,!except!for!
when!Phalaris!litter!was!incubated!in!Typha!soil,!which!resulted!in!positive!values!that!
were!comparable!to!low!values!for!Phragmites!litter.!!Regression!analysis!was!used!to!
determine!the!relationship!between!N)min!rates!and!litter!C:N!ratio!and!a!significant!
negative!curvilinear!relationship!was!found!(Figure!4)9;!R2!=!0.407,!p!<!0.001).!!No!
significant!relationship!was!found!for!N)min!rates!and!soil!C:N!ratio.!!These!results!suggest,!
as!for!C)min,!litter!C:N!ratio!partially!controlled!N)min!rates.!
!
Litter+diversity+incubation+
Among!single!species!litter!addition!treatments,!Phragmites!litter!had!the!lowest!
decomposition!rate!constant!and!Phalaris!litter!the!highest!(treatment!effect;!p!<!0.001;!
Tables!4)4!and!4)5).!!For!the!double!species!litter!addition!treatments,!all!litter!mixtures!
that!included!Phragmites!litter!had!the!lowest!decomposition!rate!compared!to!all!other!
litter!combinations.!!There!were!no!differences!among!triple!litter!addition!species!
mixtures,!which!also!were!not!different!from!the!non)Phragmites!double!species!litter!
mixtures!and!the!all!species!litter!mixture.!!!!

150!

Total!C)min!varied!among!litter!addition!treatments!(overall!mean:!271!g!CO2)C!kg)1!
litter!C)!with!the!greatest!difference!being!between!Typha!litter!addition!and!Phragmites!+!
Phalaris!litter!addition!(Figure!4)10;!significant!treatment!main!effect;!p!<!0.001;!Table!4)
5).!!Single!or!multiple!species!additions!that!included!Typha!litter!had!the!lowest!total!C)
min,!while!litter!mixtures!that!included!Phalaris!usually!had!the!highest!total!C)min.!!For!
the!single!litter!addition!treatments,!Carex!litter!had!the!greatest!total!C)min!and!Typha!
litter!the!least.!!The!treatment!with!the!greatest!total!C)min!was!the!two!species!litter!
addition!of!Phragmites!and!Phalaris,!which!was!significantly!greater!than!when!either!of!
these!two!species!were!incubated!alone,!indicating!the!possibility!of!a!non)additive!
relationship!between!these!two!types!of!litter.!!Though!there!was!not!a!strong!effect!of!
litter!diversity!on!total!C)min,!there!was!an!observable!decrease!in!the!variance!of!total!C)
min!as!litter!diversity!increased.!
Soil!used!in!this!incubation,!which!was!collected!from!the!ephemeral!pond!at!LLP,!
had!a!%C!of!23.29!(±!0.36),!a!%N!of!1.72!(±!0.03),!and!a!C:N!ratio!of!13.51!(±!0.09).!!Litter!
C:N!ratios!were!higher!and!differed!among!species;!Phalaris!and!Typha!had!the!highest!C:N!
ratio!at!~!62.5!and!Phragmites!had!the!lowest!C:N!ratio!at!47.2!(significant!species!effect;!p!
<!0.001;!Table!4)6).!!Percent!lignin!and!lignin:N!ratios!followed!a!similar!pattern!among!
species.!!The!highest!%!lignin!was!observed!in!Typha!litter,!with!Carex!and!Phalaris!having!
the!lowest!%!lignin!and!Phragmites,!Phalaris,!and!Carex!having!lower!lignin:N!ratio!than!
Typha!(significant!species!effect;!p!<!0.001;!Table!4)6).!
Simple!linear!regression!analysis!for!total!C)min!on!litter!C:N!ratios!showed!a!much!
weaker!negative!relationship!than!for!the!litter!quality!and!soil!origin!incubation,!though!
the!relationship!was!still!significant!(Figure!4)11;!adjusted!R2!=!0.131,!p!<!0.001).!!The!
151!

relationship!between!total!C)min!and!%!lignin!was!somewhat!stronger!(Figure!4)12;!
adjusted!R2!=!0.228,!p!<!0.001)!and!the!relationship!between!total!C)min!and!lignin:N!ratio!
was!the!best!fit!among!all!the!litter!quality!predictors!(Figure!4)13;!R2!=!0.313,!p!<!0.001).!!!
Litter!diversity!did!not!have!a!large!impact!on!total!C)min,!though!the!relationship!was!
significant!(Figure!4)14;!adjusted!R2!=!0.075,!p!=!0.002),!and!as!mentioned!before,!there!
was!a!reduction!in!the!variance!of!total!C)min!as!litter!diversity!increased.!!
As!with!the!litter!quality!and!soil!origin!incubation,!net!N!mineralization!rates!
mirrored!net!nitrification!rates,!therefore,!only!N)min!rates!will!be!discussed.!!The!only!
treatment!that!had!positive!N)min!rates!was!the!No!Litter!addition!treatment,!the!
remaining!litter!addition!treatment!levels!all!had!negative!N)min!rates,!indicating!net!N!
immobilization!(Figure!4)15;!significant!litter!treatment!effect;!p!<!0.001;!Table!4)5).!!
Though!the!No!Litter!addition!treatment!was!significantly!different!from!all!litter!addition!
treatment!levels,!none!of!the!litter!addition!treatments!were!statistically!distinct!from!the!
rest.!!The!consistent!trend!for!N!immobilization!for!each!litter!addition!treatment!level!can!
be!explained!in!the!same!way!as!the!soil!origin!incubation,!even!though!the!same!species)
specific!litter!was!used!in!both!incubations.!
!

!

!
!
!
!
!

152!

Table!4(1.!Average!decomposition!rates!expressed!as!first(order!rate!constants!(k;!day(1)!for!each!litter!x!
soil!origin!treatment!combination.!
Soil!Addition!
Litter!Addition!
!
!
!
!
!
!
Std.!
Std.!
Std.!
Std.!
!
Phragmites+ Error! Phalaris+
Error!
Typha+
Error!
Carex+
Error!
Phragmites+
0.0264!
0.011!
0.0267!
0.011!
0.0160!
0.007!
0.0218!
0.009!
Phalaris+
0.0282!
0.012!
0.0221!
0.009!
0.0143!
0.006!
0.0166!
0.007!
Typha+
0.0266!
0.011!
0.0175!
0.007!
0.0138!
0.006!
0.0170!
0.007!
Carex+
0.0253!
0.010!
0.0159!
0.006!
0.0085!
0.003!
0.0147!
0.006!
!
!
!
!
!
!

153!

!
Table!4(2.!Summary!of!the!two(factor!ANOVAs!for!the!effect!of!species(
specific!litter!and!soil!on!decomposition!constant!(K),!cumulative!C!
mineralization,!and!N!mineralization.!!
!
!
Source!
num!df!
!
!
K"constants"
!
"
!
Soil!
3!
!
!
Litter!
3!
!
!
Soil!x!Litter!
9!
!
!
Cumulative"C"
mineralization"
"
!
Soil!
3!
!
!
Litter!
3!
!
!
Soil!x!Litter!
9!
!
!
N"Mineralization"
"
!
Soil!
3!
!
!
Litter!
4!
!
!
Soil!x!Litter!
12!
!!
!!

!

!

!

den!df!
!
!
!
80!
!
80!
!
80!
!

!!

F!
!
!
!
12.35!
!
51.12!
!
1.87!
!

P>F!
!
!
!
<0.0001!
!
<0.0001!
!
0.0683!
!

!
!
80!
!
80!
!
80!
!
!
!
100!
!
100!
!
100!

!
!
11.29!
!
69.43!
!
1.60!
!
!
!
14.07!
!
92.30!
!
0.97!

!
!
<0.0001!
!
<0.0001!
!
0.1283!
!
!
!
<0.0001!
!
<0.0001!
!
0.4871!

!

154!

!!

!!

!
!
!
!
!
!
!
!
!
!

Table!4(3.!Soil!and!litter!%C,!%N,!and!C:N!mass!ratios!of!the!four!species!used!in!the!litter!quality!
and!soil!origin!incubation.!!Same!letter!superscript!denotes!nonsignificant!differences!according!to!
Tukey!post!hoc!tests.!Values!are!means!±!SE.!
Species!
Soil!%C!
Soil!%N!
Soil!C:N!
Litter!%C!
Litter!%N!
Litter!C:N!
Phragmites+

24.8!±1.07a!

1.78!±0.10a!

14.0!±0.32a!

41.4!±0.15a!

1.48!±0.01a!

28.0!±0.32a!

Phalaris+

40.22!±0.39b!

3.10!±0.03b!

13.0!±0.08b!

45.6!±0.14b!

1.14!±0.03b!

40.0!±0.94b!

Typha+

39.10!±3.62b!

3.13!±0.28b!

12.4!±0.17c!

45.5!±0.18c!

0.62!±0.01b!

74.3!±1.37c!

Carex+

31.13!±1.09c!

2.37!±0.09c!

13.1!±0.07b!

43.1!±0.16c!

0.62!±0.01c!

69.8!±1.51c!

155!

