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THESIS

This is to certify that the

thesis entitled
Differential effects of simazine and diuron on
survival, growth and physiology of Populus clones.
presented by

Oluyemisi Amos Akinyemiju

has been accepted towards fulfillment
of the requirements for

Ph.D. degree in Forestry

 

Major professor

Date November ”I, 1980

0-7639

 

 

 

OVERDUE FINES:
\
25¢ per ‘0 per Item

RETURNING LIBRARY MATERIALS.
Place in book return to

hallo
charge from circulation reco

r\”,
7 7 \

DIFFERENTIAL EFFECTS OF SIMAZINE AND DIURON ON
SURVIVAL, GROWTH AND PHYSIOLOGY OF POPULUS CLONES

By

Oluyemisi Amos Akinyemiju

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Forestry

1980

cm, :73

ABSTRACT

DIFFERENTIAL EFFECTS OF SIMAZINE AND DIURON ON
SURVIVAL, GROWTH AND PHYSIOLOGY OF POPULUS CLONES

BY

Oluyemisi Amos Akinyemiju

Field and greenhouse studies were performed to
evaluate the differential effects of simazine (2-chloro-4,
6-bis (ethylamino) — s - triazine) and diuron (3-(3,4-
dichlorophenyl) - l, l—dimethyl urea) on survival, growth
and physiology of Populus clones. In field studies on
three plantation sites in lower Michigan, clonal differ-
ences in establishment, growth and biomass yield of several
Populus clones was demonstrated in response to application
of simazine and diuron. The response of clones to simazine
and diuron followed similar pattern. High doses of each
herbicide were toxic to all clones except H 47, which ap-
peared to be relatively resistant. Simazine at 2 kg/ha
was found adequate for acceptable weed control, survival
and biomass yield at the Tree Research Center (TRC) and
Dansville, At Manistee, however, simazine was ineffective
due to the low pH of the surface soil and the presence of
resistant weed species, but diuron at 2 kg/ha was suitable.

A single initial tillage at the beginning of the

season benefitted all clones tested at all herbicide rates;

Oluyemisi Amos Akinyemiju

survival, growth and biomass yield were higher on tilled
than untilled plots. Supplementing tillage with herbi-
cides further increased survival and growth of the clones
above what was obtained with tillage or herbicide alone.

At the TRC plantation, simazine caused an increase
in total foliar nitrogen of Populus clones beyond that
caused by elimination of competing vegetation. The stim-
ulatory effect of simazine on total foliar nitrogen was
dependent on clone, rate of simazine and length of time
after application. Clone H 47 and NC 5323 treated with
2 to 3 kg/ha simazine gained nearly 12% in total foliar
nitrogen over the untreated weed-free control at the
middle of the season, the period of most active growth.
Nitrogen contents of clone NE 388 and NE 48 were unaf-
fected, but height growth of NE 388 was significantly in-
hibited by simazine.

In one greenhouse study 21 Populus clones from
section Tacamahaca and Aigeiros were assayed for tolerance
to five levels of simazine and diuron. Selected clones
included both intra— and intersectional hybrids as well
as pure 2. deltoides. Each of the clones could be classi-
fied as tolerant, intermediate or intolerant to simazine
or diuron. Tacamahaca hybrids and intersection crosses
between Tacamahaca and Aigeiros were relatively intolerant
of both herbicides, whereas Aigeiros clones were relatively

tolerant. Examples of intolerant clones include

Oluyemisi Amos Akinyemiju

2. maximowiczii x g. trichocggpa (NE 388) and g. maximowi-
gag; x 2. cv. 'berolinensis' (NE 48). The E. x 33;-
americana clones 'Canada blanc' (NC 5323) and 'I 45/51'
(NC 5328) were among the most tolerant tested. A select-
ivity index with simazine of ca. 11 between NC 5328 and

NE 388 was calculated.

In a second greenhouse study, additions of 5 mg/
pot of simazine had no deleterious morphological or physio-
logical effects on NC 5328 (Aigeiros) but reduced the rate
of CO2 fixation, increased CO2 compensation concentrations
and lowered the specific leaf weight of NE 388 (Tacamahaca).
The deleterious effects of simazine on NE 388 were detected
ca. 48 hr after exposure of plants to simazine and generally
became more pronounced thereafter. Visual symptoms of in-
jury were evident at ca. 2 week after simazine application.

Toxic responses to simazine in intolerant Clone NE
388 were different depending on the position of the crown
that was sampled. Inhibition of photosynthesis and in-
creased CO2 compensation points were more pronounced in the
region of recently mature leaves, but somewhat less in the
region of expanding leaves. The lower crown region con-
sisting of older mature leaves showed no visual symptoms
of injury; rate of photosynthesis and 002 compensation con-

centration were unaffected.

Ol uy emi si Amos Akinyemi j u

Differential physiological and morphological re-
sponses to simazine and diuron among clones in greenhouse
studies confirmed the varying clonal responses to the-her-

bicides observed in the field.

This dissertation is dedicated to all
Those in search for knowledge: That in
Patience they may find and
Perseverance overcome.

ii

ACKNOWLEDGEMENTS

I am grateful to Dr. Donald Dickmann for his pa-
tience and understanding in providing guidance and leader-
ship through—out the course of my graduate studies. My
gratitude to him also for his support for the final phase
of the program.

My sincere gratitude to members of my graduate com-
mittee: Drs. W.F. Meggitt, J.B. Hart and M. Koelling for
their suggestions and review of the manuscript. I am
equally grateful to Drs. Donald Penner, Al Putman, James
Hanover, Larry Tombaugh and Ajcvi Scott-Emuarkpor who made
themselves and/or laboratory facilities accessible to me.
Much thanks also to Mike Morin of the Packaging Corp of
America, Filer City, Michigan; Dr. Alford R. Harris and
Mr. Bruce A. Birr both of North Central Forest Exp. Station,
East Lansing, for their technical assistance.

