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IMPACTS OF SOIL ECOSYSTEM DISTURBANCE ON NEMATODE
COMMUNITY STRUCTURE

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Jessica Jean Smith

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6/01 cJCIRC/DateDuopGS—p. 15

IMPACTS OF SOIL ECOSYSTEM DISTURBANCE ON NEMATODE COMMUNITY
STRUCTURE

By

Jessica Jean Smith

A THESIS
Submitted to
Michigan State University

in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Entomology

2004

ABSTRACT

IMPACTS OF SOIL ECOSYSTEM DISTURBANCE ON NEMATODE COMMUNITY
STRUCTURE

By

Jessica Jean Smith

An understanding of the effect of disturbance on ecosystems is needed for
development of a concept of soil quality. Changes in nematode community structure and
nitrogen mineralization are potential indicators of soil quality. The carrot ecosystem was
used for this research. It was postulated that physical, chemical, and biological
disturbances change nematode community structure and nitrogen dynamics affecting
carrot growth. Three Michigan ecosystems; an organic carrot site, woodland, and com-
soybean ﬁeld were evaluated in a descriptive survey of soil characteristics and nematode
community structure. Three soil core disturbance trials (physical, chemical, and
biological), and a microcosm study were used. Soil characteristics and nematode
community structure were ecosystem and disturbance speciﬁc. Addition of an organic
amendment resulted in increases in nitrogen mineralization and population densities of
bacterivores. Physical disturbance caused a decrease in population densities of
fungivores. The general hypothesis for this project was supported by these research

ﬁndings.

Dedication
To Mom, Dad, and Leah
who helped me when I needed help
and encouraged me when I needed encouragement,

this work is gratefully dedicated.

iii

ACKNOWLEDGMENTS

First I wish to thank Dr. George W. Bird for teaching me as an undergraduate
about nematodes and for later accepting me as a graduate student. His time, patience, and
assistance during the time of my graduate work were much appreciated. I would also like
to thank Dr. John Biernbaum, Dr. Jim Miller, and Dr. Sieg Snapp for serving on my
Master of Science Committee and numerous other aspects of my degree program.

Special thanks must go to John Davenport for his time and patience and particularly his
practical engineering skills and to Becky Gore for her time and patience and her
statistical wizardry.

Thank you again to my family who in ways too numerous to list made it possible
for me to complete this degree.

Thanks must also go to my ﬁ'iends and fellow graduate students who always had
the time to listen and talk, even if it had nothing to do with nematodes. Especially Alicia,
Yvonne, Cassandra, Marisol, Kitty, and Dr. Mike Berney. Furthermore, I would like to
thank the Department of Entomology at Michigan State University for providing a
supportive and nurturing environment in which in work.

This Master of Science Degree research was funded by the
USDA/CSREES/RAMP (Carrot RAMP Project). It was also supported in part by an
award from The Rhodes (Gene) Thompson Memorial Fellowship Fund and the Hudson

Graduate Research Grant.

iv

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. vii

LIST OF FIGURES ................................................................................... x

INTRODUCTION .................................................................................... 1

LITERATURE REVIEW ........................................................................... 2
Soil ............................................................................................. 2
Nematodes .................................................................................... 8
Carrots ....................................................................................... 23

CHAPTER 1

SURVEY AND FUNDAMENTAL

DISTURBANCES OF SOIL ECOSYSTEMS .................................................. 33
Introduction ................................................................................. 33
Methods and Materials ..................................................................... 33
Results ....................................................................................... 43
Discussion ................................................................................... 54

CHAPTER 2

IMPACTS OF FUNDAMENTAL DISTURBANCES

ON A MINIMALLY DISTURBED SOIL ...................................................... 62
Introduction ................................................................................. 62
Methods and Materials ..................................................................... 63
Results ....................................................................................... 70
Discussion ................................................................................... 82

CHAPTER 3

IMPACTS OF PHYSICAL DISTURBANCE AND

AN ORGANIC AMENDMENT ON TWO SOILS ............................................ 87
Introduction ................................................................................. 87
Methods and Materials ..................................................................... 87
Results ....................................................................................... 90
Discussion ................................................................................. 1 04

CHAPTER 4

EXPERIMENT WITH MICROCOSMS.. ...................................................................... 108
Introduction ................................................................................ l 08
Methods and Materials ................................................................... 108
Results ...................................................................................... 113
Discussion ................................................................................. 120

THESIS SUMMARY AND CONLUSIONS ................................................. 123

APPENDICES ..................................................................................... 126
APPENDIX A: Record of Deposition of Voucher Specimens and
Voucher Specimen data ................................................................. 127
APPENDIX B: Soil Test Results ...................................................... 133
APPENDIX C: Carrot Data ............................................................ 136
LITERATURE CITED ........................................................................... 139

vi

LIST OF TABLES

Chapter 1: Survey and Fundamental Disturbances of Soil Ecosystems
Methods and Materials

Table 1: Feeding guilds used in this project and the division of recovered taxa into them.
................................................ 42

Results

Table 1: Soil characteristics of survey samples taken from three sites, at two depths; 0-15
cm (Table 1.A), 15-30 cm (Table 1.B). Means followed by the same letter are not
signiﬁcantly different (P = 0.05). The standard deviation appears below each mean in
parentheses. ......................................................................................... 48

Table 2: Population densities of nematodes in each of ﬁve trophic guilds from soil
samples taken from three survey sites, at three depths, Litter layer (Table 2.A), 0-15 cm
(Table 2.B), and 15-30 cm (Table 2.C). Means followed by the same letter are not
signiﬁcantly different (P = 0.05) ................................................................... 49

Table 3: Nematode taxa recovered from three sites and partitioned among ﬁve trophic
guilds. ................................................................................................ 51

Table 4: Population densities of nematodes in each of ﬁve trophic guilds from two
depths of soil cores, 0-15 cm (Table A), 15-30 cm (Table B), and exposed to various
types of ecosystem disturbancesl. Means followed by the same letter are not signiﬁcantly
different (P = 0.05) ................................................................................... 52

Table 5: Vertical distribution (0-15 and 15-30 cm soil depths) of nematode taxa
associated with ﬁve trophic guilds from soil cores exposed to various ecosystem
disturbances ........................................................................................... 53

Chapter 2: Impacts of Fundamental Disturbances on a Minimally Disturbed Soil
Results
Table 1: Population densities of nematodes in each of ﬁve trophic guilds recovered from
soil cores exposed to ﬁve types of ecosystem disturbances. Means followed by the same

letter are not signiﬁcantly different at the P value indicated on the last line of the table.
........................................... 73

 

' Soil cores were mintained in a greenhouse for 21 days.

vii

Table 2: Nematode taxa associated with ﬁve trophic guilds from soil exposed to
ecosystem disturbances.2 .......................................................................... 74

Table 3: Impact of disturbance on total N03" and NH4+ released from soil cores over a

period of 24 days. .................................................................................. 75
Table 4: Amounts of N03' and WK released from soil cores before disturbances were

applied ................................................................................................ 80
Table 5: Fresh weights of carrots associated with six different disturbances ............... 81

Chapter 3: Impacts of Physical Disturbances and on Organic Amendment on Two
Soils

Results
Table 1: Population densities of nematodes in each of ﬁve trophic roles from soil cores
removed from carrot and woodland sites and exposed to various types of ecosystem

disturbances. ......................................................................................... 93

Table 2: Nematode taxa of ﬁve trophic roles associated with soil from two sites that was
exposed to ecosystem disturbances.3 .............................................................. 94

Table 3: Amount of NO3' and NH4+ recovered from two soils before disturbances were
applied ................................................................................................ 95

Table 4: Total NO3' and NI-L;+ recovered from two soils, disturbed in two ways, over a
period of 24 days .................................................................................... 96

Table 5: Fresh weights of carrots associated with two different soils and two
disturbances. .................................................................................... l 03

Chapter 4: Experiment with Microcosms

Table 1: Amount of NO3' and NH4+ recovered from soil cores before organisms were
inoculated ........................................................................................... 1 15

Table 2: Total NO3' and NIL;+ associated with two controls and three microcosms
inoculated with soil organisms ................................................................... 116

Table 3: Fresh weights (g) of carrots associated with two controls and three microcosms
inoculated with soil organisms ................................................................... 119

 

2 Control, disturbed control, physical disturbance, acid disturbance, sucrose disturbance, and alfalfa meal
disturbance.
3 Control, physical disturbance, and alfalfa meal disturbance.

viii

Appendix A

Table l: Voucher Specimen Data for carrot site, Nodding Thistle Farm ................. 128
Table 2.A: Voucher Specimen Data for woodland, Nodding Thistle Farm .............. 129
Table 2.B: Voucher Specimen Data for woodland, Nodding Thistle Farm ............... 130
Table 3: Voucher Specimen Data for corn ﬁeld, Norm Sandbrook’s Farm .............. 131
Table 4: Voucher Specimen Data for Pseudodiplogasteroides compositus ............... 132
Appendix B
Table 1: Carrot Site. Samples from 0-15 cm (1) and 15-30 cm (2) depths ............... 133
Table 2: Woodland Site. Samples from 0-15 cm (1) and 15-30 cm (2) depths .......... 134
Table 3: Corn Field. Samples from 0-15 cm (1) and 15-30 cm (2) depths. .............. 135
Appendix C
Table 1: Carrot data associated with Experiment 2 .......................................... 136
Table 2: Carrot data associated with Experiment 3 .......................................... 137
Table 3: Carrot data associated with Experiment 4 .......................................... 138

ix

LIST OF FIGURES

Chapter 1: Survey and Fundamental Disturbances of Soil Ecosystems

Methods and Materials

 

Figure 1: Map of the sampling grid used at all three sites to collect survey soil samples
and the carrot site to collect intact soil cores. Grid unit lettering and numbering and the
size of the sampling area are shown. The shaded squares represent the 8 survey samples
collected from the carrot site. Different grid units were chosen for each site and the
cores ................................................................................................... 39

Figure 2: Truck mounted hydraulic soil corer used to remove four-inch diameter soil
cores from the carrot site. Images in this thesis are presented in color ...................... 40

Figure 3: Soil cores collected from the carrot site in PVC containers that were then
placed in clay pots, surrounded by pea stone, and distributed on a greenhouse bench.
Images in this thesis are presented in color ...................................................... 41

Chapter 2: Impacts of Fundamental Disturbances on a Minimally Disturbed Soil
Methods and Materials
Figure 1: Soil core apparatus used to push PVC containers into soil for removal of intact
soil cores from the woodland site. A — PVC container in the forest ﬂoor. B — PVC
container being pushed into the soil. C -— PVC container positioned to be pushed into the

soil. Images in this thesis are presented in color ................................................ 67

Figure 2: Arrangement of soil cores strapped to a vertical board and leachate collection
containers placed beneath each PVC tube. Images in this thesis are presented in color.

..................................................... 68
Figure 3: Removal of carrot plants (Figure 3.A) and division of the soil core into quarters
(Figure 33). Images in this thesis are presented in color ..................................... 69
Results

Figure 1: Recovery of NOg' from soil cores amended with alfalfa meal over an
experimental period of 24 days .................................................................... 76

Figure 2: NFL;+ released over an experimental period of 24 days from soil cores amended
with alfalfa meal .................................................................................... 77

Figure 3: Temporal dynamics of soil NO3' (pg) associated with ﬁve microcosm
disturbances. Images in this thesis are presented in color .................................... 78

Figure 4: Temporal dynamics of soil NIL;+ (pg) associated with ﬁve microcosm
disturbances. Images in this thesis are presented in color .................................... 79

Chapter 3: Impacts of Physical Disturbance and an Organic Amendment on Two
Soils

Results

Figure 1: Recovery of NO3' from carrot site soil amended with alfalfa meal over an
experimental period of 24 days .................................................................... 97

Figure 2: Recovery of NIL;+ from carrot site soil amended with alfalfa meal over an
experimental period of 24 days .................................................................... 98

Figure 3: Recovery of NO3' from woodland site soil amended with alfalfa meal over an
experimental period of 24 days .................................................................... 99

Figure 4: Recovery of NI-L;+ from woodland site soil amended with alfalfa meal over an
experimental period of 24 days .................................................................. 100

Figure 5: Temporal dynamics of soil NO3' (pg) associated with ﬁve microcosm
disturbances. Images in this thesis are presented in color ................................... 101

Figure 6: Temporal dynamics of soil NIL;+ (pg) associated with ﬁve microcosm
disturbances. Images in this thesis are presented in color ................................... 102

Chapter 4: Experiment with Microcosms
Methods and Materials
Figure 1: Photomicrographs of the nematode identiﬁed as Pseudodiplogasteroides
compositus (Komer, 1954) showing the esophagus (A), buccal cavity (B), and vulva (C).
Images in this thesis are presented in color ..................................................... 112

Results

Figure 1: Temporal dynamics of soil N03” (pg) associated with ﬁve different
combinations of soil organisms. Images in this thesis are presented in color. . . . . . . . ....1 17

Figure 2: Temporal dynamics of soil NH4+ (pg) associated with ﬁve different
combinations of soil organisms. Images in this thesis are presented in color.............118

xi

INTRODUCTION

In 2003, Michigan ranked second in the United States in number of fresh market
carrots (Daucus carota L.) planted and harvested (USDA 2004). Historically, most
commercial carrot production in Michigan was limited to muck soils. By the 1950’s,
plant parasitic nematodes had become an important limiting factor for this system.
During the next 25 years, soil fumigants were used widely for nematode control in carrot
production. More recently, the overall quality of muck soils used for vegetable
production has declined, and the production has shifted to mineral soil. If Michigan
carrot production is going to maintain its current level of productivity, the proper
precautions need to be taken in the mineral soils to prevent plant parasitic nematodes
from becoming a major problem similar to what took place in muck soils.

An important step for preventing a problem in a system is understanding how that
system works. In a soil ecosystem this can mean knowing how that ecosystem responds
to changes imposed upon it. In this project we studied soils from an area used to grow
carrots organically and a minimally disturbed woodland. The disturbances that can be
applied to a soil ecosystem were reﬁned to three categories, physical, chemical, and
biological, and then applied to these soils. The objective of this study was to determine
the effect of different types of disturbances on the soil ecosystem as displayed by changes
in nematode community structure, nitrogen dynamics, and carrot growth. It was
postulated that fundamental disturbances cause changes in nematode community

structure and nitrogen dynamics that have an effect on carrot growth.

Literature Review

This project encompasses soil ecosystems, tropic roles of nematodes, and the
concept of soil quality. While soil science and the role of plant-parasitic nematodes in
agriculture have long histories, the roles of bacterial and fungal feeding nematodes and
their relationships to soil quality are comparatively recent subjects. Though ancient
cultures recognized the degradation of soil quality (McNeill and Winiwarter 2004),
discoveries about the workings of soil in the late 1800’s changed our concept and use of
soil to a more mechanistic one.

The recognition of soil as a whole interdependent working system has reemerged.
Science is now discovering that aspects which were previously ignored can tell us
important things about the soil ecosystem that we otherwise may not be able to observe
ﬁrst hand. The application of this knowledge will be important for the continuation of
food production on degraded land and to prevent the degradation of more land. These
topics are covered in this Literature Review under the headings of Soil (structure,
ﬁrnction, and soil quality), Nematodes (biology, trophic roles, nematode community
structure, and role in nutrient cycling), and Carrots (biology, production systems, plant-

parasitic nematode associations, and relation of soil quality to carrots).

Soil is an important component of the human environment. It provides the
structure on which we build houses, cities, and roads and maintains our environmental

quality, ﬁlters water as it percolates to the water table, and provides the medium in which

we grow crops for food and ﬁber. The recognition of the importance of soil to human life
has been documented since the beginnings of agriculture. Some of the earliest
documentation from China described the use of green manures to improve soil quality
(Korcak 1992). Agricultural practices grew from this point, focused on the biological
aspect of the soil and how to maintain soil fertility by supporting that biological aspect.
In the 1840’s Justus von Liebig promoted the theory that minerals were all that was
required for plant growth the track of agricultural practices changed. When this
happened most of our previous knowledge of how to maintain soil quality was forgotten
and agriculture became focused on N-P-K. About 100 years later J .I. Rodale began to
promote the idea of “organic agriculture” and the use of those forgotten practices that had
allowed our ancestors to survive for thousands of years on the same land without a
decline in soil quality. Scientists are now working to understand how the physical and
biotic components of the soil interact to maintain soil fertility and as we continues down
this road soil quality will become an important part of soil science.

Structure. Soil has its genesis in bedrock. As bedrock is weathered it is broken
into smaller pieces of matter by the forces of erosion; wind, rain, and ice. This is now the
parent material of soil and through interactions with living organisms and other soil
forming processes, the parent material develops into recognizable soil. This process can
continue for 1,0005 of years until a near steady state is reached which is denoted by the
development of the soil proﬁle (Troeh and Thompson 1993). A soil’s speciﬁc proﬁle is
dependent on the parent material, climate, glacial activity, water deposits, topography,
and the interactions with living organisms. The proﬁle appears as layers referred to as

horizons named O, A, E, B, C, and R. The O horizon is made up of accumulated dead

organic matter that is partly decomposed and has not yet moved into the soil. The A
horizon is where most of the humus that develops will accumulate while the E horizon is
where maximum eluviation, or the removal of solid materials as particles or in solution,
occurs. The B horizon is the zone of maximum illuviation, or deposition of eluviated
particles. Below the B horizon is the C horizon which is sometimes referred to as the
parent material. Finally the bedrock layer is called the R horizon (Troeh and Thompson
1993). All these horizons vary in depth and composition and a soil may even have more
than these six horizons.

Besides horizons, another aspect of soils is soil texture. There are 12 different
soil textures and they are deﬁned by their proportions of the three soil particles, sand, silt,
and clay. These proportions will determine water and nutrient holding capacity of the
soil. Given the percentages of sand, silt, and clay, the texture of a soil can be determined
using the USDA soil texture triangle. The arrangement of the soil particles, and their
mixture with organic matter, then determines the soil structure. The types of soil
structure are: structurless - single grains or massive; structured - granular, platy, blocky
(subangular or angular), or prismatic; and structure destroyed - puddle (Troeh and
Thompson 1993). Another aspect of soil structure is aggregates and their arrangement.
Aggregates are groups of particles that cohere to one another and the strength of this
cohesivness determines the aggregate’s stability. Aggregate stability is how well the
aggregates stay together when exposed to water. If they fall apart when moistened then
the overall structure of the soil will begin to breakdown. Aggregate stability is
determined by soil texture, type of clay, the ions associated with the clay, the kind and

amount of organic matter, and the associated biota (Troeh and Thompson 1993).

Soil organic matter (SOM) has been mentioned previously in relation to soil
structure and nutrient and water holding capacity of the soil. It is the decomposing dead
material ﬁom plants and animals. Other deﬁnitions of SOM also include living plant
roots and soil biota (Troeh and Thompson 1993, Cooperband 2002). Leaves that drop off
plants, the residue left after a crop is harvested, the cells that slough off roots as they
grow through the soil, dead insects, nematodes, and microbes, all contribute to the SOM
portion of a soil. Therefore, the more of each of these organisms that are present on or in
a soil, the more they can contribute to the soil’s organic matter pools. The A horizon of a
soil can contain 1-5 % organic matter (Troeh and Thompson 1993). If a soil contains
enough organic matter that it dominates the soil properties then it is classiﬁed as an
organic soil (Troeh and Thompson 1993). These soils are often formed under a lake or
pond where organic matter collects for years but breaks down very slowly because it is
submerged in water.