!
Table!4(4.!Average!decomposition!rates!expressed!as!first(order!rate!constants!(k;!
day(1)!for!each!litter!diversity!treatment.!
Litter!
Standard!
k!constant!(day(1)! Error!
Diversity!!
Species!
1!
Phalaris(
0.0222!
0.0084!
1!
Typha(
0.0191!
0.0072!
1!
Phragmites(
0.0173!
0.0066!
1!
Carex(
0.0206!
0.0078!
2!
Phragmites(+(Phalaris(
0.0192!
0.0072!
2!
Phragmites(+Typha(
0.0212!
0.0080!
2!
Phragmites(+(Carex(
0.0211!
0.0080!
2!
Phalaris(+(Typha(
0.0239!
0.0090!
2!
Phalaris(+(Carex(
0.0249!
0.0094!
2!
Typha(+(Carex(
0.0240!
0.0091!
3!
Phragmites(+(Phalaris(+(Typha(
0.0227!
0.0086!
3!
Phragmites(+(Phalaris(+(Carex(
0.0232!
0.0088!
3!
Phragmites(+(Typha(+(Carex(
0.0223!
0.0084!
3!
Phalaris(+(Typha(+(Carex(
0.0241!
0.0091!
4!
All!Species!Litter!
0.0233!
0.0088!
!
Table!4(5.!Summary!of!ANOVAs!for!the!effect!of!Treatment!on!decomposition!(K)!
constant,!cumulative!C!mineralization,!and!N!mineralization.!
!
Response!!
K!Constant!
Cumulative!C!
mineralization!
N!mineralization!
!

!

num!df!
14!

!

14!
15!

den!df!
90!
90!
96!

Table!4(6.!Litter!C:N!mass!ratios,!%!lignin,!and!lignin:N!
mass!ratios!of!the!four!species!used!in!the!litter!
diversity!incubation.!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!
tests.!Values!are!means!±!SE.!
Species!
C:N!
%!Lignin!
Lignin:N!
Phragmites(

47.2!±0.03a!

11.1!±0.40a!

12.4!±0.45a!

Phalaris(

62.0!±1.10b!

8.9!±0.24b!

12.6!±0.47a!

Typha(

63.0!±0.81b!

13.7!±0.02c!

19.1!±0.20b!

Carex(

53.7!±2.0c!

10.0!±0.30b!

12.1!±0.10a!

156!

!

F!
2.50!
8.08!
845.21!

!

P>F!
0.0047!
<0.0001!
<0.0001!

!
!
Phragmites"Soil"
Phalaris"Soil"
Typha"Soil"
Carex"Soil"
c
bc
b

800"

Total&C&Min&(g&CO2/C&kg/1&li2er&C)&

700"

a

a
a

a

a

a
c

600"
b

500"
400"

e

e

e

e

300"
d

200"
100"
0"
Phragmites"

Phalaris"

Typha"

Carex"

Species&Li2er&

!
Figure!4)2.!!Mean!cumulative!C!mineralization!over!the!68)day!litter!quality!and!soil!origin!laboratory!
incubation.!!The!main!effects!of!species)specific!litter!(F3,80!=!69.43,!p!<!0.001)!and!soil!origin!(F3,80!=!11.29,!p!<!
0.001)!were!significant,!but!not!their!interaction.!!Same!letter!superscript!denotes!nonsignificant!differences!
according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!
!

157!

Total&C&Min&(g&CO2/C&g/1&SC)&&

!
!
350"
300"
250"
200"
150"
100"
50"
0"
11.5"

12.5"

13.5"

14.5"

15.5"

Total&C&Min&(g&CO2/C&g/1&SC)&&

Soil&C:N&Ra6o&
!
Figure!4)3.!!Regression!between!soil!C:N!ratio!and!cumulative!C!mineralization!(all!
treatments)!(adjusted!R2!=!0.003,!p!=!0.423).!
!
!
80"
70"
60"
50"
40"
30"
20"
10"
0"
11.5"

12.5"

13.5"

14.5"

Soil&C:N&Ra6o&

15.5"

!
Figure!4)4.!!Regression!between!soil!C:N!ratio!and!cumulative!C!mineralization!(no!litter!
treatments!only)!(adjusted!R2!=!0.077,!p!=!0.105).!
!
!

158!

Total&C&Min&(g&CO2/C&g/1&SC)&&

80"
70"
60"
50"
40"
30"
20"
10"
0"
1"

1.5"

2"

2.5"

3"

3.5"

4"

Soil&%N&

Total&C&Min&(g&CO2/C&&kg/1&li9er&C)&&

!
Figure!4)5.!!Regression!between!soil!%N!ratio!and!cumulative!C!mineralization!(no!litter!
treatments!only)!(adjusted!R2!=!0.192,!p!=!0.018).!
!
!
900"
800"
700"
600"
500"
400"
300"
200"
100"
0"
22"

32"

42"

52"

62"

Li9er&C:N&Ra6o&

72"

82"

!
Figure!4)6.!!Regression!between!litter!C:N!ratio!and!cumulative!C!mineralization!(litter!
addition!treatments!only)!(adjusted!R2!=!0.524,!p!<!0.001).!
!
!

159!

Day&1&C&Min&(g&CO2/C&kg/1&li9er&C)&&

40"
35"
30"
25"
20"
15"
10"
5"
0"
22"

32"

42"

52"

62"

Li9er&C:N&Ra6o&

72"

82"

!
Figure!4)7.!!Regression!between!litter!C:N!ratio!and!day!1!C!mineralization!(Litter!addition!
treatments!only)!(adjusted!R2!=!0.861,!p!<!0.001).

160!

!
7#

Net$N$Mineraliza,on$(mg$N$kg21$soil$day21)$

6#

Phalaris#Soil#

a

Typha#Soil#
5#
4#
3#

a

Phragmites#Soil#

a

Carex#Soil#
b

a
e

e

b
b

2#
1#

c

cd
c

0#

d

c d

d

c d d d

!1#
!2#

Phragmites

Phalaris

Typha
Li9er$Type$

Carex

No Litter

!
Figure!4)8.!!Mean!net!N!mineralization!over!the!68)day!litter!quality!and!soil!origin!laboratory!incubation.!!The!main!
effects!of!species)specific!litter!(F3,100!=!92.30,!p!<!0.001)!and!soil!origin!(F12,100!=!14.07,!p!<!0.001)!were!significant,!
but!not!their!interaction.!!Same!letter!superscript!denotes!nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!
Error!bars!represent!1!SE.!!
!

161!

Net$N$Min$(mg$N$kg,1$soil$day,1)$

!
!
!
!
!
!
!
!
!
!
8#
6#
4#
2#
0#
!2#
!4#
20#

30#

40#

50#

60#

Li6er$C:N$Ra;o$

70#

80#

!
Figure!4)9.!Regression!between!litter!C:N!ratio!and!net!N!mineralization!(adjusted!R2!=!
0.452,!p!<!0.001).!
!
!
!
!
!
!
!

162!

!

350"

c

300"
250"

ab

ac

a

a

a

ab

ab

ab
b

b

ab

ab
ab

b

200"
150"
100"
50"

Ph
a"
ra
gm
ite
s"
Ca
re
Ph
x"
ra
g"+
"P
Ph
ha
ra
l"
g"+
Ty
Ph
ph
ra
g"+ a"
"C
ar
Ph
ex
al
"
"+
"Ty
ph
Ph
a"
al
"+
"C
Ty
ar
e
ph
Ph
a"+ x"
ra
g"+
"C
ar
"P
ex
ha
Ph
"
l "+
ra
"Ty
g"+
ph
"P
Ph
ha
a"
ra
l "+
g"+
"C
"Ty
ar
e
ph
Ph
a"+ x"
al
"+
"C
"Ty
ar
e
ph
a"+ x"
Al
"C
l"S
ar
pe
ex
cie
"
s"L
i=
er
"

Ty
ph

la
ris
"

0"
Ph
a

Total&C&Mineraliza.on&(g&CO23C&kg31&li6er&C)&

400"

Li6er&Treatment&

!
Figure!4)10.!!Mean!cumulative!C!mineralization!over!the!55)day!litter!diversity!laboratory!incubation.!!The!main!
effect!of!litter!treatment!was!significant!(F14,90!=!8.08,!p!<!0.001).!!Same!letter!superscript!denotes!
nonsignificant!differences!according!to!Tukey!post!hoc!tests.!!Error!bars!represent!1!SE.!!

163!

Total&C&Min&(g&CO2/C&kg/1&li2er&C)&&

!
400#
350#
300#
250#
200#
150#
100#
45#

50#

55#

60#

65#

Li2er&C:N&Ra:o&

Total&C&Min&(g&CO2/C&kg/1&li2er&C)&&

!
Figure!4)11.!!Regression!between!litter!C:N!ratio!and!cumulative!C!mineralization!(adjusted!
R2!=!0.131,!p!<!0.001).!
!
!
400#
350#
300#
250#
200#
150#
100#
8.5#

9.5#

10.5#

11.5#

12.5#

13.5#

Li2er&%Lignin&

!
Figure!4)12.!!Regression!between!litter!%lignin!and!cumulative!C!mineralization!(adjusted!
R2!=!0.228,!p!<!0.001).!
!

164!