I am grateful to my friends Ed Allen, Mike O'Connor,
Eugene Eriobu, Tom Stadt, Chris Taylor and members of the
physiology-silviculture group of RM 204 Natural Resources
Building for their understanding, moral and valuable tech-
nical support.

I gratefully acknowledge the support of the Federal

Government of Nigeria for funding my graduate work.

Finally, much gratitude and love. to my wife Grace
for typing the draft copies of this dissertation, and for
her patience and understanding; to my children, Olubunmi
and Omotomilayo for their tacit understanding of my long

and frequent absence from them.

iv

TABLE OF CONTENTS‘

LIST OF TABLES.
LIST OF FIGURES .
CHAPTER I. INTRODUCTION.

Page
vi

ix

CHAPTER II. THE EFFECT S OF TILLAGE AND HERBICIDES
(SIMAZINE AND DIURON) ON THE ESTABLISH-
MENT OF POPLAR PLANTATIONS AT DIFFERENT
LOCATIONS IN LOWER MICHIGAN . . .

Introduction. . . . . . . .
Materials and Methods . . . . . . . . .
Results . . . . . . . . . . . . . .
Discussion. . . . . . . . . . . . . . . .

CHAPTER III.THE INFLUENCE OF SIMAZINE ON TOTAL
NITROGEN AND PHOSPHORUS CONCENTRATIONS
IN FOLIAGE OF FIELD-GROWN POPLAR CLONES .

IntrOduc tion- I o u e o u I I o I e a 0

NH
\OO\\O\) \)

Materials and Methods .
Results and Discussion.

CHAPTER.IV. DIFFERENTIAL TOLERANCE OF POPULUS CLONES

TO SIMAZINE AND DIURON.

Introduction. .
aaterials and Methods .

Results . . . . . . .

Discussion. . . . .

CHAPTER V. EFFECT OF SIMAZINE ON PHOTOSYNTHETIC CO
FIXATION, 002 COMPENSATION POINT, LEAF
STOMATAL CONDUCTANCE AND SPECIFIC
LEAF WEIGHT OF SIMAZINE- TOLERANT AND

INTOLERANT POPULUS SCLONES .

Introduction. . . .
Materials and Methods .
Results . . . . . . .
Discussion. . . . . . . .

CHAPTER VI. SUMMARY AND CONCLUSIONS .
BIBLIOGRAPHY. . . . . .

70

7O
72

82

94

LIST OF TABLES

Table Page

2.1 Soil properties of the experimental planta-
tion sites. . . . . . . . . . . . . 11

2.2 Parentage of Populus clones planted on the
three experimental plantation sites . . . . 13

2.3 The effect of simazine on survival and
height growth of Egpulus hybrids in their
first growing season on tilled and untilled
sites in lower Michigan (TRC) . . . . . . . . l7

2.# First-year survival and height growth of
four Populus hybrids established with varying
levels of simazine in lower Michigan, (TRC) . 19

2.5 The effect of simazine on survival, growth
and biomass yield of ngulus hybrids during
their second growing season on tilled and
untilled sites in lower Michigan, (TRC) . . . 21

2.6 Second-year survival and height growth of
four Populus hybrids established with simazine
in lower Michigan . . . . . . . . . . . . . 22

2.7 The effect of simazine and diuron on sur-
vival and height growth of Populus hybrids
during their first growing season on tilled
and untilled sites in lower Michigan,
(Dansville) . . . . . . . . . . . . . . . . 24

2.8 First-year survival and growth of three
Populus hybrids established with simazine
and diuron in lower Michigan, (Dansville) . . 25

2.9 The effect of simazine and diuron on sur-
vival and growth of Populus hybrids during
their first growing season on tilled and
untilled sites in lower Michigan,
(Manistee) . . . . . . . . . . . . . . . . . 27

2.10 First-year survival and height growth of
three Po ulus hybrids establishment with
simazine an diuron in lower Michigan,
(Manistee) . . . . . . . . . . . . . . . . . 28

Vi

TABLE ‘ PAGE

3.1 Parentage of Pepulus clones used in
nitrogen experiment. . . . . . . . . 37

3.2 The effect of simazine on total nitro-
gen, phosphorus and leader height growth
of Populus hybrids, at two dates during
the first growing seasons. . . . . . 38

3.3 The effect of simazine on total kjeldahl
nitrogen, leader height growth and suro
vival of four l-yr-old Populus hybrids . 40

4.1 Parentage of theP Populus clones used in
herbicide screening. . . . . . . . . . 48

4.2 Criteria used for whole plant and
leaf Visual scoring. . . . . . . 50

4.3 Analysis of variance for number of
leaves per plant, height, dry weight,
plant and leaf score four weeks after
the application of varying rates of
simazine and diuron to Populus clones
grown on sand culture in the greenhouse. 52

4.4 Whole plant and leaf visual scores per
plant four weeks after the application
of varying rates of simazine to 21
Populus clones grown on sand culture
in the greenhouse. . . . . . . . . . . . 53

4.5 Whole plant and leaf visual scores per
plant four weeks after the application
of varying rates of diuron to 21 Populus
clones grown on sand culture in the
greenhouse . . . . . . . . . . . . . . . 54

4.6 Relative total dry weight, four weeks
after the application of varying rates
of simazine to 21 Populus clones grown

in sand culture in the greenhouse. 55
4.7 Relative dry weight, four weeks after

the application of varying rates of

diuron to 21 Populus clones grown in

sand culture in the greenhouse . . . . . 56

vii

TABLE

4.8

5-3

5.4

5.5

5.6

Toxicity of simazine to 21 Populus
clones as shown by ED20 and ED5o
values. . . . . . . . .