Soil organic matter can be divided into three pools based on the length of time it
remains in the soil before it is broken down. These three pools are short-term soil
organic matter, which is present for ca. 1 year; intermediate soil organic matter, which is
present for ca. 3-8 years; and long-term, or recalcitrant, soil organic matter, which is
present in the soil for ca. 1,000-2,000 years (Bird et al., Cavigelli et al. 1998, Sikora and
Stott 1996). Each of these pools contributes in a different way to the characteristics of
soil organic matter. Short—term soil organic matter is an immediate source of plant
nutrients as it is decomposed quickly. In contrast the recalcitrant soil organic matter is

primarily responsible for physical characteristics of soil (Cavigelli 1998). The

intermediate soil organic matter pool is similar to the short-term pool, but the release
nutrients is slower. In total SOM is a dynamic part of the soil.

Function. The whole soil ecosystem has many functions including water ﬁltering
and storage and nutrient cycling. Many nutrients are immobilized in living organisms.
When those organisms die the nutrients are released during decomposition, becoming
available for plant uptake again. Most of this decomposition takes place in the soil and is
carried out by the ubiquitous decomposers, bacteria and fungi.

Decomposition is part of every nutrient cycle, but there is more awareness and
greater understanding about some nutrient cycles than others. For example, the process
of nitrogen cycling has been studied very extensively, due to the fact that it is often the
limiting nutrient in agricultural systems. All living organisms require nitrogen. It is part
of amino acids, and so a part of proteins, and nucleic acids.

The largest reservoir for nitrogen is the lithosphere where 98% of the total
nitrogen on earth is present as a gas (Paul and Clark 1996). For this nitrogen to be used it
needs to be ﬁxed into a form usable by living organisms. Only microorganisms and
microorganisms in association with plants are capable of ﬁxing nitrogen from the
atmosphere and making it available for other organisms in an organic form. The
microorganisms reduce N2 to ammonium then convert it to an organic form. Lightning
strikes are also capable of ﬁxing nitrogen. For consumers to obtain the nitrogen they
need, they must eat and digest plants and other animals.

After nitrogen is ﬁxed it either becomes part of a plant or a bacterium. For other
organisms to get nitrogen they need to consume plants, bacteria, or other organisms that

have eaten plants or bacteria. The nitrogen is now immobilized as long as it is part of an

organism. Then through predation or death and decomposition of that organism, it can
become part of another organism. Another possibility, in the case of animals, is that
excess nitrogen may be excreted by the organism in an inorganic (mineralized) form. If
the organism dies and is decomposed the nitrogen goes through the process of
mineralization or the transformation from an organic form to an inorganic form.
Speciﬁcally, the nitrogen is transformed to NIL;+ (ammonium), a form that many plants
may use as a source of nitrogen. Other bacteria in the soil now use the ammonium and
through the process of nitriﬁcation convert NHX to NO2' (nitrite) and then another set of
bacteria converts N02' to NO3' (nitrate). This process maximally occurs during the
spring and fall as it is affected by aeration, soil moisture (as it affects aeration),
temperature (optimum temperature range is 30-35 ° C), and pH (optimum pH range is
6.6-8.0) (Paul and Clark 1996). To complete the nitrogen cycle, nitrate is the form of
nitrogen used by most plants. Another fate of nitrate and nitrite ions is that they may go
through the process of denitriﬁcation, and by way of N20 and become part of the
atmospheric N2 pool.

Soil Quality. Soil quality has been deﬁned as a measure of the soils’ ability to
hold and release nutrients and water, promote and sustain root growth, maintain suitable
soil biotic habitat, resist degradation, and respond to management. These abilities can be
monitored by examining the soil’s organic matter content, structure, pH, nutrient levels,
and diversity of microbial life including bacteria, fungi, and nematodes to name a few
(Cavigelli et al. 1998). From a farmer’s standpoint, a good quality soil is characterized
by needing few external inputs to produce an ideal yield. It also means that there are few

pathogens in the soil or that their presence has little effect on the crop (Bird 2001).

The ability to quickly and efﬁciently cycle nutrients is certainly part of soil
quality too. As this involves decomposition it is important to support the food web to
keep these processes happening. In a handful of good quality soil there may be millions
of living organisms including bacteria, fungi, amoebae, ﬂagellates, ciliates, nematodes,
insects, oligoceates, mites, etc. All these organisms make up the soil food web. In the
process of obtaining energy they release nutrients as part of the nutrient cycles often
turning an organic form into an inorganic form that can be taken up by a plant and used

for growth.

Nematodes

Nematodes are very numerous and highly varied animals classiﬁed in the animal
Phylum Nematoda. They are aquatic and are present wherever a ﬁhn of water is present,
which is necessary for their movement (Yeates 1998). This includes the oceans,
freshwater bodies, soil, the Antarctic, deserts, the digestive systems of various vertebrates
and invertebrates, and in and on plants. Their numbers have been estimated as enough to
carpet the biosphere with a layer several centimeters thick (Nicholas 1984), or as Nathan
Cobb stated in 1914, “If all the matter in the universe except nematodes were swept
away, our world would still be recognizable . . .” There have been estimates that a hand
full of grassland soil may contain as many as 500 nematodes in each gram of dry soil
(Ingham 2000).

Biology. Nematodes are thread-like in appearance and can range from 0.47 mm
to 8 meters (Gibbons 2002). They are psuedocelomates and are generally referred to as

non-segmented round worms. Nematodes are transparent under light microscopes and

their internal morphology is easy to view. Beginning at the anterior end, a generic
nematode consists of a buccal cavity (mouth), esophagus, intestine, and anal opening.
Females may have one or two, and in some cases more, ovaries and a vagina that may be
located in the middle of the length of the body, towards the posterior end, or in the case
of Xiphenema chambersi, within the ﬁrst 25% of the length of the body. Males may have
one or two testes and a spicule. A structure called the cloaca is the opening for both the
male reproductive system and the anal opening. Males may also have other copulatory
structures such as genital papilla or a bursa, which aid in holding the female during
copulation.

Nematodes have a nervous system, including a nerve ring that is a collection of
ganglia. There are also cephalic papillae arranged around the buccal opening used to
sense the environment. Other sensory structures are the amphids at the anterior end and
phasmids at the posterior end of the nematodes although not all nematodes have
phasmids. These structures are used to sense the environment and may also secrete
substances. There are also nerve cords that run on the dorsal, ventral, and lateral sides of
the body. Nematodes also posses a secretory-excretory system of which the secretory-
excretory pore is the only visible part of this system on the outside of the nematode. The
nematode’s body is covered by a cuticle. The cuticle is also the lining of the openings of
the nematode’s body. The cuticle has three zones in most nematodes, and is covered by
an epicuticle. It is permeable to the surrounding environment of water. The surface coat
consists of carbohydrate and mucin-like proteins, including glycosylation. It is a

dynamic layer with chemical differences among the different life cycle stages (Lee 2002).

Trophic roles. Nematodes can be divided into trophic roles based on their
feeding habits (Yeates et al. 1993). Plant and animal parasites have always been studied
as pathogens. With a recent increased interest in the role of nematodes in soil, groups
have been described based on their food sources and researchers are continuing to divide
the nematodes into these groups. In 1993, Yeates et al. published an article “[presenting]
a consensus of current thought on nematode feeding habits,” of nematodes in plant and
soil systems. Nematodes were divided into eight groups: 1) plant feeder (herbivore), 2)
hyphal feeder (fungivore), 3) bacterial feeder (bacterivore), 4) substrate ingester, 5)
predator of animals (carnivore), 6) unicellular eukaryote feeder (algavore), 7) dispersal or
infective stage of parasites, and 8) omnivore.

Plant feeders are plant parasites and can be subdivided into sedentary, migratory
endoparasites, semiendoparasites, ectoparasites, epidermal cell and root hair feeders,
algal and moss feeders, and feeders on above ground plant tissue (Bongers and Bongers
1998). Hyphal feeders referred to those nematodes that feed on fungi. Bacterial feeders
can also include some infective stages of animal parasites, which feed on bacteria until
they ﬁnd their host. Substrate ingesters include nematodes that ingest a diversity of
matter, but only use speciﬁc types of matter for their metabolism. Animal predation
refers only to nematodes that feed on other nematodes, protozoa, rotifers, etc. Unicellular
eukaryote feeding is a group for nematodes that ingest fungal spores, whole yeast cells, or
algae or diatom cells. Dispersal or infective stages of animal parasites include forms of
animal parasites that may be found in the soil before they enter a host. This includes
vertebrate and invertebrate parasites. The ﬁnal group is the omnivores. Omnivores feed

on a variety of things and since this group may be used as a catch-all it is best to try to

10

place nematodes in other groups ﬁrst so only true omnivores are listed in this group. The
names given to these groupings have been changed by different researchers but they are
essentially the same groups. For example, Freckman and Ettema (1993) used the terms
plant feeders, bacterial feeders, fungal feeders, algal feeders, predators, omnivores, and
insect parasite to partition the nematodes found at the Kellogg Biological Station, Long
Term Ecological Research Site into feeding guilds.

There is general agreement about what the possible trophic roles of nematodes
are, but it is often difﬁcult to classify a particular nematode into a speciﬁc trophic role.
The small size of most nematodes and the inability to observe them in their “natural
environment” has meant that the feeding habits of some need to be inferred by where
they are found or the similarity of buccal cavity and esophagus features to those with
known feeding habits. The majority of plant-parasitic nematodes, for example, have a 3-
part tylenchoid esophagus and a stomatostyle. Some nematodes with tylenchoid esophagi
are fungivores and also have a tylenchoid stylet. Most nematodes that are bacterivores
have a cylindrical buccal cavity with no stomal armature, while carnivores have denticles
and a large mural tooth.

Nematode Community structure. The nematode populations present, their
division into the trophic roles and how those populations interact is referred to as the
nematode community structure. It has been repeatedly demonstrated that nematode
community structure is affected by variables such as plant community, soil moisture,
bacteria, fungi, land management, and chemicals. Relationships have also been noted
between nematode distribution and soil pH and soil texture (Robertson and F reckman

1995).

11

It is largely recognized that plants affect nematode community structure,
particularly the herbivores. Not only do host plants provide a food source for nematodes,
but through incorporation of their residue, root exudates, or partnerships with fungi and
bacteria, plants support the food sources that bacterivores and fungivores feed on (Yeats
1999). Plant parasites are often present in the highest populations around and in the roots
of host plants (MacGuidwin 1989, Huang and Cares 1995). Grifﬁths et al. (1994)
observed the effect of planting barley and applying two types of manure to a Scottish
organic farming system. The planting of a crop increased plant-parasitic nematode
numbers.

Bacterivores and ﬁmgivores are most often found associated with plants or plant
parts. Fungi and bacteria are found in the rhizosphere utilizing the root exudates and
sloughed off cells and around organic matter. It follows then that nematodes that feed on
these organisms will be found in their highest numbers in the rhizosphere and associated
with SOM. Additionally, nematodes have been shown to actively migrate to a food
source, following CO2 and temperature gradients of bacteria and metabolites released by
growing plants (Grifﬁths 1994, Freckman 1988). Ingham et al. (1985) noted a signiﬁcant
difference in the nematode and bacteria interactions occurring in the rhizosphere of Blue
gamma grass and in the nonrhizosphere soil. The conclusion was that “when the
microbial populations of ﬁeld soils are examined without reference to the
rhizosphere/nonrhizosphere separation (as is common practice), important microbial
events mediated by plant roots or nematodes may be diluted and overlooked.” (1985)

Ferris et al. (2004) showed that incorporation of a cover crop in the fall increased

the numbers of bacterivores and fungivores present in that soil the next spring. This

12

effect was varied by the presence of soil moisture. Plots that were irrigated in the fall
were dominated by bacteria while those that were not were fungi dominated. Previous
studies have shown that nematode density is “susceptible to soil moisture dynamics.”
(Gorres et al. 1997) This is because nematodes are aquatic and need a water ﬁlm to
move and their food source needs proper moisture too.

Numerous studies have shown the effects of land management on nematode
community structure. Some of these trials have compared conventional and organic
farming systems. As these systems have two vastly different ways of providing nutrients
for a crop, corresponding differences in nematode community structure might be
expected. Ferris et al. (1996) examined the dynamics of nematode communities in
conventional and organic farming systems cropped with tomatoes. A large increase in
bacterial feeder population density was observed in the organic system at midseason,
though by the end of the season it had decreased again to similar levels with the
conventional system. Probably as a result of the C:N ratio of the crop residues,
fungivores were more abundant in the conventional system and the populations of
herbivores reﬂected cropping sequences (Ferris et al. 1996). Another research project,
which examined the nematode community structure of an organically and conventionally
managed soil, found a higher maturity index in the organically managed soil, but no other
differences (Neher 1999). Maturity index is fully deﬁned later, but it means that the
nematode community consisted of more nematodes that are found in later succession of
an undisturbed ecosystem. F reckman and Ettema (1993) examined nematode populations
in Michigan under four management schemes, high chemical input (conventional tillage

and no-till), organic (low and zero input), successional (abandoned and never tilled), and

13

perennial (poplar and alfalfa). They reported that the relative abundance of plant-
parasites was lowest in the low input organic system. Nematode abundance, however,
was higher in all annual systems compared to the perennial and successional systems.
This brings up the question of the effects of tillage on nematode community structure.

In a project comparing no-till and conventional tillage agroecosystems, the
authors demonstrated that higher densities of bacterivores, fungivores, and total
nematodes were recovered from plots under conventional tillage, while fungivores and
plant-parasites increased in no-till plots during the summer (Parrnelee and Alston 1986).
To further support this the examination of nematode populations in Michigan, described
in the previous paragraph, also displayed higher populations of nematodes in the high
input and organic management systems, where the most tillage was occurring, and more
plant parasites in soil that was being no-tilled (Freckman and Ettema 1993). These
populations were dominated ﬁrst by bacterial feeding nematodes and second by fungal
feeding or plant parasitic nematodes. Pannelee and Alston also showed no changes in the
population densities of omnivores or carnivores. Similarly, Freckman and Ettema did not
ﬁnd any differences in the omnivore populations, but they did ﬁnd differences in the
carnivore populations.

In contrast, a study by Baird and Bernard (1984) found more Heterodera glycines
infective juveniles associated with a conventionally tilled system compared to a no-till
system, the opposite of the two previous studies discussed. Baird and Bernard also found
differences in carnivore populations among no-till and tilled plots. They showed an
increase of carnivores in the no-till plots. It should be noted though that Freckman and

Ettema were comparing cropping systems that had been in place for ﬁve years while

14

Baird and Bernard were using systems that had been established for one year and gave no
description of the cropping history of their site, which could account for the high
population of Heterodera glycines. In fact, Baird and Bernard suggested that a long-term
study might show greater effects and this seems to have been supported by Freckman and
Ettema. Parmelee and Alston (1986) did their research on plots that had been cropped
annually for eight years.

Wardle et al. (1995) combined the land management variables that affect
nematode community structure in a project that compared methods of weed control in an
annual and a perennial cropping system. Organic mulching, cultivation, and herbicides
were evaluated in an annual maize and a perennial asparagus system. The ﬁndings
showed an increase in the bacterial feeding populations in response to cultivation in the
5-10 cm depth of the perennial system. This effect only appeared after the system had
time to “adapt” to the cultivation and increased with time.

Effects of different chemicals have also been noted on nematode community
structure. The chemicals produced by the decomposition of rye grass can repress
populations of root-knot nematode (McSorley and Dickson 1995, McBride et al. 1999).
The effects of creosote on nematodes and decomposition have also been considered.
Blakely et al. (2002) discovered that, “creosote affected soil ecosystems more by altering
soil properties than direct toxicity.” In terms of the nematode community, bacterivores
were common in all contaminated soil examined while the populations of all other
trophic roles decreased. It was not determined, however, if the chemical had any direct
effects on the nematodes although the authors hypothesized that they would since

nematodes have direct contact with the soil.

15

Since a nematode community can react in predictable ways to disturbance,
nematodes should make good indicators of soil quality. In recent years this concept has
gained signiﬁcant momentum and support. Nematodes possess many of the
characteristics desirable in a soil quality indicator. These include: i) their diversity and
participation in many levels of the food web, ii) their presence in every terrestrial
ecosystem, iii) their rapid response to changes in food source, iv) the relative stability of
their populations when undisturbed, v) their ability to survive adverse environmental
extremes, vi) their aquatic nature that allows them to respond to changes in soil water
quantity and quality, vii) their limited ability to move in soil, and viii) the relative ease at
which they can be identiﬁed (Blair et al. 1996).

Many indices have been developed to evaluate nematode community structure.
These can also be used in evaluating soil quality. Tom Bongers developed the Maturity
Index (MI) and the plant-parasite index (PPI) in 1990. The Maturity Index is based on
“c-p” values that are assigned to nematode families. The c-p value is a rating of 1, 2, 3,
4, or 5, 1 being colonizers and 5 being persisters, and is loosely comparable to r and K-
strategists. The characteristics of colonizers include a short life-cycle with a high
reproduction rate, high colonization ability, tolerance to disturbance, and high
ﬂuctuations of population densities. Persisters have a long life-cycle and low
reproduction rate, low colonization ability, are sensitive to disturbance, and their
populations are rather steady. Bongers (1990) used the family level of nematodes taxa
for the MI. It is less time consuming than identiﬁcation to the genus or species level,
making the MI more user friendly. Plant-parasites were treated separately because their

establishment depends on the colonization of plants. As a result there are no l-colonizers

16

as in the MI. Another difference is that the persister plant-parasites occur under stressed
conditions and may even increase. For these reasons, Bongers (1990) also developed the
separate plant-parasite index (PPI). The M1 and PPI may be combined in a ratio for
another level of evaluation.

Ratios are often used to diagnose nematode community structure or the soil food
web. For example, a simple ratio of plant-parasites to non-plant-parasites can indicate if
the soil is suitable for agricultural production. Many other ratios can be used, depending
on the objectives of the researcher. These ratios usually only consider trophic roles and
biological attributes and response to environmental conditions are not included. To
include these last two variables more needs to be known about every nematode genus, or
possibly species, present in a soil food web.

Recently, Ferris, Bongers, and de Goede collaborated to produce the Structural,
Enrichment, and Channel indices, which include trophic roles, biological attributes and
response to environmental conditions (2001). They began by placing nematode genera
into ﬁrnctional guilds based on their trophic role and c-p value. As an example,
Cephalobidae are classiﬁed as Ba2, Ba for bacterivore and 2 for the c-p value. They also
described the possible states of soil food webs as basal, structured, or enriched. A basal
food web has been stressed, the number of species is diminished, and resources are
limited. A structured food web can vary from one that is recovering from a stress and has
more abundant resources and more species to a more mature one with more food web
links and an even greater number of species. Food webs may also be enriched when a
signiﬁcant disturbance occurs and resources become more available. Using a weighted

system and the appropriate equations, the Enrichment Index (E1) and the Structural Index

17

(SI) give a plot position for a food web. The quadrant of the plot that the food web falls
in then gives information about the disturbance, decomposition channel, and C:N ratios
of that food web. They also developed the Channel Index (CI), a weighted ratio of c-p 2
fungivores to c-p 1 bacterivores and c-p 2 fungivores. This index gives an indication of
the dominant pathway of decomposition occurring in the soil food web. In combination,
the E1 and CI “provide a powerful basis for assessing soil fertility levels, nutrient
availability, nutrient leaching potential, and necessary adjustment of C or N to alter these
conditions.” (Ferris et al. 2001)

Role in nutrient cycling. Not only do nematodes make good soil quality
indicators, they are also closely involved in deﬁning the quality of a soil. In terms of
agriculture, a good quality soil is going to support plant growth for an ideal yield and this
implies the ability to cycle nutrients efﬁciently. So the ﬁmctioning of the decomposition
pathways will be very important. Yet, through decomposition, nitrogen may be
immobilized in bacteria and fungi, and unavailable for other organisms such as the crops.
This is where nematodes enter into the nitrogen cycle and play out an important role in
nitrogen cycling. Through the degradation of proteins, amino sugars, and nucleic acid,
nematodes mineralize nitrogen. They degrade proteins, amino sugars, and nucleic acid
when they digest the primary decomposers. The majority of this mineralization of
nitrogen is carried out by the bacterivores and fungivores, although it will be shown that
herbivores also have an effect on the amount of nitrogen mineralized.