Total&C&Min&(g&CO2/C&kg/1&li2er&C)&&

400#
350#
300#
250#
200#
150#
100#
11#

13#

15#

17#

19#

21#

Li2er&Lignin:N&Ra:o&

Total&C&Min&(g&CO2/C&kg/1&li2er&C)&&

!
Figure!4)13.!!Regression!between!litter!lignin/N!ratio!and!cumulative!C!mineralization!
(adjusted!R2!=!0.313,!p!<!0.001).!
!
!
400#
350#
300#
250#
200#
150#
100#
0#

1#

2#

3#

4#

Li2er&Species&Diversity&

!
Figure!4)14.!Regression!between!litter!species!diversity!and!cumulative!C!mineralization!
(adjusted!R2!=!0.075,!p!=!0.002).!
!

165!

Net&N&Mineraliza:on&(mg&N&kg/1&soil&day/1)&

55#
45#
35#
25#
15#
5#
-5#

Li2er&Treatment&

!
Figure!4)15.!!Mean!net!N!mineralization!over!the!55)day!litter!diversity!laboratory!
incubation.!!The!main!effect!of!litter!treatment!was!significant!(F15,96!=!845.21,!p!<!0.001).!!
Only!the!no!litter!treatment!was!significantly!different!from!the!other!treatment!
combinations.!!Error!bars!represent!1!SE.!!
!
!
!
!
!
!
!
!
!
!
!

166!

Discussion(
Litter&quality&and&soil&origin&incubation&
!

!The!high!first)order!decomposition!rate!constants!and!total!C)min!consistently!

observed!when!Phragmites!litter!was!incubated!in!the!different!soil!types!(Table!4)1;!
Figure!4)2)!are!likely!explained!by!the!lower!C:N!ratio!of!Phragmites!litter!compared!to!the!
other!three!species!(Table!4)3).!!In!contrast,!Typha!litter!had!the!lowest!rate!constants!and!
total!C)min!among!different!soil!types,!especially!when!incubated!in!Carex!soil.!!
Decomposition!rates!were!much!greater!in!this!laboratory!incubation!(k!ranged!from!
0.0085!d)1!to!0.0282!d)1)!than!in!field!incubations!of!Phragmites!stem!and!leaf!tissue!whose!
decomposition!(k)!ranged!from!0.0015!d)1!to!0.0051!d)1!(Gessner!2000),!likely!due!to!
constant!laboratory!temperatures!and!the!mechanical!breakup!of!litter!as!part!of!the!
methodology.!!First!order!rate!constants!found!for!Phragmites!stems!in!Chapter!3!(0.0018!
to!0.0025!d)1)!were!also!lower!than!in!this!incubation,!perhaps!in!part!for!the!same!reasons!
that!caused!the!lower!rates!in!Gessner!(2000);!in!addition,!only!stems!were!incubated!in!
the!Chapter!3!litter!bag!assay,!and!stems!are!known!to!be!more!recalcitrant!than!leaves.!!
However,!my!decomposition!rates!were!closer!to!Chimney!and!Pietro!(2006)!that!found!a!
range!of!0.0008!d)1!to!0.0568!d)1!for!four!wetlands!plants!incubated!in!a!constructed!
wetland.!!!
The!relatively!slow!decomposition!of!Typha!litter!is!probably!due!to!its!high!C:N!
ratio!and!physical!structure.!!Typha!litter,!as!with!its!living!biomass,!is!dominated!by!
aerenchyma!tissue!(Sale!and!Wetzel!1983)!that!likely!lowers!physical!contact!with!the!soil,!
thus!potentially!reducing!decomposition!rates.!!It!would!be!interesting!to!test!if!the!
167!

physical!structure!of!the!litter!affects!decomposition!because!this!is!an!attribute!of!litter!
not!usually!considered!to!be!an!important!control!on!decomposition!rate.!!This!could!be!
tested!experimentally!by!incubating!Typha&litter,!along!with!other!species!litter!that!varied!
in!aerenchyma!tissue,!in!wetland!water!in!addition!to!in!soil!because!physical!contact!with!
water!would!not!be!restricted!as!it!is!with!soil.!!!
The!effect!of!litter!quality!on!the!decomposition!of!litter!has!been!shown!previously!
in!a!wide!range!of!plant!types!and!ecosystems!(Eviner!2004;!Xu!and!Hirata!2005;!Orwin!et!
al.!2008;!Parton!et!al.!2007).!The!influence!of!litter!C:N!ratio!(quality)!on!total!C)min!rates!
was!apparent!in!the!regression!analysis!(Figure!4)6)!and!further!supports!my!hypothesis!
that!species)specific!litter!quality!influences!decomposition,!though!the!hypothesis!that!
Phragmites!had!the!most!recalcitrant!litter!was!not!supported.!!This!relationship!was!
stronger!in!the!beginning!of!the!incubation!suggesting!that!litter!quality!had!a!stronger!
influence!early!in!its!decomposition,!probably!due!to!more!labile!litter!components!being!
mineralized!first!(Figures!4)6!and!4)7).!!Rovira!and!Vallejo!(2002)!found!that!when!soils!
decompose!the!quality!usually!decreases!throughout!the!time!of!the!incubation,!and!litter!
in!my!incubation!likely!corresponds!to!what!they!termed!“Labile!Pool!I”,!which!was!the!
most!labile.!! !!!!!
Though!litter!quality!had!large!impacts!on!decomposition!rates!in!the!incubation!
experiment,!the!significant!soil!effects!after!rates!where!corrected!for!background!soil!C)
min!shows!the!influence!of!soil!origin!on!decomposition!rates!and!supports!the!hypothesis!
postulated!in!the!introduction!(hypothesis!1).!!This!significant!soil!origin!effect!was!most!
important!for!Phalaris!litter,!which!showed!significant!differences!in!decomposition!rate!
when!incubated!in!its!own!soil,!Phragmites!soil,!and!Carex!or!Typha!soil!(Figure!4)2).!!Soil!

168!

origin!seemed!to!have!the!least!effect!on!Phragmites!litter,!which!did!not!significantly!vary!
across!soil!origins.!!Conversely,!Phragmites!soil!usually!had!the!lowest!total!C)min!
compared!to!other!specific)species!soil!types!(Figure!4)2).!!Because!total!C)min!was!
corrected!for!background!soil!C)min,!this!effect!is!from!an!aspect!of!the!soil!other!than!its!
direct!decomposition.!!In!contrast!to!Phragmites!litter,!Phragmites!soil!had!the!lowest!soil!
C:N!ratio!of!all!the!other!species)specific!soil!(Table!4)3).!!One!reason!for!the!discrepancy!
between!the!quality!of!the!soil!versus!litter!could!be!that!the!litter!used!in!this!incubation!
was!a!mixture!of!leaf!and!stem!tissue,!and!Phragmites!has!extremely!labile!leaf!tissue!which!
likely!decomposes!fast!in!the!field!leaving!the!recalcitrant!stem!tissue!to!develop!into!the!
soil!substrate!(previous!year!leaf!fall!is!not!recognizable!at!the!beginning!of!the!growing!
season,!personal!observation).!!This!low!soil!organic!matter!quality!may!result!in!a!more!K)
selected!soil!microbial!community,!which!may!not!be!able!to!respond!to!the!litter!inputs!as!
quickly!compared!to!the!other!species)specific!soils!(Fontaine!et!al.!2003).!!!
To!the!best!of!my!knowledge,!the!soil!origin!effect!as!described!in!this!study!has!not!
been!shown!before!within!a!similar!experimental!framework!(though!see!Gholz!et!al.!2000!
and!Ayres!et!al.!2009,!for!the!“home)field!advantage”!effect),!especially!with!soil!collected!
under!different!species!in!the!same!wetland!complex,!though!soil!characteristics!have!been!
shown!to!influence!decomposition.!!For!example,!Giardina!et!al.!(2001)!found!that!soil!C!
mineralization!in!forests!dominated!by!either!quaking!aspen!or!lodgepole!pine!were!
significantly!different,!and!the!difference!wasn’t!due!to!soil!texture,!but!could!have!been!
caused!by!the!quality!of!the!organic!matter!inputs.!!Scott!et!al.!(1994)!found!that!while!soil!
texture!(%!sand!content)!alone!had!little!effect!on!litter!C!mineralization,!a!metric!that!
incorporated!both!soil!texture!and!soil!water!pressure!explained!a!significant!amount!of!