Toxicity of diuron to 21 Populus
clones as shown by ED20 and .EDSO
values. . .

Clonal rankings based on ED values
for simazineand diuron four weeks
after treatment with varying levels of
the herbicides. . . . .

Leaf plastochron index (LPI) in relation
to leaf serial number and plastochron
index (PI) for young Poplars measured

at various times for response to simazine .

Physical condition of Populus clones NE
388 and NC 5328 two weeks after treatment
with; ' mg/pot simazine. . . . .

Abaxial leaf conductance of Populus
clones NE 388 and NC 5328 after treat-
ment with 5 mg,/pot simazine . .

C02 compensation concentrations of
Populus clones NE 388 and NC 5328
after treatment with 5 mg/pot simazine.

Leaf photosynthetic rate of Populus
clones NE 388 and NC 5328 after treat-
ment with5 mg/pot simazine . . . . .

Specific leaf weight of Popfl us clones

NE 388 and NC 5328 afte1 treatment with
5 mg/pot simazine .

viii

PAGE

61

62

63

78

80

81

83

84

LIST OF FIGURES

FIGURE PAGE

3.1

Effect of simazine on weed control

and survival of Populus clones at

the end of their first growing season

in lower Michigan (TRC). . . . . . . . 42.

Relative total dry weights of Populus

clones, four weeks after treatment

with varying rates of simazine and

diuron . . . . . . . . . . . . . . . . . . 5?

ix

CHAPTER I

INTRODUCTION

Among the hardwoods proposed for high-yielding,
intensive culture in the north-temperate regions of the
United States is the genus Populus, especially members of
sections Aigeiros (cottonwoods) and Tacamahaca (balsam
poplars) and their hybrids (Schreiner, 1970; Dickmann,
1975). Poplars are among the fastest-growing trees in
North America, they can easily be propagated vegetatively
by hardwood cuttings and coppice regeneration after har-
vesting is vigorous. However, poplars are "prime donnas"
(McKnight, 1970); their high yield potential can only be
realized on sites where moisture, aeration, and fertility
are adequate throughout the growing season. In addition,
a high level of silviculture, especially control of com-
peting vegetation, is required for the attainment of their
yield potential.

A number of attempts have been made to identify
the most suitable establishment methods for poplar (DeBell
and Alford, 1972; Briscoe, 1973; Randall and Kennedy, 1976;
Gilmore, 1976; Petersen and Phipps 1976; Randall and
Krinard, 1977). Some of these findings have become routine
practices in plantation establishment. However, economic

l

2

considerations and practicability for large plantations
have made a few of them unattractive. For example, Randall
and Krinard (1977) found that l-yr—old rooted cuttings
planted in l m deep holes provided an excellent alterna-
tive to shallow planting. The obvious biological advan—
tages of deep-planting long, rooted cuttings, however,

are often outweighed by nursery and planting costs. Sim-
ilarly, neither survival nor first-year growth of a group
of six Stoneville, Mississippi, cottonwood clones was im-
proved by angle planting or cutting the base of cuttings
diagonally (Randall and Kennedy, 1976). Survival of cotton-
wood seedings was higher when seedlings were planted in
auger holes as opposed to dibble plantings; however, as
Gilmore (1976) pointed out, each manager has to decide be-
tween the alternatives of lower survival but lower planting
cost, or high survival and higher planting costs.

Site improvement and reduction in competition have
also been investigated for poplars. Schreiner (1945a,
1945b) early demonstrated the inhibiting effects of sod
on the growth and development of hybrid poplar. A number
of approaches to weed control have been investigated. The
applicability of black polyelthylene mulch in establishing
plantations of hybrid poplar was compared with mechanical
cultivation during two dissimilar growing seasons (Bower-
sox and Ward, 1969). The results indicated that establish-
ment success with polyethylene can equal or exceed that of

mechanical Cultivation. However, in a season of prolonged

3

drought, polyelthylene film hindered the recharge of soil
moisture by light rainfall, nullifying the early growth
advantage of the mulched trees. The economics of this
technique, though not investigated, do not appear attrac—
tive.

Mechanical cultivation has been the most commonly-
used method of weed control and site improvement for poplar
(Meritt and Bramble, 1966; Bowersox and Ward, 1969; Baker
and Blackmcn, 1978; Krinard and Johnson, 1975; McKnight
and Biesterfeldt, 1969; Minckler and Woerheide, 1965;
McKnight, 1970). Kennedy (1975) demonstrated the need for
extreme care during cultivation of young cottonwood plan-
tations. Poor first-year cultivation due to improper ad-
justment of equipment, disking too close to young plants
or driving so fast as to cover the cuttings with soil re—
sulted in growth losses. There are also planting spacing
and economic limitations to mechanical cultivation.

Biological pest management remains relatively unin-
vestigated in forestry. The concept of one organism con-
trolling another was recognized by Darwin (1859). Cover
crops (Ford and Williamson, 1952) to control unwanted vege-
tation have proved unsatisfactory in establishing hybrid
poplars. Recent advances in allelopathic research may offer
future practical utility in the control of unwanted vege-
tation. A number of plant species have been shown to possess
allelochemics which are capable of reducing vegetation

(Stachon and Zimdahl, 1980; Toai and Linscolt, 1979; Stewart,

1975; Steenhagen and Zimdahl, 1979; Kelsey and Harrington,
1979; Funk 23 31., 1979; Lockerman and'Putnam, 1979; Buch-
anan gt $1., 1978; Fischer gt 31., 1978). More research
still needs to be done before the concept can be of pract-
ical utility. Using insects to control weeds in forestry
and agriculture has received very little attention (Ander-
son, 1977). The goal of this approach, based on sound
principles of population ecology, is not weed eradication
but reduction of a weed's abundance to economically or
aesthetically tolerable levels (Goeden, 1977). Limita-
tions to application of biological weed control, however,
exist. Breeding insects or biotic agents for species
specificity has not met with any appreciable success and
the problem of restricting the biotic agent from the pre-
ferred plants after the exhaustion of the undesired plants
remains a problem (Anderson, 1977).