Numerous studies have shown that the presence of nematodes increases soil
respiration and the amount of nitrogen mineralized by a given soil ecosystem (Ingham er

al. 1985, Chen and Ferris 2000, Ferris et al. 1998, Trofymow et al. 1983). Ingham et a1.

18

(1985) also showed a positive effect on plant growth in the presence of a bacterium and
nematodes in comparison to other microcosms with only a plant or a plant and the
bacterium. Compared to microfauna, nematodes account for only a small portion of the
total soil respiration, despite their abundance (Yeates 1979). To accomplish this,
nematodes stimulate microfaunal populations leading to more nitrogen mineralization or
even ﬁxation.

There are many ways nematodes can increase the amount of nitrogen mineralized
by a soil system. First, the nematodes themselves are adding to the pool of available
nutrients in the soil. Nematodes have been estimated to have a C:N ratio of 10:1 while
bacteria, on average, are 5:1 (Anderson et al. 1983). This means that when a nematode
feeds on bacteria it is getting more nitrogen than it needs and the excess needs to be
excreted. Nematodes excrete this excess nitrogen in the mineral form of ammonia NIL;+
(Lee and Atkinson 1977, Wright and Newall 1976, Thompson et al. 2002). This is a
form of nitrogen that plants and bacteria are able to directly take up and use for their own
growth.

As stated earlier, another way nematodes increase nutrient mineralization is by
stimulating an increase in the population densities of mineralizers or decomposers. This
may sound counterintuitive as the nematodes are feeding on these organisms, but again
much research has shown that in the presence of nematodes, bacterial population
densities increase. Ingham et al. (1985) compared bacterial populations in soil from
microcosms inoculated with certain known organisms. In this study, all treatments with
nematodes had “signiﬁcantly increased numbers of bacteria, relative to treatments

without nematodes,” and mineralization of nitrogen was also increased. Hunt et a1.

19

(1984) also showed that the presence of grazing nematodes increased bacterial
populations and levels of ammoniﬁcation. Ammoniﬁcation is the conversion of nitrate
and nitrite to ammonia and is carried out by bacteria. However, there have also been
some studies that showed a decrease as opposed to the expected increase, in the bacterial
populations. Anderson et al. (1983) observed such a phenomenon in a microcosm study
similar to Ingham et al. In the Anderson et al. study, the decline in bacterial biomass
was 5 times less than what it should have been to achieve the observed increase in
nematode biomass. This suggests that at times an increase in bacterial biomass may be
consumed before it can be observed. These authors also recorded an increase in nitrogen
mineralization associated with bacterial feeding nematodes.

Increases in nitrogen mineralization have also been observed in relation to the
presence of plant-parasites. In a study conducted with the root-parasitic nematode
Rotylenchulus reniformis, Tu et al. (2003) demonstrated a decrease in microbial biomass
carbon as well as an increase in microbial biomass nitrogen, and higher rates of nitrogen
mineralization. This research was conducted in ﬁeld microplots and undoubtedly
increased the biomass available for consumption by bacterivore nematodes. There was
also a corresponding decrease in cotton yields where the plant-parasite was present.

There are three suggestions for how the grazing of bacteria by nematodes
increases the bacterial population. From 30% to 60% of the bacteria eaten by a nematode
may be defecated alive and thus still capable of growth and reproduction (Smerda et al.
1971, J atala et al. 1974). Secondly, nematodes may transport microbes, either by

adhesion to their cuticle or by being carried in the intestine and defecated alive in another

20

 

location (Freckman 1988). A third possibility is that nematodes may excrete and defecate
products that are rich substrates for bacteria such as amino acids (Anderson et al. 1983).

Fungal feeding nematodes have been shown to increase nitrogen mineralization.
The C :N ratio of fungi is similar to that of the nematode so no excess nitrogen is
consumed. Chen and Ferris, however, showed increased nitrogen in microcosms
containing fungi and ﬁmgal feeding nematodes. This is likely the result of the nematodes
defecating products rich with organic matter that the fungi quickly colonized (Lee and
Atkinson 1977, Wright and Newall 1976). When the results of Tu et al. (1997) are
considered, a fourth mechanism for the increase of nitrogen mineralization is suggested.
Nematode feeding on plant roots enhances leaking of carbon sources and nutrients. This
produces another food source for the decomposers and thus more food for bacterial and
fungal feeding nematodes.

The amount of nitrogen mineralized by the presence of nematodes is affected by
the species of nematode, the composition of the organic matter their food source is
breaking down, and land management. Higher rates of mineralization are usually found
in forests and grasslands where there is generally more organic matter and higher
numbers of nematodes (Grifﬁths 1994). In forested systems, a nematode population may
even be buffered from environmental stress, like lack of water (Gorres et al. 1997).
Ferris et al. (1998) calculated the amount of nitrogen mineralized per individual per day
for eight species of bacterial feeders isolated from a sustainable agriculture research plot
on the campus of the University of California at Davis. The rate was different for each
nematode but an average of these rates was 0.0038 ug-N/nematode/day. Hunt et al.

(1984) estimated that the soil fauna of a Colorado shortgrass prairie was mineralizing

21

2.9g N/mZ/year, a signiﬁcant proportion of the total nitrogen mineralized. In a study with
fungal feeding nematodes, Chen and Ferris (1999) showed an apparent species speciﬁc
effect on the amount of nitrogen mineralized when different fungal feeders and fungus
were analyzed. This is not usually observed with bacterial feeding nematodes.

The composition of organic matter being decomposed affects how much nitrogen
is mineralized. Gould et al. (1981) added different combinations of soil organisms
(bacteria, ﬁmgi, amoebae, and nematodes) to chitin amended soil and observed the
decomposition of chitin and the amount of nitrogen mineralized. While the addition of
nematodes to the bacteria did not increase the decomposition of chitin, it did increase the
mineralization of nitrogen. Treatments with the fungi alone decomposed the most chitin.
The authors concluded that the bacterial population was able to increase using the
decomposition products of the fungus and in turn supported an increase in the nematode
population. This resulted in the observed increase of nitrogen mineralization. When
Grifﬁths et a1. (1994) compared the incorporation of two manures into plots, the
nematode populations reacted differently depending on the manure applied. The ﬁrst,
farm yard manure, had no apparent effect on the nematode population while the second,
poultry manure, increased the nematode population, particularly rhabditoid species. This
difference was attributed to the lower C:N ratio of the poultry manure, which allowed it
to decompose more rapidly. Ferris and Matute (2003) observed a fast rate of succession
from bacterivores to fungivores in microplots receiving materials with a high C :N ratio.
This is clearly another way SOM can affect nitrogen mineralization rates and nematode

community structure.

22

Trofymow et al. (1983) investigated the effects of the simultaneous
decomposition of chitin and cellulose in the presence of a bacterium or a fungus and their
respective grazers. In both the ﬁmgal and the bacterial based systems, the addition of
grazers enhanced nitrogen mineralization. Chitin is usually decomposed faster than
cellulose. This is probably due to its higher nitrogen content. In the Trofymow et al.
project the addition of chitin did not aid in the decomposition of cellulose and usually

decreased its rate of decomposition.

M

Economic Value. Michigan is a major producer of carrots. It ranks second in the
United States in fresh market carrot acres planted and harvested and fourth or ﬁfth in
processing carrots, depending on how much Texas produces (USDA 2004). Last year,
6,100 acres were planted to carrots in Michigan. Of this, 4,400 acres were planted for
fresh market carrots, which yielded 350 chacre. Production was 1,470,000 cwt sold at
$13.10 per cwt, resulting in a total value of $19,257,000. (USDA 2004) This was an
increase compared to 2002, but still within the Michigan average, of the past six years.
The remaining 1,700 acres were planted for processing carrots, with 1,600 acres yielding
24 tons/acre (USDA 2004). The total production of 38,400 tons was sold at $69/ton. The
total value was $2,650,000. This was a slight decrease compared to 2002, but again
staying within the Michigan average. With this much revenue being generated, an
improved understanding of how soil quality affects carrot growth is important for the

future of carrot production in Michigan.

23

Biology. The carrot (Daucus carota L. var. Sativa) is a biennial, dicotyledonous
plant. In the ﬁrst year, most growth goes into the hypocotyl and the taproot, while the
stem remains very short (Havis 1939). During the second year, the ﬂower stalk grows
and produces the characteristic umbel inﬂorescence. Seeds are produced by the end of
the second year.

The carrot taproot is grown for human consumption. This storage organ is most
often recognized in US. markets as having a characteristic orange color, but the color of
this vegetable can vary from white to yellow and can be found with deep shades of red or
purple (Kotecha et al. 1998). This vegetable can also be divided into two types based on
taproot color and leaf appearance. Eastern/Asiatic types are usually reddish-purple or
yellow and the leaves are pubescent appearing gray-green while western types are
orange, yellow, red or white and the leaves are less pubescent appearing to be greener
(Rubatzky et al. 1999). The shape of this vegetable is also variable. Some have stumpy
roots measuring 2-6 cm long and others are cone shaped measuring 6-30 cm in length
(Kotecha et al. 1998).

The color of the carrot root is determined by the pigments it produces and stores.
Two of the major pigments are alpha and beta-carotene, usually in a ratio of 1:2
(Rubatzky and Yamaguchi 1997). These are important precursors to vitamin A and give
carrots their yellow and orange colors. Anthocyanin and lycopene give carrots red to
purplish colored ﬂesh. According to Phan and Hsu ( 1973), the production of carotenes
occurs at the same time of maximum root elongation and expansion, reaching a plateau at
three months. Sugars, mainly sucrose, are also produced and reach a plateau at the same

time (Phan and Hsu 1973).

24

Carrots are a cold weather crop. Temperatures ranging from 15 to 20 ° C
promote growth of “attractive roots” (Kotecha et al. 1998). Higher temperatures result in
shorter and thicker roots and reduce shoot growth. Cooler temperatures encourage a long
slender root (Rubatzky 1997). The optimum temperature for carotene synthesis is 16 to
25 ° C (Rubatzky 1997). Havis (1939) reported that germination and emergence occurred
in 5-6 days at 15-21 ° C. Induction of ﬂowering requires a period of 6 to 8 weeks below
10 ° C (Peirce 1987).

Production systems. As an important part of the Michigan vegetable industry,
carrots are produced for fresh market or processing. Last year, 4,400 acres of the carrots
planted in Michigan were for fresh market and 1,700 acres were planted for processing
carrots (USDA 2004). Carrots are produced on large farms using conventional
technology. They are planted and harvested by machine, rotated with agronomic or other
vegetable crops. Most of these carrots were planted on mineral soils. Historically,
carrots were grown on muck soils in Michigan, but factors such as the establishment of
high population densities of highly pathogenic plant-parasitic nematodes and degradation
of muck have forced an industry shift to mineral soils.

Carrots have a ﬁll] range of diseases and pests that they are susceptible to
including insects, nematodes, bacteria, and fungi. Aster yellows is as foliar disease
caused by a mycoplasma-like organism and is transmitted by the Aster leaﬂropper. Other
insects that cause problems in carrots are the carrot weevil (Listronotus oregonensis),
cutworms (Noctuidae), and green peach aphids (Myzus persicae). Fungal leaf spots
(Alternaria dauci, Cercospora carotae), bacterial blight (Xanthomonas campestris pv.

carotae), Damping off (Pythium spp., Rhizoctom'a solam'), and Powdery mildew

25

(Erysz'phe polygoni) are all foliar diseases and their presence will reduce leaf area and
photosynthesis. Cavity spot (Pythium spp.), Crater rot (Rhizoctonia carotae), root
forking or stubbing (Pythium spp., Phytophthora spp.) are diseases that affect the roots
and will decrease the yield of marketable carrots. The plant-parasitic nematode
associations are described below. Most of these pests and diseases are controlled
chemically and crop rotation with non-hosts. Cultural practices such as a well drained
soil help control some of these diseases.

Plant-parasitic nematode associations. Three plant-parasitic nematodes are
known to be pathogens of carrots in Michigan. These include the Northern root-knot
(Meloidogyne hapla), carrot cyst (Heterodera carotae), and Penetrans root-lesion
(Pratylenchus penetrans) nematodes. These became key pests in muck soils where the
Michigan carrot industry began, and have the potential to spread to mineral soils. Control
is usually obtained with a combination of nematicides, crop rotation, and other cultural
practices. A speciﬁc combination of these factors, however, is needed to control each of
these pests.

From 1986 to 1988 a survey was conducted to determine to what extent Michigan
carrot farms were infested with Northern root-knot and carrot cyst nematodes (Bemey
and Bird 1992). Carrot farms in eight counties were sampled, representing 15% of the
carrot acreage in Michigan. Northern root-knot nematode was found in 69.7% of the
ﬁelds sampled and carrot cyst in 67.4% of the ﬁelds (Bemey and Bird 1992). Also, 80%
of the ﬁelds where northern root-knot was recovered, carrot cyst was also found. The

majority of the sampled ﬁelds were muck soils. Several mineral soil sites had higher

26

populations of root-knot nematodes, compared to the muck soils. The carrot cyst
nematode was not recovered from any of the mineral soil sites (Bemey and Bird 1992).

Although E. A. Bessey published his classic dissertation on root-knot and its
control in 1911, the ﬁrst report of this nematode in Michigan was made by Chitwood in
1953. The Northern root-knot nematode can greatly reduce yields and the quality of
carrots. It is sedentary endoparasitic. Time lapse video has shown the invasion of roots
by newly hatched second stage juveniles (J 23) and their subsequent journey to their ﬁnal
feeding site (Wyss 2002). The J2 enters the root near the meristematic zone. Once inside
the root it migrates between cortical cells to the root tip without causing any cytological
damage (Wyss 2002). Once at the root tip, the J2 turns around, causing some damage to
the meristematic cells. It then continues to travel in the opposite direction, again causing
no damage, until it reaches the zone of root differentiation. Here the nematode induces
the plant to form feeding tubes, giant cells, and root galls. The J 23 become sedentary and
their bodies then begin to enlarge. After molting to the J3, J4, and adult stages, females
start depositing eggs in an egg sac. Root-lmot nematodes reproduce by mitotic
parthenogenesis and consequently are usually all females.

In carrots, the feeding habits of the Northern root-knot nematode cause the
formation of galls, forking and hairy roots where the nematodes enter the root. The shoot
height, root dry weight, and root area are signiﬁcantly affected by the feeding of root-
knot nematode (Slinger 1976). These effects not only reduce the quality of carrots
produced, but also reduce the whole plant’s ability to take up nutrients and grow. The

overall effect is less marketable carrots.

27

Carrot cyst nematode was ﬁrst discovered in the Western Hemisphere in
Michigan, in 1984 by Dr. Ann MacGuidwin (Graney 1985). In Europe, this nematode is
common, but it is found in mineral soils as opposed to Michigan where it is only found in
muck soils, and only in soils used for the production of carrots. Carrot cyst is another
example a sedentary endoparasitic nematode that lives and migrates throughout carrot
roots. Unlike the root-knot nematode, the cyst nematode uses its stylet to puncture root
cells and travel to the vascular cylinder leaving a necrotic trail. Once it reaches the
vascular cylinder, it becomes sedentary and induces the formation of a syncytium, or a
cell with multiple nuclei. Cyst nematodes reproduce primarily by amphimixis. Second-
stage juveniles become sausage shaped and moult to become J 35, 145, and adults. At
maturity, verrniform males exit the root in search of females. Following mating, the
fertilized female retains the eggs in her body, which eventually hardens and become a
protective structure for the eggs.

The presence of carrot cyst nematode causes roots to grow shallowly and
disﬁgured, forming unmarketable carrots. The foliage is stunted and chlorotic and yields
are reduced. Carrot cyst eggs within cysts remain viable in the soil for 10 years without a
host. This implies a need for the use of long-term rotation to help control population
densities. Bemey (1994), however, showed that continuous planting of carrots can
“stabilize populations at levels lower than the highs achieved when plant types change
each year.”

The Penetrans root-lesion nematode is the “most frequently encountered plant-
parasitic nematodes in Michigan,” according to nematologists at Michigan State

University, Diagnostic Services (Warner et al. 2004). This nematode has a very wide

28

host range and is a major pest of tree fruit, small fruit, potatoes and other vegetables in
Michigan. It is a minor pest of many other crops including soybeans, wheat, corn, many
omarnentals, and carrots. Only rarely do population densities become high enough to
cause damage. In one region of Michigan, however, a unique biotype of the Penetrans
root-lesion appears to have developed. This biotype has a greater pathogenicity on
carrots, corn, soybeans, and wheat than other populations existing throughout Michigan.
As mentioned, root-lesion nematodes parasitize many types of plants and are
capable of causing severe damage and yield losses. These nematodes are migratory
endoparasites occurring in soil and in roots of susceptible plants (Bird and Melakeberhan
1993). They enter root tissue and migrate through and parasitize cortical cells. Adult
Pralylenchus spp. are vermiform and free to leave the root and travel through the soil to
another feeding site. Therefore, they can infect plants as second, third, and fourth-stage
juveniles or as adults (Bird and Melakeberhan 1993). Using their stylets to puncture root
tissue cells to feed upon cytoplasm results in a necrotic trail indicating where the
nematode has fed and moved on. Additionally, the successful invasion of a nematode
attracts other nematodes to the same site to enter leading to more damage (Wyss 2002).
Damage from feeding eventually causes the appearance of a lesion or a brown, necrotic
area that can become infected by secondary invaders. Overall, infected plants will
become chlorotic and stunted, but these symptoms are not usually seen until infestation
populations are reached. Female root-lesion nematodes will then mate with males and
begin to lay eggs inside the root tissue and in the surrounding soil. In carrots, early-

season burrowing, movement, and feeding of this nematode leads to necrosis,

29

discoloration, stunting, and overall disﬁguration of the root leading to reduced yields
increased culls.

Nematode Management. The Northern root-knot has a wide host range
including carrots, celery, onions, potatoes, and strawberries. This makes control with
crop rotation difﬁcult, for carrot growers that produce other vegetables such as celery and
onions. The situation is much less severe for carrot growers that produce non-host
agronomic crops such as corn and wheat. A three or four year rotation with nonhost
crops is often required to lower population densities or reduce risk of a nematode
problem. Carrot cyst nematode however, is only parasitic to carrots and can be more
easily avoided through crop rotation. Once present, however, it can survive for as long
ale years without a host.

Historically, the main chemical used for nematode control in carrot production in
Michigan was fall or early spring soil fumigation with 1-3, dichloropropene (Telone II®,
Telone C-17, Telone C-35, Dow) or metham sodium (Vapam®, Zeneca Ag Products).
Treatment with non-ﬁrmigant nematicides such as oxamyl (Vydate®, Dupont) is the most
common nematicide currently in use. Nondiscrimatory control, however, is equally
effective on all nematodes. Other means of nematode control include prevention of the
spread of the pest by cleaning equipment and machinery between ﬁelds, removing culls
or left over plant parts from the ﬁeld that could harbor the nematode, and the use of
nematicidal crops as green manure at plow down.

Use of host plant resistance is another method of control. This may become key
to managing serious nematode infestations as many of the chemical nematicides in use

are being phased out by stricter environmental guidelines (Robertson 1992). Breeding of

30

resistant cultivars of all plant types has been pursued since the 19703. Not only is
resistance a method of control in its own right, it can increase the effectiveness of other
control methods (Vrain and Baker 1980). This technology has been developed for the
most virulent nematode pests and only in certain crops. As of 1992 there were no
effective host plant resistance programs for carrots. However, the development of
resistance in other plant types and continued screening has moved this method of
nematode control forward for carrots.