169!

the!variation!in!native!soil!C!mineralization.!!Possible!mechanisms!for!the!soil!origin!effect!
found!in!this!incubation!include!interactions!between!the!soil!organic!matter!and!litter!
(priming!effect,!Fontaine!et!al.!2003),!differences!in!soil!microbial!community!(Waldrop!et!
al.!2000),!and!soil!nutrient!availability!(Liu!et!al.!2006).!!!
In!this!incubation,!the!most!likely!mechanism!of!the!soil!origin!effect!was!soil!
nutrient!availability!as!it!explains!the!majority!of!the!patterns!seen!in!the!data.!!First,!
Phragmites!litter!had!the!highest!quality!among!litter!types!and!its!decomposition!was!not!
statistically!significantly!different!among!soil!origins!(Figure!4)2;!not!dependent!on!the!N!
content!or!C:N!ratio!of!the!soil).!!Second,!Phragmites!soil!had!the!lowest!quality!among!soil!
types!and,!besides!Phragmites!litter,!all!other!litter!types!incubated!in!Phragmites!soil!had!
the!least!C)min!compared!to!other!soil!types.!!Third,!Typha!soil!was!the!highest!quality!soil!
among!soil!types!and!consistently!had!the!highest!C)min!for!each!species)specific!litter!
types.!!A!study!by!Liu!et!al.!(2006)!investigated!the!important!soil!chemical!and!physical!
factors!influencing!the!decomposition!of!two!dominant!plant!species!in!China’s!grasslands!
(Allium&bidentatum!and!Stipa&krylovii)!and!found!that!available!soil!nutrients!(N!and!P)!
increased!decomposition!and!that!this!effect!was!greater!for!lower!quality!litter.!!Though!
the!data!support!soil!nutrient!availability!as!the!mechanism!of!the!soil!origin!effect,!it!is!
possible!that!other!factors,!such!as!the!soil!microbial!community,!played!a!role.!!While!
microbial!“home)field!advantage”!has!been!shown!in!the!literature!(Gholz!et!al.!2000,!Ayres!
et!al.!2009),!it!is!unlikely!to!have!influenced!my!results!because!when!a!specific)species!
litter!was!incubated!in!its!“home!soil”!it!never!resulted!in!the!highest!C!mineralization!
(Figure!4)2).!!Future!research!should!isolate!the!causal!factor!for!the!soil!origin!effect!seen!
in!this!incubation.!!

170!

The!most!consistently!negative!N)min!rates!(i.e.,!net!N!immobilization)!occurred!
when!Phalaris,!Typha,!or!Carex!litter!was!incubated!in!Phalaris!or!Carex!soil.!!This!pattern!of!
N!immobilization!can!be!partly!explained!by!the!C:N!ratio!of!the!species)specific!litter.!!It!
has!been!found!that!organic!matter!with!a!C:N!ratio!greater!than!approximately!30:1!to!
35:1!does!not!supply!the!nutrient!demand!of!the!microbial!decomposer!community,!forcing!
the!microbes!to!scavenge!available!N!from!the!soil!and!thus!causing!N!immobilization!
(Brady!and!Weil!2001),!though!Parton!et!al.!(2007)!showed!that!N!immobilization!
associated!with!litter!quality!occurred!when!the!litter!C:N!ratio!was!less!than!40.!!In!this!
incubation,!the!C:N!ratio!of!litter!from!Phragmites!was!~!28,!which!is!below!the!critical!C:N!
ratio!of!35,!and!all!treatment!combinations!that!included!Phragmites!litter!had!positive!N)
min!rates.!!Similarly,!Phalaris!litter!had!a!C:N!ratio!of!~!40!and!since!this!is!close!to!the!
critical!C:N!ratio!of!35,!immobilization!was!less!than!Carex!and!Typha!litter!(both!with!a!
litter!C:N!ratio!>>!than!35:1),!especially!when!Phalaris!litter!was!incubated!with!Typha!soil,!
which!resulted!in!positive!N)min!rates.!!For!all!litter!types!besides!Carex,!litter!incubated!in!
Typha!soil!had!the!highest!N)min!rates,!which!is!likely!due!to!Typha!soil!having!the!lowest!
C:N!ratio!of!all!soils!resulting!in!the!highest!N)min!rates!when!no!litter!was!added.!
The!results!from!this!experiment!suggest!that!dominant!plant!species!from!the!same!
functional!group!can!influence!C!and!N!cycling!by!species)specific!litter!effects,!and!that!
these!influences!can!have!lasting!effects!in!soils!(soil!origin!effects).!!These!results!may!give!
less!justification!for!categorizing!wetland!species,!especially!invasive!species,!into!
generalized!functional!groups!(Boutin!and!Keddy!1993).!!Further!evidence!for!the!lack!of!
usefulness!of!functional!groups!was!found!by!Bremer!et!al.!(2007),!which!found!that!plant!
functional!group!did!not!affect!nirK)type!denitrifier!communities,!though!plant!species!

171!

identity!did.!!However,!plant!function!group!classification!has!been!found!to!be!useful!in!
other!studies!that!have!shown!that!the!diversity!of!plant!functional!groups!helped!to!
resisted!invasion!by!Centaurea&maculosa!(Pokorny!et!al.!2005).!!All!four!wetland!species!
used!in!this!incubation!had!different!litter!and!soil!quality!properties,!although!they!are!all!
highly!clonal,!emergent!wetland!species!that!can!be!found!in!similar!wetland!habitats!and!
could!be!classified!as!clonal!dominants!by!Boutin!and!Keddy!(1993).!!They!do!vary!in!some!
key!wetland!plant!characteristics,!such!as!total!height,!biomass!production!(though!they!
are!all!high!biomass!producing!species),!flowering!phenology,!and!water!depth!tolerance.!!
For!invasive!species!that!have!become!ubiquitous!wetland!plants,!it!might!be!more!
advantageous!to!consider!species!as!unique!components!of!the!plant!community!and!then!
study!their!species)specific!plant!traits,!instead!of!considering!them!members!of!a!specific!
functional!category.!(!!!!!!
!
Litter&diversity&incubation&
Similar!to!the!soil!origin!incubation,!in!the!litter!diversity!incubation!Typha!litter!
had!the!lowest!total!C)min!rates!and!decomposition!rates!(k!constants)!compared!to!the!
other!single!species!litter!addition!(Figure!4)10),!which,!as!before,!is!likely!influenced!by!its!
high!litter!C:N!ratio!and!physical!structure.!!Phalaris!litter!had!a!similarly!high!C:N!ratio!but!
a!higher!total!C)min!and!decomposition!rate!than!Typha!litter.!!The!general!pattern!of!an!
increase!in!decomposition!as!diversity!increased!was!not!as!apparent!as!hypothesized.!!
Total!C)min!showed!a!more!idiosyncratic!pattern!in!which!the!species!added!had!a!greater!
impact!that!just!the!number!of!species.!!For!example,!when!Phragmites!and!Phalaris&litter!
were!incubated!together,!their!combined!effect!was!greater!than!when!either!was!

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incubated!alone!or!any!of!the!other!litter!diversity!treatments.!!Despite!this!idiosyncratic!
pattern,!litter!diversity!still!had!a!significant!effect!on!total!C)min,!albeit!a!weak!one!(Figure!
4)14).!!The!relationship!between!diversity!and!decomposition!has!been!shown!to!be!
positive,!neutral,!or!negative!(Gessner!et!al.!2010)!so!the!lack!of!a!strong!impact!of!litter!
diversity!on!decomposition!is!not!too!surprising.!!!
Litter!quality!had!a!greater!effect!on!decomposition!than!diversity,!specifically!litter!
lignin:N!ratio!(Figure!4)22).!!The!importance!of!lignin!content!on!decomposition,!due!to!its!
recalcitrant!nature,!has!been!shown!in!multiple!litter!decomposition!studies!(Melillo!et!al.!
1982;!Taylor!et!al.!1989;!Berg!2000).!Litter!C:N!ratio!had!less!of!an!effect!compared!to!the!
litter!quality!and!soil!origin!incubation!probably!because!of!the!higher!similarity!between!
species)specific!litter!quality.!!The!difference!between!species)specific!litter!C:N!ratios!used!
in!this!incubation!compared!to!the!litter!C:N!ratios!for!the!litter!quality!and!soil!origin!
incubation!is!explained!by!the!different!stem:leaf!ratios!used!in!these!incubations.!!For!the!
soil!origin!incubation,!a!1:1!stem:leaf!ratio!was!used!for!each!species!for!standardization!
purposes,!but!for!this!incubation!(litter!diversity)!a!3:1!stem:leaf!ratio!was!used!for!
Phragmites!and!Phalaris!and!a!1:1!stem:leaf!ratio!was!used!for!Carex!and!Typha;&these!
ratios!are!closer!to!what!is!seen!in!the!field.!!The!higher!proportion!of!stems!to!leaves!
decreased!the!lability!of!the!overall!mixture!(i.e.,!increased!the!C:N!ratio).!
Net!N!mineralization!rates!were!less!variable!for!this!incubation!than!the!soil!origin!
incubation!as!all!litter!addition!treatments,!regardless!of!species!identity!or!diversity,!
resulted!in!negative!N)min!rates!(Figure!4)15).!!As!explained!above,!the!litter!C:N!ratio!of!
less!than!30!for!Phragmites,!and!near!that!demarcation!line!for!Phalaris,!was!able!to!explain!
the!immobilization!pattern!seen!for!the!different!treatments!in!the!litter!quality!and!soil!