Reduction of weeds to non-competitive levels con-
tinues to be the aim of weed research in agronomy and short-
retation intensive forestry where the objective is to max-
imize the growth potential of the crop on a particular site.
Chemicals remain the major economically and efficient method
of attaining this objective. A number of attempts have-been
made to identify suitable pre- and post-emergent herbicides'
for use in the establishment of poplar (Esau and Morgan,

1977; Shipman, 1974; Woessner, 1972).

5

Simazine (Dickmann g3 g1., 1978; Martin and Carter,
1966; Shipman, 1974), for example, has been shown to be
promising for weed control in poplar. However, field and
greenhouse observations of plant injury due to application
of simazine or other herbicides such as diuron at levels
adequate for acceptable weed control have been reported
for some clones of poplar on different soils (Bowersox
and Ward, 1969; Dickmann g3 g1., 1978; von Althen, 1979;
Esau and Morgan, 1977). The extent and mechanism of dif-
ferential tolerance in Populus hybrid clones to various
herbicides remains relatively uninvestigated (von Althen,
1979).

Soil and environmental factors are among the most
important determinants of the efficacy of herbicides. The
effect of tillage, pH, clay minerals and other textural
fractions, organic matter, nutrient types and levels, on
simazine have been investigated (Sheets, 1970; Weber, 1970;
Best g3 g1., 1975; Kells g3 gl., 1980; Koren and Shlevin,
1977; Atkinson and Allen, 1976; Hance, 1976; Slack g3 g1.,
1978; Nearpass, 1965; Hance g3 g1., 1968, 1977; Walker and
Thompson, 1977; Richardson and Banting, 1977). In a few
cases diuron was included in the investigations. In a
review on ways to influence the activity and persistence
of triazine herbicides in soils, LeBaron (1970) stressed
the complimentarity of some form of mechanical cultivation
and triazine herbicide application. This practice is wide-
spread in agronomy but is little known in intensive fores-

try (MCKnight, 1970).

Differential clonal responses to simazine and
diuron, and the interactive effect of soil factors on
both the efficacy of the herbicides and performance of
poplar clones call for specific site, clonal and chemical
evaluations. The potential contribution of tillage in
chemical control of weeds in intensive culture of poplar
also deserves investigation. Equally important is an un-
derstanding of the physiological mechanism of tolerance
of poplar to simazine and diuron.

The research reported in this dissertation inves-
tigated:

1. The effect of tillage, clone, herbicide
(simazine and diuron) and their interaction
on the establishment of poplar plantations
at different locations in lower Michigan. '

2. The influence of simazine on total nitrogen
concentrations in foliage of field-grown
poplar clones.

3. The dose-response of selected poplar clones
treated with varying rates of simazine or
diuron in the greenhouse using a sand culture
technique.

4. Variation in photosynthesis, leaf conductance
and leaf morphology of poplar clones identified

as tolerant or intolerant to simazine.

CHAPTER II

THE EFFECT OF TILLAGE, CLONE, HERBICIDE
(SIMAZINE AND DIURON) ON THE ESTABLISHMENT
OF POPLAR PLANTATIONS AT DIFFERENT LOCATIONS
IN LOWER MICHIGAN

INTRODUCTION

Residual activity of herbicides is essential for
season long control of weeds. Without residual activity,
frequent applications of less persistent herbicides would
be necessary, and costs of weed control would be high.
Simazine and diuron exhibit varying degrees of persist-
ence in soils. Rates of disappearance of these chemicals
are dependent on several environmental and edaphic factors
(Hartley, 1976; Muzik, 1976). Soil texture has a greater
effect on carry-over of several herbicides than climate
(Sheets, 1970), with carry-over greater in course than in
fine-textured soils (Harris and Sheets, 1965). The phyto-
toxicity of diuron was not influenced by soil pH of between
4.3 and 7.5 (Corbin g3 gl., 1971). But persistence and
adsorption of simazine by several soils was correlated
significantly with percent clay, organic matter and titrable
acidity (Nearpass, 1965). Persistence of simazine in the
soil was shown to increase with soil pH (Slack g1 gl., 1978),

14

while rate of formation of an unextractable C-breakdown

7

product from lI‘FC-atrazine increased with decreasing pH
(Kells g3 g1., 1980).

In field studies Best g3 gl., (1975) showed that
liming an acid Bladen silt loam which increased pH from
5.5 to 7.5, increased the phytotoxicity of several S-
triazines. In forestry, unlike agronomic situations where
carry—over could be a problem, the greater the persistence
of an herbicide, the greater its effectiveness in weed con-
trol.

Soil-type effects on persistence pg; gg are us-
ually difficult to assess from field experiments due to
the complicating influence of climate, especially rainfall
and temperature. While it is simple to show that persis-
tence varies among soils, determination of the causes for
differences is difficult in a crude soil system (LeBarron,
1970). It is essential, therefore, that information is
obtained for particular herbicides on specific sites in-
tended for intensive poplar culture.

On some soil types substituting herbicides for cul-
tivation is not only practical but may benefit some crops
by avoiding root damage (LeBarron, 1970). However, there
has been an increasing realization that the use of herbi-
cides and tillage often complement each other. Tillage in
combination with several herbicides has been shown to in-
crease both weed control and yield of soybeans over no-till

methods (Kapusta, 1979). Field studies on the persistence

of simazine showed less persistence under no-tillage corn
than conventionally-tilled corn (Slack g3 g1., 1978), and

14

the rate of formation of an unextractable C-compound

lu’C-atrazine was greater under no-tillage (Kells

from
g3 g1., 1980). Such information in forestry is lacking,
especially in intensive culture of poplar.