Genes for resistance of carrot to Meloidogyne hapla, one of the pests in Michigan,
have been identiﬁed (Wang and Goldman 1996). They appear to be two homozygous
recessive genes which makes breeding of carrots with this resistance very difﬁcult to
carry out as it will involve a lot of backcrossing and screening because most carrot
cultivars are hybrids (Hussey and Janssen 2002). More recently, a dominant, simply
inherited gene for resistance to Meloidogynejavanica and Meloidogyne incognito was
identiﬁed in carrots, although “the resistance does exhibit some allelic dosage response.”
(Simon et al. 2000) Resistant lines are currently being developed and evaluated.

Relation of soil quality to carrots. Carrots can beneﬁt from soil quality in the
same ways similar to most other plants; reduction of pathogens and improved fertility.
Many pathogens of carrots are present in soil, but a general increase in soil biota could
help prevent infection simply by providing competition for the pathogenic biota. As with
other crops, nitrogen is often a limiting nutrient and an increased mineralization rate of
nitrogen could help protect against deﬁciencies. Michigan State University Extension

recommends 50 lbs N/acre before planting and again four to six weeks after seedling

31

emergence. An efﬁciently functioning food web could insure nitrogen mineralization
from soil organic matter to provide nitrogen for crop demand.

Since the portion of a carrot plant that is sold is the root, it is important that
nothing interferes with its growth in a way that disﬁgures it. A hard clay pan or plough
layer may do just this. The continued addition of organic matter to the soil will help
maintain soil structure and keep the soil in such a condition that it is favorable for growth

of attractive carrot roots.

32

Chapter 1

SURVEY AND FUNDAMENTAL DISTURBANCES OF SOIL ECOSYSTEMS

Introduction

When studying a soil that has been farmed for many years, it helps to have a
standard for comparison. Soil samples can be very different and be no more than a few
feet apart or they can be quite similar and be miles apart. These differences and
similarities can be the result of the parent material from which they were formed or the
systems by which they have been managed. This experiment began by analyzing soil
samples from an organic garden, a minimally disturbed woodland, and a conventional
farm for soil nutrition and nematode community structure. The objective was to observe
the characteristics of three soil ecosystems that were in close proximity to each other and
likely had similar soil parent material and were exposed to similar soil formation
processes but have been managed differently for the past 20 years. The second
experiment applied disturbances to soil cores from the carrot site. It was postulated that
the disturbances applied would have distinguishing effects on nematode community

Stl'llCtlll’C.

Methods and Materials

Soil samples for this experiment were collected from Nodding Thistle Farm in
Barry County Michigan (Castelton Township, section 10) and the surrounding area. The
soils in this area are of the Marlette-Oshtemo series. These are loamy soils with a 2-6%

slope (Thoen 1990). Nodding Thistle Farm has been certiﬁed organic for 20 years by the

33

Organic Growers of Michigan. Four to ﬁve acres of the farm are used in the rotation of a
vegetable garden and about 27 acres for ﬁeld crops. Soil fertility is maintained at this
farm mainly by the incorporation of crop residue and weeds. Wood ashes are also added.
Occasionally, blood meal, green sand and rock phosphate are added but this is seldom
done and is only applied below the roots of plants as they are planted. Previously this
farm had been a conventional farm growing ﬁeld corn. The speciﬁc site chosen for soil
core collection was used for the production of carrots in the summer of 2002 (later
referred to as “carrots” or “carrot site”). Soil samples were also collected from two
additional sites. An adjacent wooded area (later referred to as “woodland” or “woodland
site”) has not been farmed for at least 40 years and maybe even longer. The forest
community is composed primarily of beech, hickory, and maple. Samples were also
collected from a second farm approximately a quarter of a mile away from Nodding
Thistle Farm, using conventional farming methods to raise corn and soybeans (later
referred to as “corn ﬁeld”). This site has been no-tilled for at least 10 years and
previously was part of a dairy farm and had been receiving organic matter inputs of dairy
and hog manure. This third site was used to produce corn in the summer of 2002. These
sites were chosen to represent a similar soil texture, developed from the same parent
material as the ﬁrst site, but to show the resultant differences in nematode community
structure at the three sites from different management systems.

At each site, a sampling area of l x 10 meters was randomly chosen. The
sampling area was then divided into a grid of 160 units (4 x 40), each measuring 25 x 25
centimeters. Each column of the sampling grid was lettered A-D and each row was

numbered 1-40 (Fig 1). To randomly select grid units for sampling, the letters and

34

numbers were individually selected at random. This process was repeated until eight
unique grid units had been selected at each sampling site. This same process was used to

select 30 grid units for core removal at the carrot site.

Soil Survey

The sampling grid was set up in each of the three areas. Soil samples were
collected from the eight randomly selected grid units. Each was split into three depths;
litter layer, 0-15 cm, and 15-30 cm. Each depth was collected as a separate sample.
Litter included any decaying plant matter on the top of the soil that had not been
incorporated into the soil. These samples were dug by hand with a trowel and placed in
plastic bags, labeled, and put in a cold storage chamber at 4 °C. From each depth, 100
cm3 of soil was processed to extract the nematodes using the modiﬁed sugar ﬂotation-
centrifugation technique (Jenkins, 1964). For each sample, 100 cm3 of soil was
suspended in eight liters of water. The suspension was then poured through a 1.19 mm
(0.0469 in) and a 38 pm (0.0015 in) sieve. The ﬁltrate was centrifuged at 2000 rpm in
100 ml test tubes (International Equipment Co. West Needham Heights, Mass. 1969) in
water for four minutes, and then in a sugar solution (1362 g/3000ml) for two minutes.
Finally, the suspension was poured through the 38 pm screen again and then washed into
a 15 ml test tube (15x85 mm). Litter samples were also processed using this method.
Some of the litter layer samples contained less than 100 cm3 of soil and litter. When
these samples were counted, each trophic role was adjusted to estimate the total
population in 100 cm3. Portions of the 0-15 cm and 15-30 cm samples were also sent to

the MSU Soil and Plant Nutrient Laboratory and analyzed for pH, phosphorus,

35

potassium, calcium, magnesium, organic matter content, cation exchange capacity, and

percentages of sand, silt and clay.

Soil Ecosystem Disturbance Experiment
Soil cores measuring 10 x 30 cm (2360 cm3) were removed from the carrot site,
using a hydraulic soil corer mounted on a truck (Fig 2). Each non-disturbed core was
then immediately inserted into a 4-inch diameter PVC pipe and placed in a cold storage
chamber at 4 °C. At the beginning of the experiment, the soil cores, in PVC containers,
were placed in clay pots and then surrounded with pea-stone (Fig 3). A piece of screen
was placed over the drainage hole of each pot to prevent the soil from being washed out.
They were then randomly assigned treatments and distributed on a greenhouse bench in
numerical order based on their positions in the collection grid. The greenhouse was made
of glass and had an east-west orientation. The treatments included:
0 a control, which was not disturbed in any way except for being weeded;
o a disturbed control, which was removed from the PVC pipe, pushed through a
0.25 in sieve, and then returned to the PVC container;
0 physical disturbance, in which the upper 15 cm of soil were mixed with a spatula
to simulate tillage;
0 chemical disturbance, where 0.0005 moles of acetic acid was applied as a drench
(0.013 ml of acetic acid in 0.5 L of water);
0 and biological disturbance which was the planting of three carrot seeds (var.
Nantes Fancy Carrot, Fedco Seeds). Each experimental unit was later thinned to

one carrot.

36

All treatments were hand-weeded as the weeds emerged and watered as needed. The
greenhouse temperature was maintained between 24-30 °C and was controlled by vents
and exhaust fans. The greenhouse had a fan/pad system but it was not used.

The experiment started on November 27, 2002, for all treatments except the
chemical disturbance. Cores subjected to the chemical disturbance were added to the
experiment on December 17, 2002. After 21 days under greenhouse conditions each soil
core was pushed out of the PVC container and split into 0-15 cm and 15-30 cm depths.
The carrots were carefully removed from each core and the associated rhizosphere soil
collected.

A 100 cm3 sample of each depth was processed for nematodes using the modiﬁed
sugar ﬂotation-centrifugation technique (Jenkins, 1964). The rhizosphere soil was put in
a Baerrnann funnel and the nematodes collected at 24 and 48 hour intervals. All samples
were stored in a cooler at 4 °C until the nematodes were counted and identiﬁed. All
samples were assessed for nematode community structure using direct count microscopy.
Nematodes recovered were classiﬁed according to trophic guilds: bacterivores,
fungivores, herbivores, carnivores, omnivores, and unknowns (Table 1). Unknowns
included cadavers that could not be identiﬁed and live nematodes that were in a position
on the counting plate that obscured key body parts. The unknowns were included in the
total population of the sample. The nematodes were identiﬁed to the lowest taxon
possible, usually superfamily although some were identiﬁed to species. Some nematode
populations were so large that is was necessary to dilute the sample prior to counting. To

do this the sample was diluted to a known volume and then an aliquot was removed and

37

the nematodes counted and identiﬁed. The result was then multiplied to estimate the total
population of each feeding group.

The nematode communities were preserved in FA. 4:1 ﬁxative (Seinhorst 1966)
and deposited in the Entomology Museum, Michigan State University (Appendix A,
Tables 1-4). The samples are identiﬁed by the following code:

Farm collected from Crop Sample id—Depth”. Example: _N_Ilj C: M

Farm collected from: NTF=Nodding Thistle Farm, Farm2=neighboring farm;

Crop: CT=carrot, WD=woodland, CN=corn;

Sample id: letter and numeral indicated grid position;

Depth: 0=litter layer, 6=0-6 in or 0-15 cm, 12=6-12 in or 15-30 cm.

Statistical Analysis. The data from all experiments were subjected to a random
block design analysis of variance. Tukey’s Test was used to identify differences in
treatment means (P 5 0.05). When Tukey’s test could not separate means, the Least

Signiﬁcant Difference Test was used.

38

Figure 1: Map of the sampling grid used at all three sites to collect survey soil samples
and the carrot site to collect intact soil cores. Grid unit lettering and numbering and the
size of the sampling area are shown. The shaded squares represent the 8 survey samples
collected from the carrot site. Different grid units were chosen for each site and the
cores.

ABCD

25x25 cm

(OQNODU‘l-th—I

10m 20

 

25 cm
25 cm

39

Figure 2: Truck-mounted hydraulic soil corer used to remove four-inch diameter soil
cores from the carrot site. Images in this thesis are presented in color.

 

40

Figure 3: Soil cores collected from the carrot site in PVC containers that were then
placed in clay pots, surrounded by pea stone, and distributed on a greenhouse bench.
Images in this thesis are presented in color.

 

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Results
Soil Survey

Soil Characteristics. The textures of the soil samples taken from the carrot site
were clay loam, except for two, which were loam (Appendix B). One of the exceptions
was collected at a 0-15 cm depth and the other at 15-30 cm. The woodland site was
predominantly sandy loam soil. A loam was found in one 0-15 cm depth sample, one
sample was clay loam at both depths, and another was sandy clay loam at both depths.
In the conventional corn ﬁeld site, nearly half the samples were loam. There were also
six sandy clay loam, two clay loam, and one sandy loam samples collected from this site.

A summary of the soil characteristics for the 0-15 cm depth is presented in Table
LA. The average soil pH was 7.8 at the carrot site, 6.5 at the woodland site, and 6.4 in
the corn ﬁeld (P < 0.001). The three sites were signiﬁcantly different in all the nutrients
analyzed for except for potassium. The concentration of phosphorus at the carrot site was
nearly 13 times that of the woodland site and 5 times that of the cornﬁeld; 150, 12, and
29 ppm respectively (P < 0.001). The carrot site also had the highest concentrations of
potassium, calcium, and magnesium (P < 0.001 for all). The woodland site and the corn
ﬁeld had similar concentrations of potassium. While the highest concentrations of
calcium and magnesium were in the carrot site, the corn ﬁeld had the lowest
concentrations, 994 and 204 ppm, respectively. The woodland site was in the middle
with 1831 ppm of calcium and 248 ppm of magnesium. The organic matter content and
the cation exchange capacity were signiﬁcantly different among the sites (both P <
0.001). The woodland site had the highest organic matter content, 5.3% and the

corresponding highest cation exchange capacity, 17.8 me/ 100g, however the cation

43

exchange capacity of the carrot site was similar. The organic matter content of the carrot
site was 4.0%. Finally, the corn ﬁeld was lowest of both categories; an organic matter
content of 2.3 % and a cation exchange capacity of 9.0 me/ 100g.

At the 15 -30 cm depth, all of the measured parameters were lower than the 0-15
cm depth except for the woodland pH, which was higher (Table 1.8). At this depth, pH
was 7.4 at the carrot site, 6.7 at the woodland site, and 6.3 in the cornﬁeld (P < 0.001).
The phosphorus concentration was again the highest at the carrot site (98 ppm), nearly 12
times that of the woodland site (8 ppm) and 5 times that of the corn ﬁeld (P < 0.001).
Potassium at the carrot site (253 ppm) was about 5 times that at the woodland (49 ppm)
but only 3 times that of the corn ﬁeld (78 ppm) (P < 0.001). The carrot site had the
highest calcium concentration and was similar to the woodland while the corn ﬁeld was
signiﬁcantly lower than both. The concentrations of magnesium were signiﬁcantly
different for all three sites (P < 0.001). The carrot site was highest and the corn ﬁeld had
the lowest concentration of magnesium. At this depth too, the woodland site had the
highest percentage of organic matter, 4.5% compared to 3.2% for the carrot site and 1.9%
for the corn ﬁeld (P < 0.001). However, the cation exchange capacity was nearly equal
for the woodland and carrot sites (13.6 and 13.4 me/ 100g respectively). The corn ﬁeld
was signiﬁcantly lower (P < 0.001).

Nematode Community Structure. One of the litter layer samples ﬁ'om the
carrot site was an outlier and the data discarded because it skewed the statistics for the
site. More bacterivores and fungivores were recovered from this one sample than from
all the other samples combined. In the litter layer, the only signiﬁcant difference among

the sites was the number of bacterivores (Table 2.A). The carrot site mean was 7,396

44

nematodes while the woodland site had 34 and the corn ﬁeld 40 (P = 0.030). The
population densities of fungivores were not signiﬁcantly different at the 0.05 level but
were at the 0.10 level (P = 0.082). The mean of fungivores at the carrot site was 2,660
while the other two sites had fewer fungivores (Table 2.A). The remaining three
nematode guilds, herbivores, carnivores, and omnivores, were not signiﬁcantly different
among the three sites (P = 0.391, 0.178, and 0.181, respectively). There were no
representatives of these trophic groups at the carrot site. In the woodland site there were
0 herbivores, 1 carnivore, and 1 omnivore per 100 cm3 of soil. In the corn ﬁeld there
were 1 herbivore and 0 carnivores and omnivores.

The woodland had signiﬁcantly more bacterivores at the 0-15 cm depth than the
carrot site or the corn ﬁeld (Table 2.B). The woodland contained 531 bacterivores, the
carrot site 39 and the corn ﬁeld 81 (P = 0.001). The woodland had the most ﬁmgivores
and the corn ﬁeld had the least, but the carrot site was not signiﬁcantly different ﬁom
either (P = 0.051). The number of herbivores in the woodland (302) and the corn ﬁeld
(249) were not signiﬁcantly different ﬁ'om each other but were signiﬁcantly different
from the carrot site (5) (P = 0.002). The species complexes of the woodland and the corn
ﬁeld were quite different (Table 3). The numbers of carnivores and omnivores were not
signiﬁcantly different among the sites. (P = 0.105 and 0.187, respectively). The total
population of nematodes in the woodland was signiﬁcantly higher than the other two sites
(P < 0.001).

At the 15-30 cm depth there were differences in the population densities of all
feeding groups except bacterivores and carnivores (Table 2.C). The population densities

of bacterivores was not signiﬁcant at the 0.05 level but was at the 0.10 level. The

45

woodland had more bacterivores while the carrot site and the corn ﬁeld had similar
densities (P = 0.058). The population density of fungivores was signiﬁcantly highest in
the woodland compare to the corn ﬁeld, but the carrot site was not different from either
(P = 0.002). The number of herbivores was signiﬁcantly different between the carrot site
(54) and the woodland (168), but the corn ﬁeld was not different from either (80)
(P=0.039). Carnivore populations were not different among the sites (P = 0.928).
Finally, the number of omnivores was signiﬁcantly different between the woodland and
the corn ﬁeld, but the carrot site was similar to both. The woodland contained 11, the
carrot site 4, and the corn ﬁeld 1 (P = 0.023). The total population of nematodes was
signiﬁcantly highest for the woodland compared to the carrot site and the cornﬁeld which
were not different from each other. Table 3 lists the taxa of nematodes found in the three

different survey sites and the trophic guilds they were placed in.

Disturbance Experiment

Nematode Community Structure. The objective of this experiment was to
determine what effect different types of disturbance had on nematode community
structure. Non-disturbed soil cores were removed from the carrot site and used to
evaluate the effects of fundamental disturbance on nematode community structure at two
depths. The disturbances were limited to those that are experienced in agroecosystems.
The soil cores were maintained in a greenhouse for 21 days. In the 0-15 cm depth there
were signiﬁcant differences (P = 0.028) in the densities of fungivores between the
treatments (Table 4.A). The non-disturbed control had the highest population density of

fungivores (239) and the lowest density was found in the disturbed control (56). The

46

biological, chemical and physical disturbances were not distinguishable from either the
non-disturbed control or the disturbed control. However, at the 15-30 cm depth, this
result was reversed and the disturbed control had a signiﬁcantly (P = 0.026) greater
number of fungivores compared to the other treatments (Table 4.B). The non-disturbed
control and the physical disturbances had the lowest densities of fungivores while the
biological and chemical disturbances were similar to both the high and the low
populations. At both depths the bacterivores and fungivores had the highest population
densities compared to the other trophic guilds but the differences in populations of
bacterivores among treatments were not signiﬁcant at either depth. There were also no
signiﬁcant differences in the herbivore or carnivore population densities of the treatments
at either depth. The number of omnivores was signiﬁcantly different between treatments
at the 0-15 cm depth (P = 0.043), however Tukey’s test was unable to separate these
means. The population densities of omnivores were not signiﬁcantly different at the 15-
30 cm depth (Table 4.B). The total population of nematodes was signiﬁcantly higher (P
= 0.015) in the non-disturbed control of the 0-15 cm depth and lowest in the disturbed
control (Table 4.A). The biological, chemical, and physical disturbances were not
distinguishable from either control. There were no signiﬁcant differences in the total
populations at the 15-30 cm depth (Table 4.B). The different taxa recovered from the

two depths of the soil cores and their trophic roles and listed in Table 5.

47

 

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53

Discussion
Soil Survey

Soil Characteristics. The carrot site had the least variation in soil texture of the
three sites studied. Both the woodland and the corn ﬁeld had four soil textures
represented. Overall, four relatively similar soil textures were found among the three
sites, ranging from clay loam (27-42% clay) to sandy loam (12-27% clay). It is
interesting that the carrot site had the most homogeneous soil texture. This could be the
result of tillage with a rototiller, which is the major method used for seed bed preparation
and weed control on this organic farm. The woodland, of course, is never mechanically
disturbed and the corn ﬁeld is part of a conventional farm and has been no-tilled for at
least ten years. Alternatively, the differences in soil texture may be the result of slight
differences in parent material, glaciation pattern, or other soil forming processes. When
comparing the differences in nutrient composition, the two different farming systems may
be responsible for most of the differences observed among the sites. The carrot site is an
area used primarily to grow root crops and organic matter such as weeds and crop residue
are tilled into the soil four or ﬁve times a year. Wood ashes and occasionally manure is
also added to this site. On the conventional farm, corn and soybeans are rotated yearly
and inorganic fertilizers such as anhydrous ammonia are used in addition to herbicides.