173!

origin!incubation.!!In!this!incubation,!all!of!the!litter!C:N!ratios!were!greater!than!30!due!to!
the!different!stem:leaf!ratios!used!for!Phragmites!and!Phalaris!(3:1!versus!1:1).!!Therefore,!
since!all!of!the!added!litter!mixtures!were!above!the!critical!C:N!ratio!of!35:1!(at!which!
point!microbes!need!to!scavenge!the!soil!for!available!N!to!support!growth)!all!litter!
addition!treatment!levels!resulted!in!N!immobilization!within!the!soil.!!These!results!
demonstrate!that!recalcitrant!litter,!when!added!to!the!soil,!reduces!the!available!N!
concentration!in!the!soil!which!could!feedback!to!plant!fitness.!!This!ability!of!low!quality!C!
(high!C:N!ratio)!to!reduce!the!availability!of!N!is!well!known!and!has!been!successfully!used!
in!restoration!to!decrease!high!nutrient!conditions!that!invasive!species!respond!positively!
to,!to!allow!native!species!to!establish!(Averett!et!al.!2004).!!!!
Though!the!relationship!between!litter!diversity!and!decomposition!was!weaker!
than!hypothesized,!the!effect!of!litter!diversity!was!still!significant.!!Because!of!this!result,!
one!outcome!of!the!formation!of!monospecific!stands!(and!hence!a!single!species!litter!
layer)!could!be!a!reduction!in!overall!decomposition!and!an!increase!in!organic!matter!
buildup.!!In!other!words,!invasive!species!would!decrease!decomposition!rates!when!they!
reduce!species!(litter)!diversity.!!According!to!the!results!of!this!experiment,!the!identity!of!
the!plant!species!that!forms!a!monospecific!stand!could!play!an!important!role!in!
determining!plant!effects!to!C!and!N!cycling.!!For!example,!in!this!experiment,!Typha!litter!
resulted!in!the!lowest!decomposition!rates!and!could!explain!why!Typha!monospecific!
stand!sites!used!in!these!incubations!had!the!highest!soil!%C.!
!
!
!
!
!
!
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!

Chapter(5(
Conclusions(
Humans!have!removed!the!physical!and!biological!barriers!restricting!the!

population!ranges!of!many!species!around!the!world!resulting!in!a!global!exchange!of!
exotic!species!(Richardson!et!al.!2000).!!While!many!species!are!transported!to!new!areas!
on!freight,!in!ballast!water,!or!for!cultivation,!only!a!few!become!established!and!expand!
into!surrounding!areas!(Williamson!and!Fitter!1996).!!Though!relatively!few!in!number,!
invasive!species!can!have!numerous!negative!impacts!on!the!ecology!of!invaded!areas.!!On!
a!global!scale,!invasive!species!are!considered!to!be!the!one!of!the!greatest!causes!of!
biodiversity!loss,!second!only!to!habitat!destruction!(Walker!and!Steffen!1997).!!!
Many!studies!have!shown!that!invasive!species!dramatically!alter!species!
composition!on!a!local!scale!(Zedler!and!Kercher!2004).!!And!while!there!is!still!some!
debate!about!the!impacts!of!invasive!species!on!biodiversity!at!multiple!spatial!scales!(Sax!
and!Gaines!2003),!their!impact!on!C!and!N!cycling!seems!to!be!more!direct.!!For!example,!a!
meta)analysis!of!94!experimental!studies!showed!that!invasive!plant!species!significantly!
increased!root!and!shoot!C!stocks,!primary!production,!litter!decomposition,!and!N!
availability!compared!to!native!plant!communities!(Liao!et!al.!2007).!!
It!is!important!to!understand!the!impacts!of!invasive!plants!in!wetlands!for!
numerous!reasons.!!Because!of!their!placement!on!the!landscape,!wetlands!are!one!of!the!
most!highly!invaded!ecosystems!with!the!resulting!invasion!ranging!from!the!addition!of!a!
new!co)dominant!to!the!complete!replacement!of!the!local!flora!by!a!monospecific!stand!of!
the!introduced!species!(Zedler!and!Kercher!2004).!!Wetlands!are!often!important!
ecosystems!for!the!biogeochemical!cycling!due!to!their!high!productivity,!low!
decomposition,!and!spatiotemporally!variable!redox!status!due!to!fluctuating!water!table!
175!

position!(McClain!et!al!2003;!Reddy!and!DeLaune!2008).!!Therefore,!the!introduction!of!
new!species!can!affect!wetland!function!by!introducing!new!traits,!or!increasing!the!
abundance!of!an!already!existing!trait,!that!influences!decomposition!rates!or!redox!status!
of!the!soil,!such!as!litter!quality!and!radial!oxygen!loss,!respectively!(Figure!1)1).!!Though!
the!negative!aspects!of!plant!invasions!are!hard!to!ignore,!e.g.,!loss!of!biodiversity,!it!is!
possible!that!plant!invasions!in!wetlands!could!be!partially!beneficial,!such!as!increasing!C!
and!N!storage!or!increasing!denitrification!rates.!
The!broad!goal!of!this!dissertation!was!to!investigate!the!ecosystem!consequences!
of!invasive!plant!species!in!temperate!wetlands,!focusing!on!Phragmites&australis,&Phalaris&
arundinacea!and!Typha × glauca&(hereafter,!Phragmites,!Phalaris,!and!Typha,!respectively).!!
These!are!among!the!most!aggressive!wetland!invaders!in!the!Great!Lakes!area!and!

€
understanding!their!impact!on!biogeochemical!cycling!in!wetlands!is!of!great!importance.!!
In!Chapter!2,!I!characterized!the!spatial!variability!in!C!and!N!storage!and!organic!matter!
quality!in!24!wetlands!in!south)central!Michigan!that!support!monospecific!stands!of!these!
invasive!species.!!Additionally,!I!used!laboratory!assays!to!determine!potential!differences!
in!C!and!N!mineralization!within!monospecific!stands!of!Phragmites,&Phalaris,&and!Typha.&&
In!Chapter!3,!I!investigated!the!mechanisms!by!which!Phragmites!influences!C!and!N!
cycling!in!three!wetlands!in!central!Michigan.!!This!was!accomplished!by!manipulating!
Phragmites!litter!and!living!biomass!within!plots!at!each!site!and!then!monitoring!abiotic!
conditions!and!performing!a!number!of!assays,!including!litter!bag!decomposition,!an!in&
situ!N!mineralization!incubation,!and!a!laboratory!denitrification!incubation.!!In!Chapter!4,!
to!understand!the!effects!of!litter!quality,!soil!origin,!and!plant!diversity!on!C!and!N!
mineralization,!I!performed!two!laboratory!incubations!using!litter!and!soil!collected!from!

176!

monospecific!stands!of!the!three!invasive!species,!as!well!as!Carex&lacustris&(hereafter!
Carex),!a!native!sedge.!!Together,!these!approaches!allowed!me!to!test!multiple!hypotheses(
regarding!direct!and!indirect!effects!of!invasive!plants!on!ecosystem!processes!in!wetlands.!
I!hypothesized!that!invasive!species!would!have!higher!NUE!than!native!species,!and!
therefore!wetlands!that!were!more!invaded!would!have!a!higher!site!NUE!compared!to!
those!that!were!less!invaded!(Figure!1)1:!pathway!1).!!While!there!was!some!support!for!
this!hypothesis!(Figure!2)2),!the!exclusion!of!just!one!site!removed!the!significant!
relationship,!thus!little!support!was!found!for!this!hypothesis.!!This!lack!of!a!convincing!
relationship!likely!indicates!that!instead!of!invasive!wetland!species!being!able!to!attain!
high!biomass!production!through!the!efficient!use!of!N,!they!instead!are!able!to!use!
different!N!pools!than!natives!or!respond!more!positively!to!nutrient!enrichment!(Davis!et!
al.!2000).!!!
My!subsequent!hypothesis!that!wetland!C!stocks!would!be!positively!influenced!by!
invasive!species!was!supported,!although!the!hypothesized!mechanism!behind!the!
relationship!was!not!(invasive!species!have!higher!NUE!than!natives;!Figure!1)1:!pathway!
1,10).!!I!found!evidence!that!both!soil!and!ecosystem!C!stocks!increased!due!to!presence!of!
high!biomass!producing!invasive!species!(Figures!2)5!and!2)6)!and!even!though!invasive!
species!did!not!have!an!influence!on!wetland!N!stocks!(Figure!1)1:!pathway!1,4),!there!was!
evidence!that!native!species!had!a!negative!effect!on!both!soil!and!ecosystem!N!stocks.!!This!
could!be!considered!an!indirect!effect!of!invasive!species!because!of!the!negative!effects!
invasive!species!had!on!the!presence!and!diversity!of!native!species!(Figure!2)1).!!As!for!the!
effect!invasive!species!had!on!wetland!C!stocks,!because!there!was!only!weak!evidence!for!
invasive!species!decreasing!litter!quality!(Table!2)3)!and!no!evidence!for!any!effect!on!soil!

177!