The purpose of this study was to investigate the
effect of tillage on the phytotoxicity of varying rates
of simazine and diuron during establishment of hardwood

cuttings of several different clones of hybrid poplar at

three sites in lower Michigan.

MATERIALS AND METHODS

The study sites were located in three areas in
lower Michigan. The first was at the Tree Research Center
(TRC) of Michigan State University (NEi X 6 T3N RIW) in
Ingham County; the second was also in Ingham County near
Dansville (S 33 T2N RlE), and the third was in Mason County
South of Manistee (S 25 T20N R17W). The three areas were
previously agricultural lands that had been abandoned in
the last 15 to 20 years and were occupied by grasses, and
broad-leaf weeds. Each of the 3 experiments was a split-
split-plct, three-level factorial. The three levels were
tillage, herbicide, and clone. Tillage in each experiment
was accomplished with an Oliver 550 tractor fitted with a

1.5 m wide tiller, run with the power take-off from the

lO

tractor. The tractor made two passes on each tilled area
to a depth of 15 cm. The herbicide was sprayed with a
tractor mounted, 323.0 liter tank with a rear pump also
run from the power take-off. The sprayer consisted.of 2
T-jet nozzles (#8006) 46 cm apart, delivering a spray
width of 90 cm. Tractor speed was maintained at 3.2 km/
hr and tank pressure was maintained at 2x106 dynes /cm2
for all spraying.

Cuttings were ca. 25 cm long and 1.3 cm in dia-
meter on the average and had buds close to the proximal
end. Cuttings were planted by hand with ca. 2.5 cm of
each cutting left above the soil surface. Triplicate soil
samples were taken randomly with a soil auger from each
planting site at the beginning of each experiment. Depth
to the B horizon was measured for each sample. Textural
analysis was done on the samples using the Bouyoucos (1951)
hydrometer method. Organic matter, pH and nutrient deter-
minations were done by the Michigan State University Soil
Testing Laboratory (Table 2.1).

All data collected were statistically evaluated
using the analysis of variance. Means were compared using
the least significant difference (LSD) at the 10% signi-

ficance level (Cochran and Cox, 1957).

ll

 

 

 

TABLE 2.1 SOIL PROPERTIES OF THE EXPERIMENTAL PLANTATION
SITES
Experimental Sites
Character Horizon TRQi Dansville Manistee
Soil Series -- Metea Belle Nester
Sandy Fontaine Loam
Loam Sandy
Loam
Texture
(Class) AP Sandy Loamy Sandy
Loam Sand Loam
A2 Loamy Loamy Loamy
Sand Sand Sand
Organic AP 7.0 3.2 4.0
Matter (%)
A2 2.8 1.4 1.6
Clay (9%) AP 15.0 8.0 11.5
A2 13.5 6.0 10.0
Nitrate AP 4.6 10.5 5.0
(mg/kg)
Depth (cm) AP 30 19 27
A2 17 18 17
PH AP 6.7 6.1 5.6
A2 7.4 7.1 6.1

 

12

TRC Plantation

This plantation was established in spring of 1978
on a 60 m x 60 m area and followed for 2 years. The area
was divided into 5 blocks of 60 m x 12 m each. Each block
was partitioned into parallel strips among which simazine
levels of O, 2, 3 and 4 kg/ha active ingredient (a.i.) were
randomly partitioned. Tilled and untilled factors were
alternatively imposed on each level of simazine. Glypho-
sate at a rate of 2 kg/ha a.i. was sprayed over the un-
tilled plots to control existing weeds a few days before
simazine was sprayed. The control plots were Sprayed only
with glyphosate and subsequent weed control was done with
a mower, repeated twice a month for the first year.

Twelve dormant hardwood cuttings of four Populus
clones, P. euramericana (NC 5323), P. "charkowiensisf x

P. "baudina" (H 47), P.

WXE-W
(NE 388), and P. maximowiczii x P. "berolinesis" (NE 48),
were randomized within each tillage factor (Table 2.2).
Cuttings were planted on May 27th, 8 days after the area

was sprayed with simazine, at a spacing of 1.5 m between
rows and 1.2 m between the trees within rows. Two border
trees on either end of each row were planted for each treat-
ment combination. There was no rain during the week of
planting; the days were sunny and temperatures were in the
high 80's. Percent survival was determined 5, 9 and 17

weeks after planting, and leader heights were measured 9

 

13

TABLE 2.2 PARENTAGE OF POPULUS CLONES PLANTED ON THE
THREE EXPERIMENTAL PLANTATION SITES.

 

 

Clone No. Parentage Section
NC 5323 Populus x euramericana Aigeiros
(Canada Blanc
NC 5328 Populus x eruamericana Aigeiros
(I 45751)
H 47 2. cv "charkowiensis" x Aigeiros
2. cv. "caudina"
NE 41 g. maximowiczii x g. Tacamahaca
trichocar a
(Androscoggin)
NE 388 2. maximowiczii x g. Tacamahaca
trichocar a
(Kingston)
NE 48 P. maximowiczii x P. Tacamahaca
cv. "berolinensis" x

Aigeiros

 

 

l4

and 17 weeks after planting. Weed control was assessed
visually at the end of the season before the first frost.
Early in the second growing season and twice a
month for the rest of the season the entire plantation
was mowed. Height and diameter 5 cm above ground level
were measured on July 25th and October 25th. The dry
weight of wood and bark of both leader and branches were
estimated from a regression based on diamter2 x height

(Gottschalk and Dickmann, 1980).