At the 0-15 cm depth, the pH of the woodland site and the corn ﬁeld were not
signiﬁcantly different ﬁ'om each other but were different from the carrot site which had a
higher pH. The carrot plot also had signiﬁcantly higher concentrations of phosphorus,
potassium, calcium, and magnesium than the other two sites. Differences in pH and

nutrient levels may be the result of different management systems. When organic matter

54

is incorporated it decomposes and nutrients are returned to the soil. If a large part of the
organic matter is removed for the site the nutrients are not returned as may happen when
crops are harvested and no organic matter is replaced. This decomposition process may
be happening at a slower rate in the woodland and also on the conventional farm where
tillage does not occur. The particularly large concentration of phosphorus at the carrot
site has probably built up ﬁom the continual return of organic matter coupled with a lack
of erosion. Phosphorus binds tightly to clay and is most often removed by erosion,
removing both the soil and its bound phosphorus. The carrot site also showed a higher
amount of clay and this probably increases the soil’s ability to hold phosphorus. The
result is not an overabundance of phosphorus, but is more than would naturally occur
when compared to the woodland site.

When the three sites are compared in the upper 15 cm, the woodland has
signiﬁcantly more organic matter compared to the other two sites. It is not surprising that
the site with the highest organic matter content would also have the highest CEC since
organic matter provides many binding sites for cations. It was also expected that the
woodland site would have the highest organic matter content since it has been
demonstrated that tillage increases the process of organic matter decomposition
(Slobodian et al. 2002). However, the carrot site which is tilled was signiﬁcantly higher
in both organic matter content and CBC than the corn ﬁeld, which is not tilled.
Additionally, the CEC of the carrot site was not different from that of the woodland. This
could be explained by the amounts of organic matter being incorporated at this site in the
form of cover crops in the spring, plant residue in the fall, and weeds that are tilled down.

Also tillage at this site seldom goes deeper than 15 cm. However, it has also been

55

demonstrated that clay may help protect organic matter from decomposition
(Franzluebbers and Arshad 1997). As the carrot site has a higher amount of clay than the
other two sites, it may be responsible for the higher amount of organic matter. The
observations from the 15-30 cm soil depth were similar to those of the 0-15 cm for the
reasons stated above.

Nematode Community Structure. Populations of nematodes at two soil depths
exhibited differences, most likely as a result of different management practices. The
litter layer is a rapidly changing layer and tends to favor the growth of r-strategists which
respond to enrichment (Ferris et al. 2001), such as bacterivores and fungivores, the
trophic roles with the most representatives in this layer at all the sites. The carrot site had
a signiﬁcantly higher population of bacterivores compared to the other sites. The carrot
site also had greater than 10x the mean population of ﬁmgivores, but due to variability
there were no signiﬁcant differences at the 0.05 level but there were at the 0.10 level.
This implies that there was a larger food source available to fungivores at the carrot site,
compared to the other two sites. The green, vegetative organic matter entering the litter
layer at the carrot site has a lower C:N ratio, compared to the other sites, and is quickly
colonized by bacteria and fungi, providing the food source for the nematodes that feed on
them. Tree leaves and corn stalks however have higher C:N ratios and may decompose
more slowly and therefore are unable to support a ﬂush of bacteria and fungi and there
respective grazers. Soybeans produce very little organic matter so a ﬂush of
decomposers could not be supported then either. Also, because the litter layer is quickly
changing, it is not surprising that the trophic roles which contain K-strategists (omnivores

and carnivores) did not have many representatives at this horizon. All the herbivores

56

 

recovered were parasites of root systems, so few herbivores were expected to be
recovered ﬁ'om the litter layer.

In contrast to the litter layer, at the 0-15 cm soil depth, the woodland site
contained the highest populations of r-strategists, bacterivores and fungivores. This was
again probably due to the amount of organic matter available for decomposition. The soil
survey showed that the woodland site had a higher organic matter content at the 0-15 cm
depth resulting in an abundance of bacteria and fungi for nematode grazing/parasitism.
This soil depth also showed an interesting difference in the population densities of
herbivores. Very few herbivores were present at the carrot site, but the woodland and the
corn ﬁeld had signiﬁcantly higher and similar population densities in this trophic role.
The species complexes, however, were very different. The woodland contained ﬁve
genera of herbivores, two of which are common to in non-disturbed sites. This was
representative of what is expected at a more mature site. In the corn ﬁeld, the majority of
herbivores recovered were T ylenchorhynchus nudus, known as the stunt nematode, a
pathogen of corn. The p0pu1ation level seen is undoubtedly the result of a limited crop
rotation. In contrast, all the herbivore taxa present in the carrot site were also found in
the woodland site. Neither the population densities of carnivores or omnivores were
signiﬁcantly different among the three sites. This could be considered unusual, as a non-
disturbed site such as the woodlot would be expected to have more of these K-strategists.

At the 15-30 cm soil depth the woodlot had the highest populations of
bacterivores (0.10 level) and fungivores (0.05 level), corresponding with the higher
organic matter content. At this depth the population density of fungivores in the carrot

site was not signiﬁcantly different from the woodland site. Since the tillage at the carrot

S7

site does not go much deeper than 15 cm, an increase in fungivores is expected, at the 15-
30 cm soil depth, as tillage seems to reduce fungivore population densities (discussed
later). At this depth, the same herbivores were found at the three sites; however the
population in the corn ﬁeld was not distinguishable from the other two sites. The
populations of carnivores were not signiﬁcantly different but the omnivores were. Unlike
the 0-15 cm soil depth, the woodland site contained signiﬁcantly more of these K-
strategists nematodes compared to the other sites. Since the deeper in the soil nematodes
are the less disturbance they are likely to experience, this is likely the reason this

difference in populations of omnivores was realized at this depth.

Soil Ecosystem Disturbance Experiment

Nematode Community Structure. When soil cores were removed from the
carrot site and fundamental disturbances applied, the results were consistent with
literature reports of how different management affects nematode community structure.
The most noticeable changes in nematode community structure seemed to occur when
interruption of food source or disturbance of physical environment were more intense. If
the ﬁve disturbances applied in this experiment are ranked according to intensity of
disturbance, the least intense was the non-disturbed control and the most intense the
disturbed control where the soil was completely mixed and the soil structure destroyed.
The biological and chemical disturbances could be considered to be equal in intensity,
while the physical disturbance appeared to be slightly more intense.

Based on this disturbance ranking, the responses of the ﬁmgivore populations to

the disturbances at the 0-15 cm soil depth are logical. The food source of fungivores is

58

fungi, which grows hyphae through the soil, absorbing nutrients or parasitizing other
organisms. When these hyphae are broken a portion of them may die while another
portion may start to regrow. Although they may survive and start to grow again, the
population does experience an overall decline. Hyphae are broken by a physical
disturbance to their environment. Considering all of this, ﬁnding the signiﬁcantly highest
population of fungivores in the non-disturbed control was not surprising. With increasing
intensity of physical disturbance, less fungivores were found with the least being found in
the disturbed control. This agrees with the ﬁndings of Parmelee and Alston (1986).
Tukey’s test did not separate the means of omnivore populations at the 0-15 cm
depth, but the more liberal least signiﬁcant difference test (LSD) did. The LSD showed
that the biological and chemical treatments had signiﬁcantly more omnivores compared
to the other disturbances. The disturbed control had the least, and the non-disturbed
control and physical treatment were not different from the high or the low population
densities. Using this statistical test, omnivore population densities also responded to
physical disturbance. This response is the opposite of that observed by Parmelee and
Alston (1986) and Freckman and Ettema (1993), who saw no changes in omnivore
populations. Yet, it corresponds with the functional role to which Bongers (1990) and
Ferris et al. (2001) assigned Dorylaimidae to i.e. greater sensitivity to disturbance.
Dorylaimidae is the family contains the majority of the omnivores observed. The
decrease due to physical disturbance could be because their food source was interrupted
or the physical disruption of their environment made it more difﬁcult for them to move
and obtain food or shelter. Dorylarnoid nematodes can be comparatively large. Perhaps

physical disturbance breaks up the water ﬁlms in which they travel, making it more

59

difﬁcult for them to move, or compaction and breakdown of soil structure reduces the
amount of pore space giving them less travel space.

At the 15—30 cm soil depth, population densities of fungivores were again
signiﬁcantly different based on the type and intensity of the disturbance. The only
disturbance that was known to directly affect this depth in the soil core was the disturbed
control. The physical disturbance only went to a 10-15 cm depth. In contrast to the 0-15
cm depth, the highest population of ﬁmgivores was in the disturbed control. Since the
controls of this experiment and the previous survey samples showed higher populations
of fungivores in the 0-15 cm this could mean that most of this soil was placed in the
bottom of the container after being mixed. However, this ﬁmgivore population of the
disturbed control at the 15-30 cm depth does not appear to be very different from the
population at the 0-15 cm depth. Then the question becomes, why were the fungivore
populations lower for the other disturbances at the 15-30 cm depth in comparison to the
disturbed control? Based on the results of the survey this could be attributed to the
presence of less organic matter at this depth. The mixing of the soil core for the disturbed
control could function to redistribute the organic matter. At the same time the more
oxygen maybe introduced into the 15-30 cm depth by this action, increasing the growth
of ﬁingi.

The population densities of carnivores at the 15-30 cm depth were not separated
by Tukey’s test but were once again separated by the LSD. According to the LSD test,
the carnivores seemed to reﬂect the trend that with more physical disturbance there were

less K-strategists. The lowest populations were in the disturbed control, physical

6O

disturbance, and biological disturbance. Again these results correspond with the
functional role to which Bongers (1990) and Ferris et al. (2001) assigned carnivores.

The nematode community structure associated with the chemical disturbance did
not differ from the non-disturbed control. If there indeed was no difference, it is possible
that the rate at which the acetic acid was applied was too low to have an effect. The
biological treatment, the planting of a carrot, also was not different from the non-
disturbed control. After emergence, the root system of a carrot plant can reach its
maximum length in 21 days, however, the taproot has yet to thicken and form (Slinger
1976). The root system, therefore, may not yet be exerting an effect on the environment
except at the micro-rhizosphere level. Perhaps an effect could have been obtained in this

experiment by pregerminating the carrot seeds or by planting a higher population

Conclusions

The soil survey demonstrated the differences in three sites that have been
managed differently for many years. Of the ﬁrndamental disturbances applied in this
experiment (physical, chemical and biological) to soil cores maintained under greenhouse
conditions, only physical disturbance by surface missing or where the structure of the
entire soil core was destroyed, exhibited changes in the population densities of r- and K-

strategists.

61

 

Chapter 2

IMPACTS OF FUNDAMENTAL DISTURBANCES ON A MINIMALLY

DISTURBED SOIL

Introduction

Nematode communities are different under a forest, grassland, or agricultural
setting. The less disturbed woodlands and grasslands contain a climax community
distinguished by the presence of more omnivores, carnivores, and plant-parasites with
higher c-p values (colonizer-persister scale; 1=colonizer, 5=persister) (Freckman and
Ettema 1993). Agricultural systems are disturbed annually and are dominated by
nematodes with lower c-p values (Parmelee and Alston 1986, Freckman and Ettema
1993). Even if soils are similar in every other way, those that are only minimally
disturbed will react differently to disturbance than those that are disturbed annually
(Ferris et al. 2001). Differences in these reactions impact nematode succession such as
that which occurs when a natural ecosystem is opened for agriculture. Nematode
community structure and nitrogen mineralization of a minimally disturbed soil can then
be used to investigate the impacts of various types of disturbance on the nature and
function of soil.

The objective of this experiment was to determine the effects of disturbance on
nematode community structure, nitrogen availability, and carrot growth in a soil that was
not previously conditioned to these types of disturbances. It was postulated that changes

in nitrogen dynamics would reﬂect changes in nematode community structure and carrot

62

growth. The experiment consisted of a non-disturbed control, disturbed control, physical
disturbance, acid disturbance, sucrose disturbance, and alfalfa meal disturbance applied

to a minimally disturbed soil ecosystem.

Methods and Materials

Intact soil cores were removed from a minimally disturbed woodland site, using
PVC pipe containers measuring 5x15 cm (z300 cm3). These containers had a beveled
edge and were pushed into the soil with a fence post pounder placed over a piece of pipe
designed to ﬁt over the PVC pipe containers (Fig 1). The containers were then pulled
and dug out with the relatively non-disturbed soil core inside. Groups of ﬁve cores were
put in plastic bags and stored in a cold storage chamber at 4 °C until the experimental
period was started. A PVC cap was placed on the end of each tube into which a 2x3 mm
screen was inserted to help hold the soil in. The cap contained a hole for collecting
leachate samples for nitrogen analysis.

On February 3, 2004, approximately 24 h before the start of the experimental
period, the soil cores were brought into a greenhouse, at Michigan State University, to
acclimate to greenhouse temperature, 24-30 °C, and to end any period of arrested activity
of the soil biota brought about by cold storage. The greenhouse was made of glass, with
an east-west orientation and temperature was controlled with vents and exhaust fans. The
top of the soil cores appeared much drier than they were when they were collected and 40
ml of distilled water was added to moisten the soil with out running out the bottom of the
core. For the duration of the experiment, February 4 to February 24, 2004, the cores were
kept in the greenhouse. Any weeds that germinated were cut at the soil level while they

were small to avoid the root system from having an impact on the soil core. The shoot

63

system was laid on the top of the soil core so the nutrients would be returned to the soil.
The cores were placed in a randomized complete block design and strapped to a vertical
board that was high enough to allow the placement of a collection container under each
core (Fig 2). The cores were watered as needed with 10 m1 of distilled water. All cores
were watered the day prior to collection of leachate samples as described below.

The experimental design consisted of the following four disturbances plus non-
disturbed and completely disturbed controls. Six replicate soil cores were each disturbed
in one of the following six ways:

0 A control which was left undisturbed, except for the planting of two carrots,

0 a disturbed control that was removed from the PVC container, broken apart,
mixed, and poured back into the container,

0 chemical disturbance with acetic acid applied at a rate of 0.1 mol/L (0.0057 ml of
acetic acid in 20ml of water),

0 chemical disturbance with sucrose dissolved in water and applied at a rate of 0.1
mol/L (0.684 mg of sucrose in 20 m1 of water),

0 physical disturbance in which the upper 10 cm of the soil core were mixed with a
spatula (this depth was chosen to imitate tillage practices),

0 or an organic matter amendment in which 15 cm3 of alfalfa meal (Bradﬁeld
"Gold" 3-1-5) was added to the upper 10 cm of the soil core and mixed in with a
spatula for one minute.

Six additional cores were treated the same as all other cores but, were removed from the
greenhouse after the leaching on the ﬁrst day and returned to the cold storage chamber.

These cores were used to determine the initial nematode community structure. The

64

ecosystem disturbances were applied on day two. On the third day, two carrot seeds (var.
Nantes Fancy Carrot, Fedco Seeds) were planted into each core with as little disturbance
as possible. The soil was gently opened with a spatula, just enough to allow the carrot
seed to be inserted, and then closed again. The carrot seeds were soaked in distilled
water for three days prior to planting. The experiment was run for a total of 24 days.

Leachate samples for nitrogen analysis were collected on days 0, 1, 6, 9, 12, 15,
18, 21, and 24 according to the procedures of Ferris et al., 1998. On each sampling day,
60 ml of distilled water was poured on the top of the cores and collected in a container
placed beneath each core. The cores were allowed to drain until 30-40 ml of leachate
was collected. The leachate was then ﬁltered through #1 Whatrnan ﬁlter paper to remove
soil particles. All samples were frozen until the end of the experiment when they were all
analyzed for N03' and NH.«.+ at the Michigan State University Soil and Plant Nutrient
Laboratory using an ion analyzer (Lachat Instruments).

After 24 days, each soil core was pushed out of its container and the carrot plants
carefully removed and weighed (Fig 3). The carrots were allowed to dry and weighed
again. The cores were vertically split into quarters, approximately 75 cm3 in volume (Fig
3). One quarter was used for nematode community structure analysis. These soil
samples were processed for nematodes using the modiﬁed sugar flotation-centrifugation
technique (Jenkins 1964). For each sample, 50 cm3 of soil was suspended in 8 L of
water. The suspension was then poured through a 1.19 mm (0.0469 in) and a 38 um
(0.0015 in) sieve. The ﬁltrate was centrifuged (2000 rpm) (International Equipment Co.

Needham Heights, Mass. 1969) in water for 4 min, and then in a sugar solution (1362

65

g/3000m1) for 2 min. Finally, the suspension was poured through the 38 um screen again
and then washed into a 10 m1 test tube. These samples were refrigerated until counted.

The samples were assessed for nematode community structure using direct count
microscopy. Nematodes recovered were classiﬁed according to trophic guilds:
bacterivores, fungivores, herbivores, carnivores, omnivores, and unknowns. Unknowns
included cadavers that could not be identiﬁed and live nematodes that were in a position
on the counting plate that obscured key morphological characteristics. Unknowns were
not analyzed but were included in the total population. Nematodes were identiﬁed to the
most speciﬁc taxon possible. Some were identiﬁed to species. The counting plate was
divided into 12 columns. Every other column was counted and the population of each
trophic guild estimated by multiplying by two.

Statistical Analysis. All the data sets were subjected to random block design
analysis of variance. Tukey’s Test was used to identify differences in treatment means (P

S 0.05).

66

Figure 1: Soil core apparatus used to push PVC containers into soil for removal of intact
soil cores from the woodland site. A — PVC container in the forest ﬂoor. B — PVC
container being pushed into the soil. C — PVC container positioned to be pushed into the
soil. Images in this thesis are presented in color.

 

67

Figure 2: Arrangement of soil cores strapped to a vertical board and leachate collection
containers placed beneath each PVC tube. Images in this thesis are presented in color.

 

68

Figure 3: Removal of carrot plants (Figure 3.A) and division of the soil core into quarters
(Figure 3B). Images in this thesis are presented in color.

A. Soil core and carrots aﬁer carrots were careﬁilly dug out.

  

B. Division of soil for use in analysis.
. . 4 “

69

Results
Nematode Community Structure

The total nematode population density associated with the alfalfa meal
disturbance was signiﬁcantly (P = 0.016) greater than that of the controls or other
disturbances (Table 1). The controls and other disturbances had similar total population
densities. Population densities of bacterivores were signiﬁcantly higher (P = 0.014) in
the presence of alfalfa meal than in any of the other systems. All the other disturbances
had similar population densities of bacterial-feeding nematodes.

The effects of disturbances on herbivores were more variable (P = 0.031). The
lowest herbivore population density was 12 nematodes/ 50 cm3 of soil in the sucrose
disturbance. The highest herbivore population was found in the alfalfa meal disturbance
and was 48/50 cm3 of soil. The alfalfa meal disturbance was similar to all other controls
and disturbances except the sucrose disturbance. The sucrose disturbance resulted in a
signiﬁcantly lower population density of herbivores, however, all other controls and
disturbances, except alfalfa meal, were not distinguishable from it either.

Population densities of omnivores were also signiﬁcantly different among the
disturbances (P = 0.001). The alfalfa meal disturbance possessed the lowest population
density of omnivores (3) while the initial density had the highest (18) (Table 1). All
other disturbancess were similar to one another and not distinguishable from the alfalfa
meal disturbance or initial density. The fungivore and carnivore population densities
were not different among the disturbances and controls. Table 2 presents the taxa of

nematodes recovered from the soil and their trophic roles.