C:N!ratios,!it!is!possible!that!wetland!invasive!species!affect!C!stocks!by!some!belowground!
mechanism,!such!as!greater!belowground!biomass!(BGB)!production!or!lower!quality!BGB,!
which!would!be!in!agreement!with!what!Liao!et!al.!(2007)!found!in!a!meta)analysis!
showing!that!invasive!species!increase!root!C!stocks.!
Besides!the!importance!of!considering!the!cumulative!effects!of!invasive!species,!I!
also!hypothesized!there!would!be!differences!among!the!three!most!dominant!invasive!
species!in!their!effects!on!soil!C!and!N!mineralization.!!In!my!wetland!survey,!I!found!
considerable!support!for!this!hypothesis!(Figure!2)8)!and!was!able!to!connect!this!to!the!
quality!of!their!litter!(Figure!1)1:!pathway!3,8,9),!a!plant!trait!known!to!affect!ecosystem!
functioning!(Eviner!and!Chapin!2003;!Eviner!2004).!!Considering!the!results!from!Chapter!
1!(wetland!survey!and!laboratory!incubations)!it!seems!that!invasive!species!are!
influencing!the!C!(and!to!some!extent!N)!stocks!in!inland!Michigan!wetlands,!but!that!the!
most!dominant!invasive!species!in!the!study!region!differ!in!important!plant!traits,!such!as!
litter!quality,!and!hence!the!identity!of!the!invasive!species!is!important!to!understand!the!
full!effect!of!an!invasion.!
In!Chapter!3,!I!showed!how!removal!of!Phragmites!litter!and!living!biomass!had!the!
hypothesized!effects!of!increasing!light!levels!at!the!soil!surface!and!increasing!soil!
temperature!(Figure!1)1:!pathways!2,6!and!3,7;!Figures!3)7!and!3)8).!!The!effect!on!soil!
temperature,!though,!seemed!to!be!dependent!on!the!time!of!year,!as!warmer!months!with!
more!direct!sunlight!increased!soil!temperature!when!biomass!and!litter!was!removed,!but!
when!there!was!less!direct!sunlight!and!daytime!temperatures!were!lower,!biomass!and!
litter!removal!decreased!soil!temperature!(Figure!3)10).!!This!contrasting!effect!is!likely!
due!to!the!litter!layer’s!ability!to!insulate!the!soil!surface.!!Interestingly,!this!increased!soil!

178!

temperature!did!not!affect!rates!of!litter!bag!decomposition!or!in&situ!N!mineralization!
rates!as!I!had!hypothesized!(Figure!1)1:!pathway!2,6,9!and!3,7,6,9).!!As!mentioned!in!
Chapter!3,!the!lack!of!significant!treatment!effect!could!have!been!due!to!the!depth!of!the!
soil!core!used!in!the!N!mineralization!incubation!and!the!cooler!treatment!conditions!found!
in!the!treatment!plots!when!the!litter!bag!assay!was!performed.!!Additionally,!the!absence!
of!any!treatment!effect!on!potential!denitrification!rates!was!probably!caused!by!
nonsignificant!treatment!effects!on!OM!quality!(a!potential!control!on!denitrification!rates)!
since!the!assay!was!done!in!the!laboratory,!free!from!temperature!variation!among!
treatments!found!in!the!field.!!Litter!and!biomass!removal!did!affect!porewater!ion!
concentrations,!specifically!Na+,!Cl),!Ca2+,!and!NO3),!due!to!either!direct!uptake!or!reduced!
evaporative!concentration!by!evapotranspiration!(Figure!1)1:!pathway!5).!!!
Though!not!initially!hypothesized,!all!process!rate!data!(litter!bag!decomposition,!in&
situ!N!mineralization,!and!potential!denitrification)!showed!strong!site!effects.!!These!site!
effects,!which!included!high!potential!denitrification!rates!at!LLP1!and!LLP2!compared!to!
Glasby!(Figure!3)28),!negative!N!mineralization!and!nitrification!rates!at!LLP1!(Figures!3)
19!and!3)20),!and!a!significant!interaction!between!site!and!depth!for!filter!paper!
decomposition!rates!(Figure!3)27),!were!likely!influenced!by!the!very!different!hydrologic!
conditions!among!the!three!sites.!!Glasby!had!constantly!flooded!conditions,!LLP2!had!a!
water!table!that!fluctuated!above!to!below!the!soil!surface,!and!LLP1!had!a!water!table!
usually!below!the!soil!surface.!!These!differences!in!hydrology!created!variation!in!
moisture!conditions!and!soil!redox!status!among!sites.!!The!effects!of!hydrology!seen!in!this!
study!demonstrate!the!overriding!importance!that!water!table!position!can!have!within!
wetland!sites!that!all!support!the!same!species,!Phragmites,!and!this!concords!with!many!
179!

studies!that!show!the!importance!of!hydrology!to!wetland!function!(e.g.,!Hamilton!2002;!
Trebitz!et!al.!2005;!Sierszen!et!al.!2006).!!!!!
In!Chapter!4,!I!showed!the!effects!litter!quality!has!on!decomposition!rates!among!
species!within!the!same!functional!group!(emergent,!clonal!wetland!dominants;!Boutin!and!
Keddy!1993),!as!well!as!the!effects!of!litter!quality!on!N!mineralization!rates!(Figure!1)1:!
pathway!3,8,9).!!I!found!support!for!my!hypothesis!that!the!four!species!used!in!this!assay,!
Phragmites,!Phalaris,!Typha,!and!Carex,!would!differ!in!litter!quality!and!that!litter!C:N!
ratios!would!be!negatively!related!to!C!and!N!mineralization!rates.!!Though!litter!C:N!ratios!
had!a!clear!linear!relationship!with!decomposition!(Figures!4)6!and!4)7),!there!seemed!to!
be!a!threshold!for!litter!quality!effects!on!N!immobilization,!in!which!litter!with!a!C:N!mass!
ratio!greater!than!~!35!to!40!resulted!in!N!immobilization,!while!C:N!ratios!less!than!the!
threshold!resulted!in!net!N!mineralization!(Figures!4)8!and!4)9).!!!
Besides!litter!quality!effects!on!decomposition,!I!found!strong!soil!origin!effects!
(significant!soil!effects!after!litter!decomposition!rates!where!corrected!for!background!soil!
C!mineralization).!!The!soil!origin!effect!is!likely!due!to!soil!nutrient!availability,!but!it!is!
possible!that!other!factors,!such!as!the!soil!microbial!community,!influenced!litter!
decomposition!rates.!!The!different!litter!quality!and!soil!origin!effects!on!C!and!N!
mineralization!for!these!four!plant!species!is!notable!because!these!species!are!in!the!same!
functional!group!and,!therefore,!their!effects!on!ecosystem!processes!can!sometimes!be!
classified!together!(Diaz!and!Cabido!1997;!Craine!et!al.!2002;!McLaren!and!Turkington!
2010).!In!addition,!their!unique!effects!on!decomposition!and!N!availability!could!feed!back!
to!increase!their!fitness!and!offer!a!mechanism!of!individual!invasion!success.!!For!example,!
because!the!decomposition!of!Phragmites!leaf!litter!was!shown!to!result!in!net!N!

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mineralization!(as!opposed!to!N!immobilization),!especially!when!incubated!in!its!own!soil!
(Figure!4)14),!and!since!Phragmites!has!been!shown!to!have!a!greater!response!to!N!
availability!than!some!native!and!exotic!plant!species!(Minchinton!and!Bertness!2003;!
Saltonstall!and!Stevenson!2007),!this!might!result!in!a!positive!feedback!that!could!explain!
its!success.!
There!is!an!apparent!discrepancy!across!experiments!(Chapters!2!and!4)!in!regard!
to!the!quality!of!Phragmites!litter.!!In!Chapter!2,!Phragmites!litter!had!the!highest!C:N!ratio!
compared!to!the!other!study!species!(indicating!low!quality),!while!in!chapter!4,!
Phragmites!litter!added!in!the!litter!quality!and!soil!origin!incubation!had!the!lowest!C:N!
ratio!among!study!species.!!Also,!in!Chapter!4,!for!the!litter!diversity!incubation,!Phragmites!
litter!was!intermediate!between!Chapter!2!and!the!other!incubation!in!Chapter!4.!!As!
discussed!in!the!discussion!section!for!Chapter!4,!the!discrepancy!between!the!C:N!ratios!of!
Phragmites!litter!additions!in!the!two!incubations!originated!from!different!leaf:stem!ratios!
used.!!Because!leaf!tissue!was!much!more!labile,!the!difference!in!leaf:stem!ratio!
significantly!changed!the!overall!litter!quality.!!The!same!general!explanation!can!be!used!
to!explain!the!very!low!quality!of!Phragmites!litter!observed!in!Chapter!2.!!Litter!collected!
in!Chapter!2!was!from!the!established!litter!layer!at!each!site,!and!therefore!most!of!the!
labile!tissue,!such!as!leaf!material,!had!likely!already!decomposed,!leaving!the!recalcitrant!
stem!tissue.!!The!stark!difference!in!lability!between!stem!and!leaf!tissue!of!Phragmites!
could!have!consequences!to!biogeochemical!cycling.!!Phragmites!is!a!late!season!grass!that!
doesn’t!flower!until!late!August!or!September,!after!which!aboveground!tissue!senesces.!!At!
this!time!leaves!detach!and!fall!to!the!soil!surface.!!The!large!input!of!labile!tissue!to!the!soil!
likely!causes!a!pulse!of!C!and!N!mineralization!and!N!availability.!!Because!of!this!behavior!

181!