Dansville Plantation

This plantation was established in the spring of
1979 on a 36 m x 72 m area. Unlike the TRC plantation,
tillage was the first factor in the split-split plot
factorial experiment. Glyphosate at the rate of 2 kg/ha
a.i. was Sprayed over the untilled plots to control exis-
ting weeds. Simazine and diuron each at 2 and 4 kg/ha a.i.
plus a control were split over and randomized within each
tillage factor in parallel strips. The controls were mowed
twice a month for the entire growing period.

Three of the Populus clones used in the TRC plan-
tation (NC 5323, NE 388 and NE 48) were randomized within
each herbicide level and control (Table 2.2). Six dormant
hardwood cuttings of each clone were planted by hand at a
spacing of 2 m between rows and 2 m between each plant with-

in the row. Planting was done on May 26th, a cool cloudy

 

15

day, 8 days after the area was sprayed with simazine and
diuron. There were three replications. Percent survival
and leader height growth were determined 9 and 19 weeks
after planting. At the last sampling time, 2 randomly
selected trees were harvested from each clone for each
treatment combination and average weight of both leader

and branches was taken after drying at 75 C for 48 hr.

Manistee Plantation

 

This plantation was established in the spring of
1979 on a 78 m x 60 m area. Tillage was the first factor
here as in the Dansville plantation. However, unlike the
other plantations, the entire area was tilled once in the
fall of 1978. In May, 1979, a second tillage was imposed.
A 78 m x 10 m strip was tilled and alternated with an un-
tilled 78 m x 10 m strip in each block. Glyphosate at the
rate of 2 kg/ha a.i. was sprayed over the untilled plots
to control existing vegetation. Simazine anddiuron each
at 2 kg/ha a.i. plus a control were sprayed in parallel
strips and randomized within each tillage factor.

Nine dormant hardwood cuttings of three Populus
clones, NC 5323, P. x euramericana (NC 5328) and g.
maximowiczii x p. trichocarpa (NE 41) were planted ran-
domly within each herbicide level and the control at a
spacing of 3 m within rows and 2 m between rows (Table
2.2). Simazine and diuron were Sprayed separately over

the planted cuttings on June 14th, 15 days after planting.

16
The control was left unweeded for the duration of the ex-
periment. There were 3 replications. Survival and leader
height growth determinations were done 11 and 19 weeks
after planting. Biomass of wood and bark was determined

as for the Dansville plantation.

RESULTS

TRC YEAR ONE

There were generally no significant differences
in survival or height growth among the rates of simazine
throughout the season (Table 2.3), although highest rates
of simazine tended to reduce survival. However, survival
in the weed-free controls was significantly better than
in plots treated with highest levels of simazine. Height
growth in control plots was significantly higher than height
growth at 4 kg/ha simazine but not different from that at
2 and 3 kg/ha at the middle and end of season. Weed con-
trol at 4 kg/ha simazine was comparable to the weed-free
control but higher than at 2 and 3 kg/ha (Table 2.3). Weed
control at 2 and 3 kg/ha simazine did not differ.

There were significant differences in survival and
growth between tilled and untilled sites (Table 2.3), with
survival and height at the end of the season about 20% and
30 cm better on the tilled compared with the untilled sites.
Weed control was also slightly better on tilled sites. The

effect of different rates of simazine remained the same on

l7

 

 

 

 

 

 

TABLE 2.3 THE EFFECT OF SIMAZINE 0N SURVIVAL AND HEIGHT

GROWTH OF POPULUS HYBRIDS IN THEIR FIRST GROWING

SEASON 0N TILLED AND UNTILLED SITES IN LOWER

MICHIGAN, (TRC).

Weeks After Planting
17
Till- Simazine Surv Surv Ht Surv. Ht Weed
age (ks/ha (7o) (75) (cm) (%) (cm) Control
a.1. ____ ____ ____ (fil____

Tilled 0 88 81 36 81 97 94

2 76 69 32 68 91 80

3 70 65 31 65 89 72

4 62 52 31 52 78 86
Untilled O 71 58 21 57 62 91

2 67 43 17 42 56 74

3 71 46 18 45 61 71

4 60 37 17 35 49 88

LSD .10 13 16 5 16 14 8

 

 

18

either the tilled or untilled sites (Table 2.3). However,
simazine and tillage supplemented each other and signi-
ficantly increased end-of—season survival and growth of
plants by over 15% and 20%, respectively, above either
tillage or simazine alone.

There were significant clonal differences in sur—
vival and growth (Table 2.4), with clones NC 5323 and H 47
surviving better at 5, 9 and 17 weeks after planting com-
pared to clones NE 388 and NE 48. There were generally
no differences in survival between each clonal pair. At
the middle of the season, 9 weeks after planting, the
ranking in height among the four clones was H 47 , NC 5323 ,
NE 48 ,NE 388. There were no significant differences
in height among clones at the end of the season. Clones
NC 5323 and H 47 had better survival at all rates of sim-
azine tested than clones NE 48 and NE 388 at the middle
and the end of season (Table 2.4). There were also signi-
ficant differences in height growth within some simazine
rates. H 47 grew best at 4 kg/ha whereas NE 388 was the
most inhibited at this herbicide rate. At the end of the
first season there were no significant differences in

height among clones at 2 kg/ha simazine.

l9

TABLE 2.4 FIRST-YEAR SURVIVAL AND HEIGHT GROWTH OF FOUR
POPULUS HYBRIDS ESTABLISHED WITH VARYING LEVELS

OF SIMAZINE IN LOWER MICHIGAN,

(TRC).

 

Simazine
k ha a.i.