70

may

The disturbances applied to the soil cores affected the amount (pg) of nitrogen
leached as NO3’ and NHX. The total amount of NO3' released in the presence of alfalfa
meal was signiﬁcantly (P < 0.001) higher compared to the control and other disturbances
(Tables 3). The controls and other disturbances were similar to one another. The NO3'
released by the alfalfa meal disturbance also increased signiﬁcantly (P < 0.001) over the
period of the experiment (Fig 1). The total amount of NIH released was signiﬁcantly
increased (P < 0.001) by the alfalfa meal disturbance (Table 3). The NH4+ recovered
from the alfalfa meal disturbance increased signiﬁcantly (P < 0.001) over the
experimental period (Fi g 2). It is important to note that all the disturbances and controls
were not signiﬁcantly different on the ﬁrst day for either the amount of NO3' (P = 0.220)
or NH4Jr (P = 1.000) recovered (Table 4). Figures 3 and 4 display the amounts of NO3'
and NIL;+ released by each disturbance on each leaching day and the trends they formed

over the experimental period.

9am

Germination of the two carrot seeds planted into each core in this experiment
varied from zero to two seedlings. To evaluate the effect of the disturbances on carrot
growth, total carrot weights were reported for each core. Where two carrots were
growing their weights were added together and reported as a single weight. There were
signiﬁcant differences (P = 0.001) among the fresh weights of the carrots reported for
each disturbance (Table 5). The alfalfa meal disturbance had the lowest fresh weight

(0.02] g) while the physical disturbance had the highest fresh weight (0.334 g). The

71

sucrose disturbance was similar to the alfalfa meal disturbance and the non-disturbed
control to the physical disturbance (Table 5). The disturbed control and acid disturbance
were not distinguishable from the other disturbances. Carrot data is included in

Appendix C, Table 1.

72

Table 1: Population densities of nematodes in each of ﬁve trophic roles recovered from
soil cores exposed to ﬁve types of ecosystem disturbances. Means followed by the same
letter are not signiﬁcantly different at the P value indicated on the last line of the table.

 

Nematodes / 50 cm3 of soil

 

Disturbances Bacterivores Fungivores Herbivores Camivores Omnivores Total

 

 

Initial Density 24 b 47 34 ab 4 18 a 145 ab
N°“'D‘St“’bed 22 b 39 19 ab 5 9 abc 108 b
Control
“5““de 52 ab 56 24 ab 4 10 abc 174 ab
Control
Phys“! 18 b 48 21 ab 5 16 ab 121 b
Disturbance
Acid
Disturbance 59 ab 77 19 ab 1 4 bc 190 ab
Sucrose
Disturbance 32 ab 48 12 b 1 6 be 115 b
Alfalfa Meal
Disturbance 117 a 134 48 a 0 3 c 365 3
ANOVA 0.014 0.314 0.031 0.178 0.001 0.016
P Value

 

73

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74

Table 3: Impact of disturbance on total NO3' and NH4+ recovered from soil cores over a

 

 

period of 24 days.
Disturbance NO3' (pg) NH4+(pg)
N°“'d‘s‘“'b°d 0.522 b 0.003 b
control
D'Sm'bed 0.646 b 0.004 b
Control
Physical
Disturbance 0.559 b 0.004 b
Acid
Disturbance 0.553 b 0.003 b
Sugar
Disturbance 0206 b 0.004 b
Alfalfa Meal
Disturbance 2.091 a 0.211 a
ANOVA
P Value < 0.001 < 0.001

 

75

 

Figure 1: Recovery of NOg' ﬁ'om soil cores amended with alfalfa meal over an
experimental period of 24 days.

 

"03' (m9)

 

NO;

 

 

0.01 —- -- hf -

 

0.009 4

 

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0.007 ~

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— Predicted Values

 

 

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0.004 -
0.003 4
0.002 .

 

0.001

Y = 0.000181 x, Q = 0.724, p-value < 0.001

JJI—- —- ————«I -

 

 

IDay

 

 

76

 

Figure 2: NH4+ released over an experimental period of 24 days from soil cores amended
with alfalfa meal.

 

 

 

 

 

 

 

 

 

 

 

 

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Table 4: Amounts of NO3' and NH4+ released from soil cores before disturbances were

 

 

 

applied.

Disturbance NO3’ (pg) N114+ (pg)
Initial Density 1.420 0.009
Non-Disturbed 1.530 0005

Control
Disturbed Control 1.693 0.011
Physical Disturbance 1.392 0.01 1
Acid Disturbance 1.828 0.007
Sucrose Disturbance 1.020 0.008
3:233:21“: 1.367 0.008
21:12:11: 0.220 1.000

 

80

Table 5: Fresh weights of carrots associated with six different disturbances.

 

Carrot Fresh

 

 

Disturbance Weight (g)
Non-Disturbed 0.309 ab
Control
Disturbed
Control 0.202 abc
Physical
Disturbance 0334 a
Acid
Disturbance 02” abc
Sucrose 0 092 bc
Disturbance °
Alfalfa Meal
Disturbance (mu 6
AN OVA
P Value 0001

 

81

 

 

Discussion
Nematode Community Structure

The alfalfa meal disturbance was associated with an increase in the population
density of bacterivores, compared to the initial population density, non-disturbed control,
and physical disturbance, possibly due to an increase in the grazable food source
available to the nematodes, namely bacteria and is the same result described by Ferris et
al. (1996, 2004). The addition of the organic amendment appears to provide a food
source for bacteria. The increase in this population allowed an increase in the population
of bacterivores. A high population of fungivores was also associated with the alfalfa
meal disturbance, but was not signiﬁcantly different from other disturbances. This result
was likely due to variance. However, this could be interpreted as the beginning of a
change in the population density of fungivores and it may have been necessary for the
soil core environment to be maintained longer to realize a signiﬁcant change in
fungivores. Chen and Ferris (1999, 2000) reported a range of 5-15 days for fungi to
colonize a substrate and the suppression of fungi growth by the presence of nematodes.
As these cores were not allowed a period of time for fungi to colonize it is certainly
possible that the fungivores present slowed the grth of fungi and thus it took longer for
the food source to increase to support a growing number of fungivores.

The alfalfa meal disturbance was had the higher population density of herbivores
while the sucrose disturbance resulted in a signiﬁcantly lower population density of
herbivores. All other controls and disturbances, except alfalfa meal, were not
distinguishable from it either. While the wide range of responses of the herbivores

cannot be explained, it is interesting to note that the use of low molecular weight organic

82

acids, such as acetic acid, has been recommended as a control for nematodes (McBride et
al. 2000). Molasses has also been recommended for control for plant-parasitic
nematodes. Possibly the addition of the carbon source encouraged the growth of
nematode antagonists. Although fungal pathogens of nematodes were periodically
observed throughout this entire project, no speciﬁc observations on this were noted
during this experiment.

There was a change observed in only one group of K-strategists, the omnivores.
Since omnivores are described as persisters, a decrease as a result of disturbance is
expected (Bongers 1990). The lowest populations were found in the acid, sucrose, and
alfalfa meal disturbances. Although these are three vastly different substances, they all
seemed to have had a detrimental effect on the omnivores. Omnivores have been
indicated as being sensitive to chemical pollution or disturbance (Blakely et al. 2002,
Tenuta and Ferris 2004). As with the herbivores, this could be the result of greater
activity from the nematode antagonists caused by these additions. Or since these are also
the disturbances with the largest bacterivore populations, it is possible that the omnivores
were unable to compete for space or food. As this was soil from a minimally disturbed
site, a high population of omnivores in the initial density is expected, but the drop in the
non-disturbed control was not. This could be demonstrating a loss of food source, as a
result of being maintained in a greenhouse while the cores from which the initial density
was determined were stored in a cold chamber at 4 °C for the duration of the experiment.
It also was not expected that the population density in the physical disturbance would be

similar to the initial population. Referring to the soil survey in Chapter 1 and the soil

83

textures (Appendix B), the presence of more sand and organic matter in this soil may
buffer the omnivores from physical changes of their environment.

Finally, the highest total population density was recovered from the alfalfa meal
disturbance. This was probably the result of the highest populations of bacterivores being
associated with this disturbance. As described by Ferris et a1. 2001 , these r-strategists
were ready to take advantage of the ﬂush of decomposers from this input of highly

decomposable organic matter.

Nitrogen

The disturbance that had the effect of increasing the total amount of NO3' and
NH4+ released from the soil cores was the alfalfa meal amendment. The amount of NO3'
and NH4+ released by this disturbance was not signiﬁcantly different on the ﬁrst day of
the experiment from all the other disturbances, but by the ﬁnal day it was signiﬁcantly
higher. The alfalfa meal added both carbon and nitrogen to the soil ecosystem and
provided an appropriate C:N ratio of organic matter to allow the microbial community to
decompose it, release NH4+, and nitrify this NH4Jr to N032 This was a greater effect than
simply increasing the oxidation of the organic matter (tillage) already present or adding a
carbon source (acid, sucrose disturbance). As nitrate is an anion, large quantities
leaching out are expected. The cation ammonium is not expected to leach in the large
amounts recovered from the alfalfa meal disturbance, so there would seem to be a larger
quantity being produced. It is likely that the bacterivores, which also increased with this
disturbance, are excreting a portion of the ammonia themselves and contributing to the

total nitrogen recovered. It can also be concluded that the bacterivore population was

84

responsible for stimulating part of the increase in nitrogen mineralization (Ingham et al.

1985, Ferris et al. 1998).

QM

Although more nitrogen was released with the alfalfa meal disturbance, this
resulted in the least carrot growth. This is maybe the result of an allelopathic effect from
the bacteria decomposing the organic matter. The products of decomposition released by
a bacterium may be allelopathic to seedlings and some of these products were probably
produced during the decomposition of the alfalfa meal (Atlas and Bartha 1998). Another
possibility is that the levels of NH4+ produced were toxic to the plants. If the carrots were
planted later in this experiment, perhaps this effect could have been avoided and the
plants may have beneﬁted from the increase in nitrogen.

The greatest carrot fresh weight was found in the physical disturbance and a
similar weight was also found in the non-disturbed control, disturbed control, and the
acid disturbance. This could be interpreted as unexpected since these disturbances are
almost opposites as structure was broken down in the disturbed control and physical
disturbance but not the non-disturbed control and the acid disturbance. Again, the sand
and organic matter content of the soil could have prevented the loss of much soil

structure and provided an ideal environment for carrot growth.

Conclusions

The alfalfa meal disturbance applied in this experiment had affects on the

nematode community structure, nitrogen dynamics, and carrot growth. The population

85

 

 

densities of bacterivores increased and the total amount of nitrogen released increased
from the soil cores. Effects on the population densities of herbivores and omnivores were
also noted among the disturbances. The response of carrot fresh weight to disturbances
that introduced a physical change to the soil or did not involve a physical change was
similar. These results may be due to the characteristics of the woodland soil which allow

it to resist some changes from physical disturbances; organic matter content.

86

Chapter 3

IMPACTS OF PHYSICAL DISTURBANCE AND AN ORGANIC AMENDMENT ON
TWO SOILS
Introduction

The organic matter and associated biota present in a soil impart its ability to hold
water and cycle nutrients. Two soils can react very differently to the same disturbance.
A soil that is tilled annually may show very few or no changes in nematode community
structure, while one that is never physically disturbed may have a dramatic change when
it is tilled. The same is true of organic amendments. The incorporation of an amendment
with a very different C :N ratio than that of the soil or different from what is usually
added to a soil can cause changes in the nematode community structure and nitrogen
dynamics of the soil.

In Experiment 3, two of the disturbances of Experiment 2 were repeated in
addition to comparing these disturbances in soil from two different sites. The objective
was to determine the effects of a physical disturbance and an alfalfa meal amendment on
nematode community structure, nitrogen availability, and carrot grth in two soils. It
was postulated that disturbance of soils from different types of ecosystems would have

different changes in nematode community structure and nitrogen dynamics.

Methods and Materials

Intact soil cores were removed from the carrot and the woodland sites, using the

same method as described for experiment two. PVC pipe containers measuring 5x15 cm

87

(z300 cm3), with a beveled edge were pushed into the soil with a fence post pounder
placed over a piece of pipe designed to ﬁt over the PVC pipe container. The containers
were then pulled out with the soil core inside. Groups of ﬁve cores were put in plastic
bags and stored at 4 °C until the experiment was started. A cap was placed on the end of
each tube into which a 2 x 3 mm screen was placed. The cap contained a hole for
collecting leachate samples for nitrogen analysis.

The soil cores were brought into a glass greenhouse at Michigan State University
on May 18, 2004, approximately 24 hours before the start of the experimental period, to
acclimate to the greenhouse temperature and to end any period of arrested activity of the
soil biota caused by storage. The soil cores appeared slightly drier than when they were
collected and were watered with 20 ml of distilled water. For the duration of the
experiment the cores were kept in the greenhouse at 24-30 °C. This greenhouse had an
east-west orientation and the walls had been white washed. The temperature was
controlled by exhaust fans and vents. Any weeds that germinated in the soil cores were
cut at the soil level or pulled as they emerged and placed on top of the soil. The cores
were strapped to a vertical board that was high enough to allow the placement of a
collection container under each core. The cores were placed in a randomized complete
block design. The cores were watered as needed with 10 ml of distilled water. All cores
were watered the day prior to collection of leachate samples as described below. Six
replicate cores of soil were disturbed in one of the following three ways:

0 A control which was non-disturbed, except for the planting of two carrots,
0 physical disturbance in which the upper 10 cm of the soil core were mixed with a

spatula,

88

0 or an organic matter amendment in which 15 cm3 of alfalfa meal (Bradﬁeld
"Gold" 3-1-5) was added to the upper 10 cm of the soil core and mixed in with a
spatula for one minute.

These disturbancess were applied on day two. On the third day, two carrot seeds (var.
Nantes Fancy Carrot, Fedco Seeds) were planted into each core with as little disturbance
as possible. The soil was gently opened with a spatula just enough to allow the carrot
seed to be inserted, and then closed again. The carrot seeds were soaked in distilled
water for three days prior to planting. The experiment was run for a total of 24 days;
May 19 to June 11, 2004.

Leachate samples were collected on days 0, 1, 6, 9, 12, 15, 18, 21, and 24 for
nitrogen analysis. The method used was according to Ferris et al. 1998. On sampling
days 60 ml of distilled water was poured on the top of the cores and a collection container
was placed underneath each core. The cores were then allowed to drain until 30 ml or
more leachate was collected in the containers but no longer than 24 hours. It was
necessary to increase the length of time that the cores were allowed to drain as some
cores drained very slowly and a longer period of time was needed to collect an
appreciable sample. The samples were then ﬁltered through #1 Whatrnan ﬁlter paper and
reﬁigerated until they were taken to the Michigan State University Soil and Plant
Nutrient Laboratory and analyzed for NO3'and NI-I4+ concentrations.

At the end of the 24 days each soil core was split into four vertical sections. Three
subsamples were placed in a bag and stored in the cold storage chamber. The remaining
subsample was used for nematode community structure analysis. The nematodes were

processed according to Jenkins (1964). These samples were then refrigerated until

89

counted. The samples were assessed for nematode community structure using direct
count microscopy. Nematodes recovered were classiﬁed according to trophic guilds:
bacterivores, fungivores, herbivores, carnivores, omnivores, and unknowns. Unknowns
included cadavers that could not be identiﬁed and live nematodes that were in a position
on the counting plate that obscured key body parts. Unknowns were not analyzed but
were included in the total population. The nematodes were identiﬁed to the lowest taxon
possible, usually superfamily although some were identiﬁed to species. The counting
plate was divided into 12 columns. Every other column was counted and the population

of each feeding group was estimated by multiplying by two.

Statistical Analysis. Data ﬁom all experiments was subjected to a random block
design analysis of variance. Means were separated using Tukey’s test (P g 0.05) or the
more liberal Least Signiﬁcant Difference test when Tukey’s test could not separate the

means.

Results
Nematode Community Structure

This experiment looked at the effects of physical disturbance and an organic
amendment on two soils. Signiﬁcant differences (P <0.001 — 0.045) among the
disturbances were detected for all trophic guilds except the fungivores, for at least one of
the soils (Table 1). The highest population of bacterivores was found in the carrot soil
with the alfalfa meal amendment. This population density is signiﬁcantly (P = 0.001)
higher than the same disturbance in the woodland soil and the controls and the physical

disturbances in both soils.

9O

In contrast to the carrot soil where no herbivores were found, 29, 28, and 41
herbivores/50 cm3 of soil were recovered ﬁ'om the control, physical, and alfalfa meal
disturbances of the woodland soil (Table 1). This is obviously a major signiﬁcant
difference (P <0.001) between these two soil/disturbance systems. The population
density of carnivores among the disturbances was signiﬁcantly different (P = 0.045) but
Tukey’s test was unable to separate these means. The populations of omnivores showed
signiﬁcant differences (P = 0.004). The most omnivores were found in the woodland,
control and the woodland disturbances and the carrot control had similar densities. The
least omnivores were in the physical disturbances of the carrot soil, but the alfalfa meal
disturbances of both soils and the carrot control were indistinguishable. The carrot
control, woodland physical disturbance, and both alfalfa meal disturbancess were all
similar to each other. Signiﬁcantly higher (P = 0.002) total populations of nematodes
were recovered from the alfalfa meal disturbances of both soils, although the woodland
soil was indistinguishable from all other disturbance/soil systems. The taxa recovered

from each soil are presented in Table 2.

Nitrogen

During the ﬁrst leaching there were no signiﬁcant differences (0.472) in the
amount of NIL;+ recovered from the soil cores, however, there were in the amount of
NO3' (0.003) (Table 3). More NO3’ was recovered from the carrot soil, but the carrot
control and physical disturbance were indistinguishable from the woodland soil. A
signiﬁcantly higher (P < 0.001) total amount of NO3' was recovered from alfalfa meal

disturbance of both soils. However, the alfalfa meal disturbance of the carrot soil was not

91

 

different from all the other disturbance/soil systems (Table 4). The alfalfa meal
disturbance of the woodland soil also showed a signiﬁcantly higher (P < 0.001) total
amount of NH4+ recovered (Table 4). The amount of NO3‘ was increased signiﬁcantly (P
= 0.003) over the experimental period in the carrot, alfalfa meal disturbance (Fig l). The
amount of NH4+ released was signiﬁcantly (P = 0.003) increased also (Fig 2). There was
also a signiﬁcant increase in the amounts of NO;,' (P < 0.001) and NIL;+ (P < 0.001)
released from the woodland, alfalfa meal disturbance (Fig 3 and 4, respectively). Figures
5 and 6 display the amounts of NO3’ and NH4+ released by each disturbance on each

leaching day and the trends they formed over the experimental period.

C_arr_9t_s

The least carrot growth (fresh weight) in both soils was associated with the alfalfa
meal amendment. The highest fresh weight was associated with the physical disturbance
(Table 5). These differences however were not statistically signiﬁcant (P = 0.270).

Carrot data is reported in Appendix C, Table 2.

92

 

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94

Table 3: Amount of NO3' and NH4+ recovered from two soils before disturbances were
applied.

 

Soil Disturbance N03' (pg) NH: (#3 )

 

 

 

- Control 0.002 ab 0.002
2 Physical 0.796 ab 0.002
U Alfalfa 1.778 a 0.002
:3 Control 0.566 b 0.004
% Physical 0.478 b 0.004
g Alfalfa 0.577 b 0.018

ﬂax: 0.003 0.472

 

95

Table 4: Total NOg' and NH4+ recovered from two soils, disturbed in two ways, over a
period of 24 days.

 

Soil Disturbance NO3' (pg) NFL:+ (ug )

 

 

 

“ Control 0.504 0.005
G
5;; Physical 0.387 0.01 1
Alfalfa 0.727 0.027
:3 Control 0.499 0.012
a
'8, Physwal 0.333 0.008
3 Alfalfa 1.056 0.250
ANOVA
P Value < 0.001 < 0.001

 

96

Figure 1: Recovery of N03’ from carrot site soil amended with alfalfa meal over an
experimental period of 24 days.