(late!senescence!and!leaf!shed),!Phragmites!likely!alters!C!and!N!cycling!temporally!
compared!to!earlier!flowering!native!species!that!do!not!have!as!much!labile!leaf!material.!
As!I!hypothesized,!there!was!a!significant!effect!of!litter!diversity!(Figure!1)1:!
pathway!3,8,9)!on!litter!decomposition!rates!(Figure!4)15),!which!could!indicate!that!an!
outcome!of!the!formation!of!monospecific!stands!(and!hence!a!single!species!litter!layer)!
would!be!a!reduction!in!overall!decomposition!rate!and!an!increase!in!organic!matter!
buildup,!i.e.,!invasive!species!decrease!decomposition!rates!when!they!reduce!species!
(litter)!diversity.!!However,!the!effects!of!plant!species!diversity—and!the!corresponding!
diversity!of!litter!inputs—on!decomposition!rates!were!minimal!and!more!dependent!of!
the!identity!of!the!species!than!just!the!number!of!species!incubated.!!For!example,!the!
greatest!C!mineralization!occurred!when!Phalaris!litter!was!incubated!with!Phragmites!
litter,!exceeding!rates!when!either!of!the!two!species!was!incubated!alone,!suggesting!a!
multiplicative!response!(Figure!4)10).!
While!all!of!the!pathways!shown!in!Figure!1)1!were!investigated!to!some!degree!for!
the!research!described!above,!a!more!thorough!investigation!is!needed!for!some!pathways.!!
In!particular,!for!pathways!2,6,9!and!3,7,6,9,!significant!effects!of!both!living!biomass!and!
litter!were!found!for!light!levels!and!soil!temperatures,!but!these!effects!did!not!translate!to!
significant!effects!on!C!and!N!cycling.!!A!longer,!multi)season!litter!bag!assay!should!be!able!
to!determine!if!the!temperature!effects!are!large!enough!to!influence!decomposition!rates.!!!
Additionally,!the!field!study!investigating!litter!and!living!biomass!effects!on!C!and!N!
cycling!(Chapter!4)!was!only!done!in!monospecific!Phragmites!stands.!!Other!dominant!
invasive!species!should!be!included!in!such!investigations!to!determine!species!differences.!!
There!was!evidence!from!the!porewater!equilibrators!used!in!Chapter!4!that!Phragmites!

182!

affected!nitrate!concentrations!in!the!soil!(Figure!1)1:!pathway!5),!but!the!assay!was!only!
conducted!late!in!the!growing!season.!!Nitrate!concentrations!should!be!measured!
throughout!the!growing!season!to!determine!the!full!extent!of!Phragmites!impact!on!nitrate!
availability.!!Lastly,!significant!effects!of!litter!quality,!litter!diversity,!and!soil!origin!(Figure!
1)1:!pathway!3,8,9)!were!found!for!Phragmites,!Phalaris,!Typha,!and!Carex!during!
laboratory!incubations.!!To!understand!the!strength!of!pathway!3,8,9!in!a!natural!setting,!a!
field!experiment!needs!to!be!conducted!with!the!same!basic!experimental!design!as!the!
incubations!in!Chapter!4,!except!instead!of!CO2!production!in!jars,!litter!mass!loss!could!be!
monitored!in!a!reciprocal!transplant!field!experiment.!!!
Taken!together,!the!results!from!this!dissertation!research!show!how!invasive!
species!influence!C!and!N!cycling!in!inland!Michigan!wetlands!through!plant!traits,!such!as!
litter!quality!and!quantity,!biomass!production,!and!direct!N!uptake.!!Most!wetlands!of!the!
southern!Great!Lakes!region!are!either!invaded!or!under!the!threat!of!invasion!by!
aggressive!wetland!invaders!like!Phragmites,!Phalaris,!and/or!Typha,!therefore!studies!like!
those!described!in!this!dissertation!are!important!if!the!ecosystem!consequences!of!
wetland!invasions!are!to!by!fully!understood.!!If!invasive!species!are!increasing!C!stocks!in!
wetlands,!this!could!be!a!positive!outcome!of!wetland!invasion.!!The!research!I!described!
here!also!has!value!for!wetland!managers!facing!challenges!from!invasive!plants.!!Large!
sums!of!money,!often!from!public!funds,!are!spent!to!control!the!invasive!plants!I!studied!
and!restore!native!plant!communities!in!wetlands.!!We!need!a!better!comprehension!of!
their!impacts!on!wetlands,!which!may!not!all!prove!to!be!negative,!in!order!to!focus!control!
efforts!where!they!are!most!needed.!!!

183!

My!results!also!indicate!some!future!research!opportunities.!!First,!while!inland!
wetlands!are!an!important!feature!to!interior!Michigan,!many!invaded!wetlands!occur!
throughout!the!extensive!Great!Lakes!coastal!zones,!thus!the!results!of!Chapter!2!showing!
the!positive!effects!of!invasive!species!on!inland!wetland!C!stocks!should!be!compared!to!a!
similar!study!of!these!coastal!wetlands.!!Second,!the!major!shortcoming!of!the!biomass!and!
litter!manipulation!study!was!the!short)term!nature!of!the!experiment.!!A!five!to!ten!year!
manipulation!study!may!be!able!to!identify!living!biomass!and!litter!effects!on!soil!organic!
matter!quality!and!quantity!that!could!not!be!elucidated!in!the!study!described!in!this!
dissertation.!!Finally,!the!mechanism!behind!the!soil!origin!effect!found!in!Chapter!4!should!
be!investigated,!along!with!expanding!the!litter!quality!incubation!experiment!to!the!field!
to!determine!if!the!same!patterns!found!in!the!laboratory!incubation!can!be!extended!to!a!
natural!setting.!
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APPENDICES!
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185!

Appendix(A(
!

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!

Table!A)1.!Models!of!Biomass!C!Stock.!!Model!in!bold!indicates!the!best)fit!model!
based!on!lowest!AIC!value.(
Model!
AIC!
∆!AIC! wi!
Null!
1493.53! 21.91! 0.00!
Invasive(Dominance(+(Native(Dominance((
1471.62( 0.00( 1.00(
Invasive!Dominance!
1485.43! 13.81! 0.00!
Native!Dominance!
1485.46! 13.84! 0.00!
Table!A)2.!Models!of!Biomass!N!Stock.!!Model!in!bold!indicates!the!best)fit!model!
based!on!lowest!AIC!value.!
Model!
AIC!
∆!AIC! wi!
Null!
615.13! 77.74! 0.00!
Invasive!Biomass!+!Native!Biomass!!
547.48! 10.09! 0.01!
Invasive!Biomass!
572.09! 34.70! 0.00!
Native!Biomass!
625.19! 87.80! 0.00!
Total(Biomass(
537.39( 0.00( 0.99(
Table!A)3.!Models!of!Litter!C!Stock.!!Model!in!bold!indicates!the!best)fit!model!based!on!
lowest!AIC!value.!
Model!
AIC!
∆!AIC! wi!
Null!
1500.44! 13.68! 0.00!
Invasive!Biomass!+!Native!Biomass!
1507.27! 20.51! 0.00!
Phalaris!Biomass!
1501.86! 15.10! 0.00!
Total!Biomass!
1503.87! 17.11! 0.00!
Phalaris!Biomass!+!Biomass!N!+!Biomass!C!+!Biomass!C:N!
1487.77!
1.01! 0.29!
Phalaris!Biomass!+!Biomass!N!+!Biomass!C!!
1490.15!
3.39! 0.09!
Phalaris!Biomass!+!Biomass!N!
1493.43!
6.67! 0.02!
Biomass(N(+(Biomass(C(+(Biomass(C:N(
1486.76( 0.00( 0.48(
Biomass!N!+!Biomass!C:N!
1490.11!
3.35! 0.09!
Biomass!C:N!
1499.51! 12.75! 0.00!
Biomass!N!
1491.94!
5.18! 0.04!

!
!
!
!
!
!
!
!
!
!
!
!

186!

!
!

Table!A)4.!Models!of!Litter!N!Stocks.!!Model!in!bold!indicates!the!best)fit!model!based!on!
lowest!AIC!value.!
Model!
AIC!
∆!AIC! wi!
Null!
737.54!
1.52! 0.28!
Invasive!Biomass!+!Native!Biomass!
757.66! 21.64! 0.00!
Phalaris!Biomass!
745.76!
9.74! 0.00!
Total!Biomass!
747.63! 11.61! 0.00!
Phalaris!Biomass!+!Biomass!N!+!Biomass!C!+!Biomass!C:N!
751.40! 15.38! 0.00!
Phalaris!Biomass!+!Biomass!N!+!Biomass!C!!
747.22! 11.20! 0.00!
Phalaris!Biomass!+!Biomass!N!
744.30!
8.28! 0.01!
Biomass!N!+!Biomass!C!+!Biomass!C:N!
743.52!
7.50! 0.01!
Biomass!N!+!Biomass!C:N!
740.53!
4.51! 0.06!
Biomass!C:N!
743.40!
7.38! 0.02!
Biomass(N(
736.02( 0.00( 0.61(

!
Table!A)5.!Models!of!Litter!C:N!ratio.!!Model!in!bold!indicates!the!best)fit!model!based!on!
lowest!AIC!value.!
Model!
AIC!
∆!AIC! wi!
Null!
926.87! 18.28! 0.00!
Invasive!Dominance!+!Native!Dominance!
909.33!
0.74! 0.31!
Invasive!Dominance!
923.25! 14.66! 0.00!
Invasive!Dominance!+!Biomass!C!+!Biomass!N!+!Biomass!C:N!
912.72!
4.13! 0.06!
Invasive!Dominance!+!Biomass!N!+!Biomass!C:N!
911.54!
2.95! 0.10!
Invasive(Dominance(+(Biomass(N(
908.59( 0.00( 0.45!
Biomass!C!+!Biomass!N!+!Biomass!C:N!
916.61!
8.02! 0.01!
Biomass!N!+!Biomass!C:N!
915.53!
6.94! 0.01!
Biomass!N!
912.55!
3.96! 0.06!
Biomass!C:N!
921.67! 13.08! 0.00!
!
!
!
!