O

mire.
No 5323
H 47

NE 388
NE 48

NC 5323
H 47

NE 388
NE 48

NC 5323
H 47

NE 388
NE 48

NC 5323
H 47

NE 388
NE 48
LSD.10

Weeks After Planting

 

Surv

81
88
80
68

81
79
61
65

73
75
64
69

65
76
51
53
12

 

77 29 76 79
74 32 72 75
64 25 66 83
63 26 63 78
61 23 61 7O
68 33 66 77
44 21 43 73
51 21 51 73
63 25 63 71
60 25 58 66
48 23 46 82
53 24 52 78
45 22 43 59
57 28 55 70
36 19 33 58
no 2a 41 65
14 3 14 11

 

20
TRC YEAR TWO:

The significant differences in growth due to the
different rates of simazine carried over into the second
year (Table 2.5). Survival at the end of the first year
compared to survival the second year within each simazine
rate were not significantly different. Trends in survival
among different rates of simazine were also the same as
for the first year. Height, diameter and biomass at the
middle and end of season were significantly lower at 4 kg/
ha simazine compared to the control. Differences among the
lower rates of simazine and the control were not significant.
At the end of the season control plants were taller and
greater in diameter than plants in the 2 and 3 kg/ha sima-
zine plots, although biomass was not significantly differ-
ent. There were no significant differences in growth and
biomass production between 2 and 3 kg/ha simazine. Growth
and biomass yield were again better on the tilled compared
to the untilled sites at the middle and end of the season
(Table 2.5).

Survival patterns among clones the second year were
not significantly different from the first year (Table 2.6).
Growth and biomass yield of clones NC 5323 and H 47 were
better than NE 388 and NE 48 at the middle and end of season.
There were no significant differences in growth between
NC 5323 and H 47, but height at the middle and end of sea-
son and diameter at the end of season were lower in NE 48

compared to NE 388.

21

 

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22

 

 

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23
Eansxills

In general, survival was very low on this site.
Simazine at the two rates investigated caused less mor-
tality than diuron, while the weed-free control tended
to have higher survival and height growth at the middle
and end of season compared to the herbicide treatments.
End-of-season tree biomass was not significantly differ-
ent among herbicide treatments and the control, although
biomass was reduced at highest herbicide levels (Table
2.7).

Survival and growth were more than 50% better on
the tilled compared with the untilled sites at both periods
of measurement (Table 2.7). Biomass of wood and bark at
the end of the season was about 300% better on the tilled
sites. Plants in the simazine and diuron treated plots
survived and grew better when the site was tilled (Table
2.7). Survival and growth on tilled sites at each herbi-
cide level were significantly better than either herbicide
or tillage alone, although the trend in growth and biomass
yield with herbicide and herbicide rate was still the same.

There were clonal differences in survival, height
growth and biomass yield on this site (Table 2.8). NC 5323
had the highest while NE 388 was poorest. The height and
biomass of NC 5323 and NE 48 were not significantly dif-
ferent but higher than NE 388 at the middle and end of the

season. The ranking of the clones with respect to survival

24

TABLE 2.? THE EFFECT OF SIMAZINE AND DIURON 0N SURVIVAL
AND HEIGHT GROWTH OF POPULUS HYBRIDS DURING
THEIR GROWING SEASON 0N TILLED AND UNTILLED
SITES IN LOWER MICHIGAN, (DANSVILLE).

 

Period of Measurement

 

 

Herbicide Mid-Season End of Season
Tillage Type Rate Surv Ht Surv Ht Wood &
(ks/ha (%) (cm) (93) (cm)Bark
a.i. (g)
Tilled Control 0 65 25 61 31 3.5
Simazine 2 46 21 44 40 3.5
4 5o 22 50 34 4.3
Diuron 2 43 24 41 37 5 .0
4 22 ll 17 17 2.2
Untilled Control 0 35 14 30 16 1.2
Simazine 2 30 9 24 19 1.2
4 ll 6 7 12 0.8
Diuron 2 19 7 15 10 0.5
4 13 5 6 10 0.6

LSD.10 l7 8 13 9 2.0

 

 

25

TABLE 2.8 FIRST-YEAR SURVIVAL AND GROWTH OF THREE POPULUS
HYBRIDS ESTABLISHED WITH SIMAZINE AND DIURON
IN LOWER MICHIGAN, (DANSVILLE).

 

Period of Measurement

Mid-Season End of Season

 

 

 

 

 

 

Type Rate Clone Surv Ht Surv Ht Wood &
gingham (%) (cm) (7») (cm) Bark
Control 0 NC'5323 ' 75 17 7O 21 1.7
NE 48 47 22 39 26 2.1
NE 388 28 20 28 23 3.2
Simazine 2 NC 5323 70 16 58 33 2.6
NE 48 33 16 33 30 2.6
NE 388 ll 14 11 24 2.0
4 NC 5323 53 14 53 28 2.0
NE 48 25 20 25 26 4.6
NE 388 14 8 8 14 1.0
Diuron 2 NC 5323 47 20 42 29 5.0
NE 48 25 16 25 24 2.0
NE 388 20 11 17 18 1.3
4 NC 5323 36 17 22 29 3.2
NE 38 17 8 ll 12 1.0
NE 388 O O O O 0.0
LSD 10 17 7 l7 l3 2

 

26
and growth were unaffected by the different levels of both
simazine and diuron at both periods of measurement (Table
2.8). NC 5323 showed the best performance at any herbi-

cide rate while NE 388 was the poorest.

Manistee

In general, all herbicide treatments showed better
survival and growth than the unweeded controls (Table 2.9).
Survival and growth of plants on diuron-treated areas were
better than on simazine-treated areas. There were no signi-
ficant differences in survival and growth of plants among
rates within each herbicide. The trend in herbicide ef-
ficacy remained the same on tilled versus untilled sites
(Table 2.9). Survival and growth were significantly higher
on tilled compared with untilled sites at each herbicide
rate tested. Survival and growth of plants at different
rates of diuron were significantly better than at differ-
ent rates of simazine on either tilled or untilled sites.
Survival and growth in a tillage-herbicide combination were
better than either alone.