 

 

no;

 

 

ﬂ y = 0.00003123x, r2=0.153, p = 0.003

I - Actual

1 --—Predicted J .

 

 

 

 

Days

 

 

 

97

 

Figure 2: Recovery of NH4+ from carrot site soil amended with alfalfa meal over an
experimental period of 24 days.

 

 

 

 

 

 

 

 

 

NH:
0.00035 ~- A M ”MMM _ M ---,--___ _____..__
y = 0.0000018, r2 = 0.152, p = 0.003
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98

Figure 3: Recovery of NO3' from woodland site soil amended with alfalfa meal over an
experimental period of 24 days.

 

 

NO3'

 

0.008 —-— —-— —«~M M 7 MM__- - -kwi, ,,
y = 000008419, [’2 = 0.442, p < 0.001

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A

 

 

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99

 

Figure 4: Recovery of NH4+ from woodland site soil amended with alfalfa meal over an

experimental period of 24 days.

 

NH:

 

 

 

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— Predicted

 

y = 0.000018, r2 = 0.242, p < 0.001

 

 

 

 

 

 

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102

Table 5: Fresh weights of carrots associated with two different soils and two
disturbances.

 

Soil Disturbance Carrot Fresh

 

 

 

Weight (g)
Control 0.167
e
5 Physical 0.239
Alfalfa 0.001
13 Control 0092
a
1%, Ph)’81cal 0. 159
3 Alfalfa 0007
AN OVA
P Value 0270

 

103

Discussion
Nematode Community Structure

Based on the previous experiment, and previous research (Ferris et al. 1996,
2004), the alfalfa meal disturbance was expected to have the highest population of
bacterivores. The population of bacterivores in the carrot soil was signiﬁcantly higher
than all the other experimental systems. When considering the woodland soil alone, the
alfalfa meal disturbance also had the highest population compared to the control and the
physical disturbance, but it was not signiﬁcantly different compared to all the other
experimental systems. This may reﬂect a conditioning of the soil caused by different
management. The carrot soil is in an area cultivated each year and organic matter is
constantly being incorporated. As a result there are likely higher populations of
bacterivores already present that can take advantage of the incorporation of organic
matter. In the woodland these nematodes are also present but in lower densities so their
response as not as pronounced (Ferris et al. 2001). Once again, as in previous
experiments, the highest total nematode population is associated with the disturbance that
has the highest population of bacterivores.

The striking difference in the herbivores was that in the carrot soil there were
none, while the woodland soil had species from at least four genera. Previous
observations with both the carrot and the woodland soils have revealed the presence of
herbivores, but in this experiment only the herbivores in the woodland soil were found.

Turning to the K-strategists, signiﬁcant differences were found in both the
carnivore and the omnivore population densities. Using the Least Signiﬁcant Difference

test, the physical disturbance of the woodland soil was shown to have a signiﬁcantly

104

higher population of carnivores than all other experimental systems, the opposite of what
is expected of their Maturity grouping (Bongers 1990). The highest population of
omnivores was found in the woodland control. In the carrot soil the highest population of
omnivores was also in the control, but this number was not signiﬁcantly different from all
the other disturbance/soil systems. The highest populations of omnivores being found in
the controls was a predictable response, but the lack of difference from the disturbances
of the two soils was not. Omnivores are most often found in undisturbed soils, however,
disturbance did not seem to have much of an effect. It is also interesting to note that the
control of the carrot soil was not different from all the other disturbance/soil systems.
This could mean that the population of omnivores in the carrot soil is at a stable
population level and is not affected when exposed to disturbances that occur at its place
of origin. Perhaps a natural selection has occurred which has allowed certain omnivores

to survive.

Nitrogen

The total amounts of nitrogen released on the ﬁrst day clearly show that there are
differences between the two soils used. Since there was only a difference in the amount
of NO3' released and not NH4+ this could mean that there are more nitriﬁers at work in
the carrot soil. The alfalfa meal disturbances in both soils released similar and the
highest amounts of N03' for their respective experimental systems. Here there was also a
large difference in the amount of NH4+ recovered. The most NH4+ was recovered from
the alfalfa meal disturbance of the woodland soil. As the largest populations of

nematodes were found in these disturbance/soil systems, these results suggest the same

105

conclusions of Ingham et al. (1985) and Ferris et a1. (1998), that the presence of
nematodes increases the rate of nitrogen mineralization. Additionally, the alfalfa meal
disturbance of the woodland soil caused an increase in the amount of nitrogen recovered
distinguishable from that of the carrot soil. Possibly the soil organic matter of the
woodland had a high C:N ratio and the addition of the alfalfa meal provided the nitrogen
needed to decompose it. This effect was not seen in the carrot soil probably because the
soil organic matter typically has a lower C:N ratio.

When Figure 5 is considered, the N03] recovered from the alfalfa meal
disturbance of the woodland soil appears to be starting to decline. In Experiment 2 this
phenomenon was not observed. This implies that the grth of decomposers was
occurring at a faster rate, using up the available resources and mineralizing less nitrogen.
The temperature was more difﬁcult to control during this experimental period and
sometimes made it above 30 °C. This temperature increase certainly could have
increased the microbial activity inside the soil cores and speeded up all the processes they

were carrying out.

2%

The total nitrogen recovered showed differences among the alfalfa meal
disturbances and the physical disturbances and controls but the carrot fresh weights did
not. It should be noted, however, that overall there was less germination in this
experiment. Although the carrots grown in the alfalfa meal disturbances showed the
lowest weights, similar to Experiment 2, they were not signiﬁcantly different from the

controls or the physical disturbances. Again, this may be due to allelopathic

106

decomposition products released by the bacteria during the decomposition of the alfalfa
meal (Atlas and Bartha 1998). However this would not explain why the other
disturbances were not signiﬁcantly different from the alfalfa meal. Germination and
growth may have been inhibited by the high temperatures of the greenhouse as 30 °C is
outside the optimum for carrot growth. Additionally, some soil cores drained very slowly
and remained quite moist. These water logged conditions may have contributed to the

reduced carrot growth.

Conclusions

The disturbances applied in this experiment affected the nematode community
structure and nitrogen dynamics in two different soils. Considering the bacterivore
population densities, the two soils showed the same general trends but the size of the
population densities were speciﬁc to each soil. The addition of alfalfa meal increased the
amount of N03' and NH4+ recovered from the woodland soil. Higher temperatures likely
speeded up the life cycles of decomposers causing an earlier peak in N03' release during

this experiment.

107

Chapter 4
AN EXPERIMENT WITH MICROCOSOMS
Introduction

Ingham et al. (1985) built sterile microcosms and inoculated them with
populations of bacteria, fungi, and bacterial or ﬁrngal feeding nematodes. The organisms
used were isolated from a grassland land in Colorado; the ﬁrngi used were Mortierella sp.
and F usarium oxysporum, bacteria included Pseudomonas paucimobilis, and
Psedudomonas stutzer, the fungivore used was Aphelenchus avenae, and the bacterivores
used were Acrobloides sp. and Pelodera sp. Blue grama grass (Boutelous gracilis) was
the plant used. More nitrogen was mineralized in the presence of grazing nematodes as
opposed to bacteria or fungi alone and the presence of nematode grazers increased the
population densities of bacteria and ﬁmgi.

An experiment conducted as part of this Masters of Science program was
designed to further study the interactions occurring between the nematodes and bacteria
at the carrot site. Microcosms were built using soil and soil organisms isolated from the
carrot site. A major effort throughout the research was used for the identiﬁcation and
culturing of appropriate nematodes for this trial. It was postulated that more nitrogen will
be released from the cores with the nematode and bacterial slurry and that this will

enhance carrot growth.

Methods and Materials

Microcosoms were built using Pseudodiplogasteroides compositus (Komer, 1954)

and a microbial slurry cultured from the carrot site. These methods are adapted from

108

Ingham et al. (1985) and Penis et al. (1998). Nematodes were extracted from soil ﬁ'om
the site using pie pan sieves. Individual, gravid bacterivores were removed from the
suspension and placed on sterile NGM agar plates (NGM; Sulston and Hodgkin 1988).
Individual nematodes were then picked off these plates until a single lineage from one
nematode was assured. Nematodes fed on bacteria that were transferred to the plates by
either attachment to nematode bodies or being passed through their digestive system.
The nematodes were then identiﬁed as P. compositus. Voucher specimens were
preserved in FA. 4:1 ﬁxative (Seinhorst 1966) and deposited in the Entomology
Museum, Michigan State University (Appendix A, Table 4). For inoculation, the
nematodes and bacteria were washed off the agar plates and collected. This suspension
was sieved to separate the bacteria from the nematodes. The nematodes were rinsed with
water to remove associated bacteria. The combinations of organisms tested were:

I autoclaved soil control,

I autoclaved soil + bacteria,

I autoclaved soil + P. compositus ,

I autoclaved soil + bacteria + P. compositus,

I and ﬁeld soil control.

Autoclaved soil from the carrot site was used to build the columns. The soil was
autoclaved for about 6 h. After ﬁlling 5 x 15 cm PVC pipe containers with
approximately 300 cm3 of soil, they were then inoculated with the needed combinations
of organisms and sterile water. Three inoculation wells were made in the top of each
core. Approximately 700 nematodes were added in three 2 ml volumes of water. The

bacterial suspension was added in three 1 ml volumes. If one of the organisms was not

109

added to a core sterile water was added instead. For the controls 3 m1 of sterile water
were put into each well. All the wells were then smoothed over. A cap was placed on
the end of each container into which a 2x3 mm screen was placed. The cap contained a
hole for collecting leachate samples for nitrogen analysis. The cores were maintained in
a white washed, glass greenhouse. The temperature was controlled by vents and exhaust
fans (24 - 30 0C). The cores were placed in a randomized complete block design and
strapped to a vertical board that was high enough to allow the placement of a collection
container under each core. They were watered as needed with 10 ml of boiled distilled
water. All cores were watered the day prior to collection of leachate samples as
described below. The carrot seeds were sterilized in a 3% bleach solution and then pre-
soaked in distilled water prior to planting. Two seeds were planted in each container.
The experiment was run for a total of 24 days (June 5 to June 28, 2004) and consisted of
six replications of ﬁve treatments.

Leachate samples were collected on days 0, 1, 6, 12, 18, and 24 for nitrogen
analysis. The method used was according to Ferris et al. 1998. On sampling days 60ml
of distilled water was poured on the top of the cores and a collection container was placed
underneath each core. The cores were then allowed to drain for two hours or until 30 ml
of leachate were collected in the containers. The samples were then ﬁltered through #1
Whatrnan ﬁlter paper and reﬁigerated until they were taken to the Michigan State
University Soil and Plant Nutrient Laboratory and analyzed for NO3'and NH4+
concentrations.

At the end of the 24 days each soil core was split into four vertical sections. Three

subsamples were placed in a bag and stored in the cold storage chamber at 4 °C. The

110

remaining subsample was used for nematode community structure analysis. The
nematodes were processed according to Jenkins (1964) from 50 cm3 of soil. These
samples were then counted immediately using direct count microscopy.

Statistical Analysis. All data sets were subjected to random block design
analysis of variance. Tukey’s Test was used to identify differences in treatment means (P

5 0.05).

111

Figure 1: Photomicrographs of the nematode identiﬁed as Pseudodzplogasteroides
compositus (Komer, 1954) showing the esophagus (A), buccal cavity (B), and vulva (C).
Images in this thesis are presented in color.

 

112

Results
Nematodes

Of the 36 total cores inoculated with nematodes, one live nematode was
recovered. One dead nematode was found in a separate core. The cores built with ﬁeld
soil had an average of 33 nematodes. No attempt was made to quantify the bacteria in the

soil cores.

Nitrogen

The leaching that occurred before the soil cores were inoculated with organism
reveled that the autoclaved soil and ﬁeld soil were releasing signiﬁcantly different
amounts of N03' and NH4+ (Table 1). The ﬁeld soil control released much more NO3’ (P
< 0.001) and less NH4+ (P < 0.001) than the autoclaved soil. By the end of the
experimental period, however, a similar amount of total NO3' had been recovered from
all of the treatments (Table 2). The total amount of NH; recovered was still signiﬁcantly
different (P < 0.001). The cores built with autoclaved soil released more NH4+ than those
built with ﬁeld soil. The amount of NO3' and NH4+ recovered on each leaching day and
the trends formed are displayed in Figures 1 and 2, respectively.

C_a_1'1'_0_t§

The carrot weights ranged from 0.637 g in the ﬁeld soil control to 0.182 g in the
autoclaved soil control (Table 3). Carrot fresh weights were not signiﬁcantly different
among the treatments at the 0.05 level but were at the 0.10 level (P = 0.052). The ﬁeld
soil produced a signiﬁcantly higher carrot fresh weight than the autoclaved soil control.

However, the autoclaved soil with the bacteria, P. compositus, and bacteria and P.

113

compositus were not distinguishable from either control. Appendix C, Table 3, reports

the carrot data collected for this experiment.

114

Table 1: Amount of NO3’ and NH4+ recovered from soil cores before organisms were
inoculated.

 

Treatment NO3‘ (pg) NH: (pg)
A“‘°°'.“e" 0.963 b 0.930 a
Son]
Autoclaved
Soil & 0.583 b 0.791 a
P. compositus

Autoclaved
Soil & bacteria 0'627 b 1.030 a

Autoclaved
Soil & bacteria

&
P. compositus

Field Soil 2.211 a 0.040 b

AN OVA
P Value

 

0.336 b 0.954 a

 

< 0.001 < 0.001

115

Table 2: Total NO3’ and N114+ associated with two controls and three microcosms
inoculated with soil organisms.

 

 

 

Treatment N0; ([3) N114+ ([3)
”may“ 0.608 0.504 a
8011
Autoclaved
Soil & 0.768 0.522 a
P. compositus
Autoclaved
Soil & bacteria 0983 0546 a
Autoclaved
Sorl &;acterra 0.937 0.574 a
P. compositus
Field Soil 1.193 0.021 b
ANOVA
P Value 0.263 < 0.001

 

 

116

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118

Table 3: Fresh weights (g) of carrots associated with two controls and three microcosms
inoculated with soil organisms.

 

 

Treatment Total Fresh
Weight (g)
Autoclaved Soil 0.182
Autoclaved Sol] & 0.268
P. composztus
AutoclavedSoﬂ & 0.402
bacteria
Autoclaved Soil &
bacteria & 0335
P. compositus
Field Soil 0.637
ANOVA
P Value 0-052

 

 

119

Discussion
Nematodes

The hypothesis stated was not supported by this experiment. The absence of
nematodes in the cores built with autoclaved soil did, however, verify efﬁcacy of the soil
sterilization method for removal of nematodes. The absence of nematodes in the
inoculated cores could be explained in several ways. The inoculation of nematodes and
bacteria at the same time may not have provided an adequate food source. This is quite
likely as no incubation period was provided for the bacteria to colonize the soil before it
was grazed by the nematodes. After the nematode population died, however, the bacteria
may have again started to colonize the soil. Another possibility is that the autoclaving
may have made something about the soil toxic to the nematodes. Finally, the nematode
chosen may not have been suitable for colonizing the cores aﬁer being reared on agar
plates. The agar plates contained cholesterol, a needed additive since nematodes cannot
manufacture their own sterols. The soil, however, was not amended with cholesterol.
This may have created too much stress on the nematodes, coupled with being moved

from one environment to a completely different one.

Nitrogen

Differences in the amount of N03” and NH4+ were expected because the soil was
treated so very differently; autoclaved or not. These differences were seen clearly in the
nitrogen leached on the ﬁrst day. Increases in the amounts of NO3’ and NH4+ released
from autoclaved soil were observed by Lopes and Wollum (1976). In view of this the

large amount of NH4+ released was expected, however, signiﬁcantly less NO; recovered

120

from the autoclaved soil compared to the ﬁeld soil was not expected. This could be a
result of the soil cores being in the warm greenhouse for approximately 24 hours before
the experiment began. The soil organisms in the ﬁeld soil may have mineralized a lot of
nitrogen before the cores were leached. In addition to the warm temperatures of the
greenhouse, all the soil had been mixed to build the cores and this process may have
exposed some more organic matter for decomposition.

Considering Figure 2, the large totals of NIL;+ recovered ﬁ'om the autoclaved soil
appear to have been released at the beginning of the experimental period and then
steadily decreased over the rest of the period. The NH; of the ﬁeld soil, with the whole
complement of soil bacteria, did not change much over the time of the experiment. Since
this soil was not autoclaved it had the correct bacteria to continue converting NIL;+ to
N03} as in the previous two experiments. The total NO3' recovered also followed a trend

similar to those in Experiments 2 and 3.

9m

Although the bacteria were not quantiﬁed, the similarity of the carrot ﬁ'esh
weights from the ﬁeld soil control and the autoclaved soil with bacteria, with P.
compositus, and with bacteria and P. compositus suggests that there were some bacteria
present in the core. These bacteria appeared to enhance the grth of the carrots,
probably by supplying nutrients through decomposition of soil organic matter. The
carrots growing in the autoclaved soil also displayed yellowing of the leaves, probably
the result of a nutrient deﬁciency. This may be why they were not distinguishable from

the carrots growing in the autoclaved soil control.

121

Conclusions

Although this experiment was essentially a failure in relation to the objectives, it
did show that the speciﬁc autoclaving procedure used worked well for eliminating
nematodes from soil. The ﬁndings of Lopes and Wollum (1976) in relation to NH;
release from autoclaved soil were supported. The same ﬁndings in relation to NO3' may
have been supported too if the autoclaved and ﬁeld soil had been leached before being
placed in the greenhouse. The importance of a biologically active soil to the grth of

plants was demonstrated again.

122

Thesis Summary and Conclusions

The primary objective of this project was to observe the effects that different
types of soil ecosystem disturbance have on nematode community structure, nitrogen
dynamics, and carrot growth in relation to how these changes can be used to describe soil
quality. It was postulated that ﬁmdamental physical, chemical, and biological
disturbances cause changes in nematode community structure and nitrogen dynamics that
affect carrot growth.

Chapter 1 consisted of a survey of three sites and Experiment 1. The survey
showed many differences and some surprising similarities among the three sites that have
been managed differently for many years. The fundamental disturbances applied in
Experiment 1 affected the nematode community structure of soil cores maintained under
greenhouse conditions. In particular, the physical disturbance and the disturbed control
(structure of the entire soil core destroyed) exhibited the greatest changes in the
population densities of both r— and K-strategists.

In Experiment 2, disturbances applied to soil cores collected from the minimally
disturbed woodland had affects on the nematode community structure, nitrogen
dynamics, and carrot growth. The alfalfa meal amendment showed the greatest effect by
increasing the population density of bacterivores and increasing the total amount of
nitrogen released from the soil cores. The response of herbivores and omnivores was not
typical of K-strategist response to disturbance. Both disturbances that introduced
physical change of the soil and those not involving a physical change resulted in an

increase in the fresh weights of carrots.

123

Experiment 3 repeated two of the disturbances studied in Experiment 2; however,
two soils (carrot site and woodland) were used. The woodland cores reacted similarly to
those of Experiment 2. The carrot site cores showed the same general reactions to the
disturbances, but population densities of the trophic roles were speciﬁc to each soil. The
addition of alfalfa meal increased the amount of NO3' and NH: recovered from both
soils, but the increase in N03' released from the carrot soil was not signiﬁcantly different
from the carrot soil control. This suggests a difference in the C :N ratios of the organic
matter in these soils.

Experiment 4 failed to prove the hypothesis. It did, however, verify the
effectiveness of the speciﬁc autoclaving procedure used for eliminating nematodes from
soil. It also showed that autoclaving will cause signiﬁcant changes in the chemical
properties of soil.