187!

!
Table!A(6.!Models!of!Soil!C!Stock.!!Model!in!bold!indicates!the!best(fit!model!based!on!lowest!AIC!value.!
Model!
AIC!
∆!AIC! wi!
Null!
2105.64! 38.88!
0.00!
Invasive(Biomass(+(Native(Biomass(+(Litter(Mass(+(Litter(C(+(Litter(N(+Litter(C:N( 2066.76(
0.00(
0.68(
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!
2075.76!
9.00!
0.01!
Invasive!Biomass!+!Litter!Mass!
2103.37! 36.61!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+!Litter!C:N!
2069.09!
2.33!
0.21!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!+!Litter!C:N!
2077.23! 10.47!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!
2084.96! 18.20!
0.00!
Native!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+!Litter!C:N!
2070.80!
4.04!
0.09!
Invasive!Biomass!
2103.62! 36.86!
0.00!
Native!Biomass!
2104.12! 37.36!
0.00!
Litter!C!+!Litter!N!
2080.10! 13.34!
0.00!
Litter!N!+!Litter!C:N!
2082.79! 16.03!
0.00!
Litter!Mass!
2105.62! 38.86!
0.00!
Litter!N!
2090.03! 23.27!
0.00!
!
!
!
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!
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!
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!
!
!
!
!
!
188!

Table!A(7.!Models!of!Soil!N!Stocks.!!Model!in!bold!indicates!the!best(fit!model!based!on!lowest!AIC!value.!

!
!
!
!
!
!
!
!
!
!
!
!
!
!
!

Model!
Null!
Invasive!Biomass!+!Native!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+Litter!C:N!
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!
Invasive!Biomass!+!Litter!Mass!
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+!Litter!C:N!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!+!Litter!C:N!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!
Native(Biomass(+(Litter(Mass(+(Litter(C(+(Litter(N(+(Litter(C:N(
Invasive!Biomass!
Native!Biomass!
Litter!C!+!Litter!N!
Litter!N!+!Litter!C:N!
Litter!Mass!
Litter!N!

189!

AIC!
∆!AIC!
wi!
1548.56! 16.12!
0.00!
1536.78!
4.34!
0.08!
1539.19!
6.75!
0.02!
1551.27! 18.83!
0.00!
1537.44!
5.00!
0.06!
1540.97!
8.53!
0.01!
1543.43! 10.99!
0.00!
1532.44(
0.00( 0.72(
1552.70! 20.26!
0.00!
1547.90! 15.46!
0.00!
1537.69!
5.25!
0.05!
1538.09!
5.65!
0.04!
1547.61! 15.17!
0.00!
1541.31!
8.87!
0.01!

Table!A(8.!!Models!of!Soil!C:N.!!Model!in!bold!indicates!the!best(fit!model!based!on!lowest!AIC!value.!

!

Model!
AIC!
∆!AIC!
wi!
Null!
530.87!
3.60!
0.13!
Invasive!Biomass!+!Native!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+Litter!C:N! 573.96!
46.69!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!
558.55!
31.28!
0.00!
Invasive!Biomass!+!Litter!Mass!
556.95!
29.68!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+!Litter!C:N!
565.50!
38.23!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!+!Litter!C:N!
560.75!
33.48!
0.00!
Invasive!Biomass!+!Litter!Mass!+!Litter!N!
554.21!
26.94!
0.00!
Native!Biomass!+!Litter!Mass!+!Litter!C!+!Litter!N!+!Litter!C:N!
561.15!
33.88!
0.00!
Invasive!Biomass!
543.46!
16.19!
0.00!
Native!Biomass!
539.83!
12.56!
0.00!
Litter!C!+!Litter!N!
531.79!
4.52!
0.08!
Litter!N!+!Litter!C:N!
533.65!
6.38!
0.03!
Litter!Mass!
544.51!
17.24!
0.00!
Litter(N(
527.27(
0.00(
0.76(
Table!A(9.!Models!of!Ecosystem!C!Stock.!!Model!in!bold!indicates!the!best(fit!model!based!on!lowest!AIC!value.!

!

Model!
Null!
Invasive(Biomass(+(Native(Biomass((
Invasive!Biomass!
Native!Biomass!

AIC!
∆!AIC!
wi!
2108.37!
6.79!
0.02!
2101.58(
0.00(
0.74(
2104.43!
2.85!
0.18!
2106.85!
5.27!
0.05!

Table!A(10.!Models!of!Ecosystem!N!Stock.!!Model!in!bold!indicates!the!best(fit!model!based!on!lowest!AIC!value.!
Model!
Null!
Invasive!Biomass!+!Native!Biomass!!
Invasive!Biomass!
Native(Biomass(

AIC!
∆!AIC!
wi!
1547.04!
0.60!
0.38!
1550.75!
4.31!
0.06!
1550.91!
4.47!
0.05!
1546.44(
0.00(
0.51(
190!

Table!A(11.!!Best(fit!model!summary!table!for!each!dependent!variable.!
Dependent!!
Biomass!C!Stock!
Biomass!N!Stock!
!
Litter!C!Stock!
Litter!N!Stock!
Litter!C:N!
!
Soil!C!Stock!
Soil!N!Stock!
Soil!C:N!
!
Ecosystem!C!Stock!
Ecosystem!N!Stock!

Model!Structure!
Invasive!Dominance!+!Native!Dominance!!
Total(Biomass(
!
Biomass!N!+!Biomass!C!+!Biomass!C:N!
Biomass!N!
Invasive!Dominance!+(Biomass(N!
!
Invasive(Biomass(+!Native!Biomass!+!Litter(Mass!+!Litter!C!+!Litter!N!+Litter!C:N(
Native(Biomass(+!Litter(Mass!+!Litter!C!+!Litter!N!+!Litter!C:N(
Litter(N(
!
Invasive(Biomass(+!Native!Biomass!(
Native(Biomass(

!
!

191!

wi!
1.00!
0.99!
!
0.48!
0.61!
0.45!
!
0.68!
0.72!
0.76!
!
0.74!
0.51!

Appendix(B(
!
In!each!reference!plot,!the!following!plant!traits!were!estimated!in!the!2008!and!2009!
growing!season:!aboveground!biomass!(AGB)!production,!nitrogen!use!efficiency!(NUE),!
organ!specific!tissue!chemistry,!litter!mass,!litter!depth,!litter!chemistry,!and!plant!height!
(plant!height!data!were!also!collected!in!2010).!!These!measurements!were!taken!for!both!
baseline!data!and!for!the!ability!to!compare!the!three!P.#australis!sites.!!AGB!production!
was!estimated!in!a!randomly!selected!1!m2!subplot!within!each!permanent!plot!by!
harvesting!standing!biomass!at!the!peak!biomass!period.!!Biomass!samples!were!separated!
into!leaves,!stems,!and!inflorescences,!weighed,!and!analyzed!for!%C!and!%N!on!a!Costech!
Elemental!Analyzer.!!Maximum!plant!height!was!measured!once!a!month!during!the!
growing!season.!!NUE!was!calculated!as!plot!and!plant!level!N!productivity!(g!dry!weight!gO
1!N)!(Berendse!and!Aerts!1987;!van!Ruijuen!and!Berendse!2005).!!Litter!depth!was!

recorded!and!litter!was!collected!from!within!the!1!m2!subplot!(629!cm2),!dried!at!65°C!for!
48!hours,!weighed!and!analyzed!for!%C!and!%N.!!!
Along!with!these!measurements,!belowground!biomass!(BGB)!was!measured!in!the!
summer!of!2009.!!BGB!was!estimated!by!coring!to!a!depth!of!30!cm!using!a!PVC!pipe!(10!cm!
diameter).!!Biomass!was!sampled!to!a!30!cm!depth!because!this!is!within!the!depth!range!
of!the!majority!of!BGB!production!for!P.#australis,!though!it!can!grow!deeper!in!drier!
conditions.!!Five!BGB!cores!were!collected!for!each!site,!one!in!each!reference!plot!and!two!
additional!cores!collected!outside!the!treatment!plots!but!within!the!P.#australis!stand.!!Soil!
was!removed,!washed,!and!sieved!(2!mm)!to!separate!roots!and!rhizomes!from!soil.!!Roots!
and!rhizomes!were!then!dried!to!constant!mass!at!80°C,!weighed,!and!analyzed!for!%C!and!
192!

%N.!!Seasonal!variation!in!tissue!chemistry!was!determined!by!sampling!AGB!three!times!
during!the!growing!season.!
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