The objectives of this project were met and the overall general hypothesis was
conﬁrmed by these research ﬁndings. Observations were made on the affect different
types of disturbance have on nematode community structure, nitrogen mineralization, and
carrot growth. Part of the ﬁndings of this project was in contrast to some previous
research while other ﬁndings veriﬁed previous research. The responses of nematode
community structure to disturbance observed in this project were expected based on the
works of Bongers and Ferris in various recent articles on nematode commmiity ecology,
nutrient mineralization, and ecosystem management. This was, however, in contrast to
the ﬁndings of Parmelee and Alston (1986) and Freckman and Ettema (1993) in ﬁeld
studies. Relationships between nitrogen mineralization and bacterivore populations

veriﬁed the ﬁnds of Ingham et al. 1985 and Ferris et al. 1998.

124

In conclusion, soils will exhibit different and predictable responses to
disturbances. The predictability of these responses could allow different disturbances to
be suggested for a soil to promote needed changes in the soil food web to increase
nutrient mineralization or manage populations of plant-parasitic nematodes. Further

study will be needed to make this practical for grower use.

125

APPENDICES

126

Appendix A
Record of Deposition of Voucher Specimens“
The specimens listed on the following sheet(s) have been deposited in the named
museum(s) as samples of those species or other taxa, which were used in this research.
Voucher recognition labels bearing the Voucher No. have been attached or included in
ﬂuid-preserved specimens.
Voucher No.: 2004-03

Title of thesis or dissertation (or other research projects):

Impacts of Soil Ecosystem Disturbance on Nematode Community Structure

Museum(s) where deposited and abbreviations for table on following sheets:

Entomology Museum, Michigan State University (MSU)

Other Museums:

Investigator’s Name(s) (typed)
Jessica Jean Smith

 

 

Date August 16. 2004

*Reference: Yoshimoto, C. M. 1978. Voucher Specimens for Entomology in North America.
Bull. Entomol. Soc. Amer. 24: 141-42.

Deposit as follows:
Original: Include as Appendix 1 in ribbon copy of thesis or dissertation.

Copies: Include as Appendix 1 in copies of thesis or dissertation.
Museum(s) ﬁles.
Research project ﬁles.

This form is available from and the Voucher No. is assigned by the Curator, Michigan State University
Entomology Museum.

127

Appendix A

Table 1: Voucher Specimen Data for carrot site, Nodding Thistle Farm

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Appendix A

Table 2.A: Voucher Specimen Data for woodland, Nodding Thistle Farm

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129

Appendix A

Table 2.B: Voucher Specimen Data for woodland, Nodding Thistle Farm

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Appendix A

Table 3: Voucher Specimen Data for corn ﬁeld, Norm Sandbrook’s Farm

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M w d o A A h N B
me 89:32

131

 

Pages

Appendix A
of 5

Page 5

888888 :88: mo 88> N

 

Table 4: Voucher Specimen Data for Pseudodiplogasteroides compositus

 

 

 

 

 

 

 

 

 

 

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135

Appendix C
Carrot Data

Table 1: Carrot data associated with Experiment 2.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number Carrots
Disturbance Replication of Carrot 1 (9) Carrot 2 (9) 1 + 21g)_

Carrots Shoot Root Shoot Root Total Wt.
1 1 0.087 0.201 0.288
g .0 2 1 0.103 0.286 0.389
g g .3 3 1 0.036 0.201 0.237
2 E 8 4 1 0.142 0.339 0.481
a 5 1 0.075 0.218 0.293
6 2 0.144 0.076 0.169 0.331 0.720
1 1 0.101 0.049 0.150
'3 3 2 2 0.073 0.018 0.046 0.048 0.185
g .3 3 2 0.046 0.027 0.009 0.033 0.115
E 8 4 2 0.087 0.049 0.083 0.051 0.270
a 5 1 0.146 0.122 0.268
6 1 0.068 0.157 0.225
a 1 2 0.066 0.137 0.037 0.034 0.274
'8 g 2 0 0.000
.3 g 3 2 0.057 0.079 0.043 0.166 0.345
g 3 4 2 0.129 0.34 0.094 0.163 0.726
°- g 5 2 0.095 0.157 0.153 0.057 0.462
6 1 0.132 0.065 0.197
a 1 2 0.131 0.118 0.123 0.049 0.421
g 2 0 0.000
g g 3 0 0.000
< 3 4 1 0.118 0.073 0.191
g 5 1 0.12 0.216 0.336
6 2 0.096 0.052 0.083 0.102 0.333
a 1 1 0.128 0.03 0.158
a g 2 1 0.021 0.017 0.038
g g 3 1 0.016 0.02 0.036
g g 4 1 0.025 0.025 0.050
”’ g 5 1 0.062 0.021 0.083
6 2 0.07 0.017 0.069 0.033 0.189
_ o 1 1 0.003 0.007 0.010
g g 2 0 0.000
f g 3 1 0.062 0.017 0.079
2;; 3 4 1 0.008 0.029 0.037
3 g 5 0 0.000
6 0 0.000

 

 

136

Table 2: Carrot data associated with Experiment 3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number Carrot 1 (g) Carrot 2(9) Carrots
Disturbance Replication @3211... Shoot Root Shoot Root 1 + 2 (9)

1 1 0.1 18 0.208 0.326

. _ 2 1 0.104 0.345 0.449

E g 3 0 0.000

g 5', 4 0 0.000

5 1 0.052 0.093 0.145

6 1 0.021 0.061 0.082

_ 1 0 0.000

,5} 3 2 1 0.174 0.425 0.599

g. g 3 2 0.09 0.83 0.081 0.071 1.001

q. g 4 0 0.000

‘g g 5 0 0.000

8 0 6 0 0.000

7 0 0.000

1 0 0.000

2'5 o 2 0 0.000
a 0

~12- ; g 3 0 0.000

J, g g 4 0 0.000

g E 5 0 0.000

3 a 6 1 0.002 0.008 0.010

7 0 0.000

1 0 0.000

1; a 2 1 0.131 0.341 0.472

g a 3 0 0.000

3 5 4 1 0.048 0.031 0.079

‘3’ ° 5 0 0.000

6 0 0.000

1 2 0.038 0.042 0.019 0.029 0.099

- _ 3 2 1 0.073 0.05 0.123

E g g 3 2 0.066 0.047 0.013 0.01 0.126

%’ ﬁg 4 1 0.144 0.135 0.279

8 f 3.3. 5 2 0.066 0.101 0.166 0.111 0.333

3 a 6 0 0.000

7 0 0.000

1 0 0.000

. 7, 3 2 1 0.021 0.028 0.049

'° ° = 3 0 0.000
5 E a

a g g 4 0 0.000

8 g g 5 0 0.000

3 < a 6 0 0.000

7 0 0.000

 

137

 

Table 3: Carrot data associated with Experiment 4.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Number Carrot 1 (9) Carrot 2(19) Car-{02$

Treatment Replication Carr: ts Shoot Root Shoot Root (9)

1 1 0.22 0.16 0.38

2 2 2 0.1 0.15 0.06 0.03 0.34
g g 3 0 0

g «n 4 2 0.04 0.02 0.05 0.04 0.15

2 5 1 0.09 0.13 0.22
6 0 0

1 2 0.23 0.25 0.28 0.09 0.85

g + .2 2 1 0.5 0.22 0.72
71: = g 3 0 0
3 3 g 4 1 0.05 0.07 0.12
3 m 5 2 0.23 0.14 0.12 0.13 0.62
6 1 0.06 0.04 0.1

a 1 2 0.3 0.06 0.22 0.1 0.68

E n: g 2 1 0.08 0.1 0.18
g + 8 3 0 0
3 E g 4 1 0.13 0.16 0.29
2 w 3 5 2 0.15 0.18 0.06 0.07 0.46
6 0 0

1 2 0.07 0.05 0.15 0.05 0.32

E 9; 3 2 1 0.04 0.04 0.08
2 ; g '5 3 1 0.18 0.1 0.28
§ 3 E E 4 2 0.13 0.1 0.33 0.25 0.81

2 33 g 5 2 0.11 0.009 0.15 0.1 0.369
6 1 0.07 0.08 0.15

1 1 0.64 0.53 1.17

g 2 1 0.12 0.09 0.21

tn 3 1 0.28 0.24 0.52

§ 4 1 0.1 0.19 0.29

E 5 2 0.37 0.13 0.14 0.13 0.77

6 2 0.43 0.15 0.14 0.14 0.86

 

 

 

 

 

 

 

 

138

LITERATURE CITED

139

Literature Cited

Atlas, RM. and Bartha, R. 1998. Microbial Ecology: Fundamentals and Applications.
Menlo Park, California, Addison Wesley Longman, Inc., p.694.

Baird, SM. and Bernard, EC. 1984. Nematode Population and Community Dynamics
in Soybean-Wheat Cropping and Tillage Regimes. Journal of Nematology 16(4): 379-
386.

Bemey, M.F. and Bird, G.W. 1992. Distribution of Heterodera carotae and
Meloidogyne hapla in Michigan carrot production. Journal of Nematology 24(48):776-
778.

Bemey, M.F. 1994. Study of the Biology and Ecology of Heterodera carotae (Jones,
1950) in Michigan. Ph.D. Dissertation, Department of Entomology, Michigan State
University, East Lansing.

Bird, G.W., Bemey, M.F., and Cavigelli, M.A. 1998. Soil Ecology. In: Cavigelli, M.A.,
S.R. Deming, L.K.Probyn and R.R.Harwood (eds.) Michigan Field Crop Ecology:
Managing biological processes for productivity and environmental quality. Michigan
State University Extension Bulletin E-2646, 92 pp.

Bird, G.W., and H. Melakeberhan. 1993. Avoidance and Management of Nematode
Problems in Tree Fruit Production in Michigan. East Lansing: Michigan State
University Extension Bulletin E-2419.

Blakely, J .K., Neher, D.A., and Spongberg, A.L. 2002. Soil invertebrate and microbial
communities, and decomposition as indicators of polycyclic aromatic hydrocarbon
contamination. Applied Soil Ecology 21: 71-88.

Blair, J .M., Bohlen, P.J., and Freckman, D.W. 1996. Soil Invertebrates as Indicators of
Soil Quality. In: Doran, J .W. and Jones, A.J. (eds.) Methods for Assessing Soil Quality.
Soil Science Society of America, Inc. Madison, Wisconsin, pg. 273-292.

Bongers, T. 1990. The maturity index: an ecological measure of environmental
disturbance baxed on nematode species composition. Oecologia 83: 14—19.

Bongers, T. and Bongers, M. 1998. Functional diversity of nematodes. Applied Soil
Ecology 10: 239-251.

Bongers, T. and Ferris, H. 1999. Nematode community structure as a bioindicator in
environmental monitoring. Trends in Evolution and Ecology 14 (6): 224-228.

140

Cavigelli, M.A. 1998. Carbon. In: Cavigelli, M.A., S.R. Deming, L.K.Probyn and
R.R.Harwood (eds.) Michigan Field Crop Ecology: Managing biological processes for

productivity and environmental quality. Michigan State University Extension Bulletin E-
2646, 92 pp.

Chen, J. and Ferris, H. 1999. The effects of nematode grazing on nitrogen
mineralization during fungal decomposition of organic matter. Soil Biology and
Biochemistry 31: 1265-1279.

Chen, J. and Ferris, H. 2000. Growth and nitrogen mineralization of selected fungi and
fungal-feeding nematodes on sand amended with organic matter. Plant and Soil 218: 91-
101.

Cobb, NA. 1914. Nematodes and their relationships. US Department of Agriculture
Yearbook: 457-490.

Ferris, H., Venette, R.C., van der Meulen, HR, and Lau SS. 1998. Nitrogen
mineralization by bacterial-feeding nematodes: veriﬁcation and measurement. Plant and
Sci], 203: 159-171.

Ferris, H., Venette, R.C., and Lau SS. 1996. Dynamics of nematode communities in
tomatoes grown in conventional and organic farming systems, and their impact on soil
fertility. Applied Soil Ecology 3: 161-175.

Franzluebbers, A. J. and Arshad, M.A. 1997. Particulate Organic Carbon Content and
Potential Mineralization as Affected by Tillage and Texture. Soil Science Society of
America Journal, 61:1382-1385.

Freckman, D. W. and Ettema, CH. 1993. Assessing nematode communities in
agroecosystems of varying human intervention. Agriculture, Ecosystems and
Environment, 45: 239-261.

Gibbons, L.M. 2002. General Organization. In: The Biology of Nematodes, edited by
Donald L. Lee, pp. 31-59. New York: Taylor & Francis.

Graney, L.S.O. 1985. Observations on the morphology of Heterodera carotae and
Heterodera zvenae in Michigan. Journal of Nematology 17: 519.

Grifﬁths, B.S., Ritz, K., and Wheatley, RE. 1994. Nematodes as indicators of enhanced
microbiological activity in a Scottish organic farming system. Soil Use and management
10: 20-24.

Huang, SP. and Cares, J .H. 1995. Community Composition of Plant-parasitic
Nematodes in Native and Cultivated Cerrados of Central Brazil. Journal of Nematology
27(2): 237-243.

141

Hunt, H.W., Coleman, D.C., Ingham, E.R., Ingham,R.E., Elliott, E. T., Moore, J .C.,
Rose, S.L., Reid, CPR and Morley, CR. 1987. The detrital food web in a shortgrass
prairie. Biology and Fertility of Soils, 3: 57-68.

Ingham, E. 2000. Soil Biology Primer. Soil and Water Conservation Society. 48 pp.

Ingham, R.E., Trofymow, J .A., Ingham, ER, and Coleman, DC. 1985. Interactions of
Bacteria, Fungi, and Their Nematode Grazers: Effects on Nutrient Cycling and Plant
Growth. Ecological Monographs, 55(1): 119-140.

Korcak, RF. 1992. Early Roots of the Organic Movement: A Plant Nutrition
Perspective. HortTechnology 2(2): 263-267.

Kotecha, P.M., Desai, BB, and Madhavi, D.L. 1998. Carrot. In: Handbook of
Vegetable Science and Technology. Eds. D.K. Salunkhe and SS. Kadam. Marcel
Dekker, Inc., New York, 119-139.

Lee, D.L. 2002. Cuticle, Moulting and Exsheathment. In: The Biology of Nematodes,
edited by Donald L. Lee, pp. 291-320. New York: Taylor & Francis.

Lopes, AS. and Wollum, A.G.. 1976. Comparative effects of methyl bromide,
propylene oxide, and autoclave sterilization on speciﬁc soil chemical characteristics.
Turrialba 26: 351-355.

MacGuidwin, A.E. 1989. Distribution of Pratylenchus scribneri between Foot and Soil
Habitats. Journal of Nematology 21(3): 409-415.

McBride, R.G., Mikkelsen, R.L., and Barker, KR. 1999. Survival and infection of root-
knot nematodes added to soil amended with rye at different stages of decomposition and
cropped with cotton. Applied Soil Ecology 13: 231-235.

McBride, R.G., Mikkelsen, R.L., and Barker, KR. 2000. The role of low molecular
weight organic acids from decomposing rye in inhibiting root-knot nematode populations
in sol. Applied Soil Ecology 15(3): 243-251.

McNeill, J .R. and Winiwarter, V. 2004. Breaking the Sod: Humankind, History, and
Soil. Science 304: 1627-1629.

McSorley, R. and Dickson, D.W. 1995. Effect of tropical rotation crops on Meloidogyne
incognita and other plant-paasitic menatodes. Journal of Nematology 27: 535-544.

Neher, D.A. 1999. Nematode Communities in Organically and Conventionally Managed
Agricultural Soils. Journal of Nematology 31(2): 142-154.

Parmelee, R. W. and Alston, D.G. 1986. Nematode Trophic Structure in Conventional
and No—Tillage Agroecosystems. Journal of Nematology 18(3): 403-407.

142

Paul, EA. and Clark, RE. 1996. Closing the Nitrogen Cycle: Return of Nitrogen to the

soil. In: Soil Microbiology and Biochemistry. New York: Academic Press, pgs. 215-
243.

Peirce, LC. 1987. Vegetables: Characteristics, Production, and Marketing. New York:
John Wiley and Sons, 433 pg.

Phan, CT and Hsu, H. 1973. Physical and chemical changes occurring in the carrot root
during growth. Canadian Journal of Science 53: 629-634.

Rubatzky, V.E. and Yamaguchi, M. 1997 . World vegetables: principles, production, and
nutritive values. New York: Chapman & Hall; Florence, KY: International Thompson
Pub.

Rubatzky, V.E., Quiros, CF, and Simon, P.W. 1999. Carrots and Related Vegetable
Umbelliferae. CABI Publishing, New York, 294 pg.

Seinhorst, J .W. 1966. Killing nematodes for taxonomic study with hot f.a. 4:1.
Nematologica 12(1): 178.

Sikora, L.J. and Stott, DE. 1996. Soil Organic Carbon and Nitrogen. In: Methods for
Assessing Soil Quality, Soil Science Society of America Special Publication 49.

Simon, P.W., Matthews, W.C., and Roberts, RA. 2000. Evidence for simply inherited
dominant resistance to Meloidogynejavanica in carrot. Theoretical and Applied Genetics
100: 735-742.

Slinger, LS. 1976. Ontogeny of Daucus carota in relation to Meloidogyne hapla with a
preliminary endomycorrhizae study. MS. Thesis, department of Entomology, Michigan
State University, East Lansing.

Slobodian, N., Van Rees, K., and Pennock, D. 2002. Cultivation-Induced Effects on
Belowground Biomass and Organic Carbon. Soil Science Society of America Journal,
66: 924-930.

Tenuta, M. and Ferris, H. 2004. Sensitivity of Nematode Life-History Groups to lens
and Osmotic Tensions of Nitrogenous Soultions. Journal of Nematoloty 36(1): 85-94.

Thoen, GE 1990. Soil Survey of Barry County, Michigan. United States Department
of Agriculture, Soil Conservation Service ; in cooperation with Michigan Agricultural
Experiment Station, Michigan Department of Agriculture, and Michigan Technological
University, pg. 111.

Tu, C., Koenning, SR, and Hu, S. 2003. Root-Parasitic nematodes enhance soil
microbial activities and nitrogen mineralization. Microbial Ecology, 46: 134-144.

143

Vrain, TC. and Baker, LR. 1980. Reaction of hybrid carrot cultivars to Meloidogyne
hapla. Canadian Journal of Plant Pathology 2: 163-168.

Wang, M. and Goldman, LL. 1996. Resistance to root knot nematode (Meloidogyne

hapla Chitwood) in carrot is conrolled by two recessive genes. Journal of Heredity
87(2): 119-123.

Wardle, D.A., Yeates, G.W., Watson, RN, and Nicholson, KS. 1995. The detritus
food-web and the diversity of soil fauna as indictors of disturbance regimes in agro-
ecosystems. Plant and Soil 170: 35-43.

Warner, R. Tenney, A. and Bird, G. 2004. Avoid lesion nematodes. Michigan State
University Extension, Landscape Crop Advisory Team Alert 19 (11): 3-4.

Wyss, U. 2002. Feeding Behaviour of Plant-Parasitic Nematodes. In: The Biology of
Nematodes, edited by Donald L. Lee, pp. 291-320. New York: Taylor & Francis.

Yeates, G.W. 1979. Soil Nematodes in Terrestrial Ecosystems. Journal of Nematology,
11(3): 213-229.

Yeates, G.W., Bongers, T., De Goede, R. G. M., Freckman, D. W., and Georgieva S. S.
1993. Feeding Habits in Soil Nematode Families and Genera - An Outline for Soil
Ecologists. Journal of Nematology, 25(3): 315-331.

Yeates, G.W. 1998. Feeding in Free-living Soil Nematodes: A Functional Approach.

In: The Physioology and Biochemistry of Free-living and Plant —Parasitic Nematodes,
edited by R.N. Perry and DJ. Wright, pp.245-269. New York: CAB. International.

144

   

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