There were significant clonal differences in sur-
vival, height growth and biomass yield (Table 2.10). Clone
NC 5323 had better survival compared with NE 41 and NC 5328
at the middle and end of season. Height growth of NE 41
was higher than NC 5328 or NC 5323 at the two periods of
measurement. Biomass yield of NE 41 was also higher than

NC 5323 and NC 5328. The trends in clonal and herbicidal

27

TABLE 2.9 THE EFFECT OF SIMAZINE AND DIURON 0N SURVIVAL
AND GROWTH OF POPULUS HYBRIDS DURING THEIR
FIRST GROWING SEASON ON TILLED AND UNTILLED
SITES IN LOWER MICHIGAN, (MANISTEE).

 

Treatment

Herbicide

Tillage Type

Tilled Controla

Simazine

Diuron

Untilled Controla

Simazine

Diuron

LSD.10

Rate
(kg/ha
a.i.)

c- n: -: A) c:

.p N e- A) c3

Period of Measurement

Mid-Season End_of Season
Surv Ht Surv Ht Wood &
(%) (cm) (%) (cm) Bark

8

 

 

42 26 39 30 1.6
68 31 60 43 5.7
60 33 57 45 5.5
77 37 77 56 13.3
68 41 67 72 16.6
40 26 38 38 5.2
41 26 36 40 5.0
43 23 40 33 2.4
57 28 54 50 5.1
56 24 49 44 5.0
18 7 l7 l5 8

 

aUnweeded Control

28

TABLE 2.10 FIRST-YEAR SURVIVAL AND HEIGHT GROWTH OF THREE
POPULUS HYBRIDS ESTABLISHED WITH SIMAZINE AND
DIURON IN LOWER MICHIGAN, (MANISTEE).

 

Period of Measurement

 

 

 

 

 

 

 

Herbicides Mid-Season End of Season
Type Rate Clone Surv Ht Surv Ht Wood &
(kg/ha (%) (cm) (%) (cm) Bark
a.i.) ____. .____ (g)
Controla 0 NC 5323 62 26 62 38 2.2
NE 41 48 35 42 45 6.7
NC 5328 13 17 12 19 1.3
Simazine 2 NC 5323 72 28 66 39 5.1
NE 41 56 34 43 47 5.7
NC 5328 36 23 34 38 5.2
4 NC 5323 72 28 68 43 4.0
NE 41 45 32 44 43 3.0
NC 5328 38 23 33 31 4-8
Diuron 2 NC 5323 72 33 74 56 7.5
NE 41 68 34 66 55 10.9
NC 5328 60 31 57 49 9.4
4 NC 5323 58 32 56 62 11.0
NE 41 74 44 7o 78 16.2
NC 5328 54 21 48 34 6.7
LSD.10 24 ll 24 21 5

 

aUnweeded Control

29
behavior were still essentially the same as in the main
effects (Table 2.10). NE 41 performed.best with regards
to biomass production at all herbicide rates except at
4 kg/ha simazine. NC 5328 showed poorest survival and
height at all herbicide rates. Survival and growth of
the clones were better at various levels of diuron com-

pared to simazine or the unweeded control.

DISCUSSION

In these experiments the successful establishment
of unrooted poplar cuttings was influenced significantly
by the type and rate of herbicide applied, whether or not
the area was tilled and the clone used. The persistence
of simazine is influenced by both tillage and pH of the
soil. Kapusta (1979) showed that persistence of simazine
was increased by tillage, while Slack g3 g1., (1978) demon-
strated that simazine persistence was lowest on soils of
pH 5.4 or less. Corbin g: g;, (1971) reported highest
activity of triazines at pH 6.5 and that soil pH levels
between 4.3 and 7.5 had no effect on phytotoxicity of diuron.
In general the data presented here are in agreement
with these reports. The Ap horizon had a pH of 6.7 at the
TRC and 6.1 at Dansville but only 5.6 at Manistee (Table 2.1).
Simazine at 2 or 3 kg/ha at the TRC and 2 kg/ha at Dansville
was adequate for establishment of poplar cuttings on either

tilled or untilled sites. At Manistee, however, simazine

30

at both rates was ineffective, probably due to the low pH
of the surface soil. The effect of surface soil pH and
tillage is similar. Kells g3 gl. (1980) found that rate

14

of formation of an unextractable C-compound from soil

treated with 1“

C-atrazine was greater under no tillage
and increased with decreasing pH. The effect of tillage
in increasing persistence of simazine may be through its
effects on the pH of the soil, since organic matter in-
corporation during tillage has the potential of making
the soil less acidic. The use of lime to raise soil pH
at the Manistee site may be a practical way to make this
soil suitable for simazine use (Kells ggpgl., 1980).

On each of the three plantation sites, weed control
was 70% or better at any herbicide rate on tilled or un-
tilled plots except at Manistee where weed control on
simazine treated plots was less than 50% at the end of the
first growing season. In general, weed species were ef-
fectively controlled at TRC and Dansville; however, at
Manistee, witchgrass (Panicum capillare) formed a dense mat
on simazine-treated plots, irrespective of the rate. Diuron
on the other hand, controlled witchgrass. The reduction in
survival and growth of ngglgg trees on simazine treated
plots at Manistee plantation was probably due to the pres-
ence of this resistant weed species in addition to the re-
duced activity of simazine due to the low pH of the surface

soil.

31

The single initial tillage operation at the begin-
ning of the season benefitted all clones tested at all her-
bicide rates. Survival, growth and biomass yield were
higher on tilled than untilled plots. Supplementing till-
age with herbicides further increased survival and growth
of the clones above what was obtained with tillage or her-
bicide alone. The increased performance of the clones with
tillage might be due to increased persistence of herbi-
cides on tilled plots (Slack gt g1., 1978). The enhance-
ment of tree establishment due to increased moisture and
soil contact with the planted cuttings probably was also
a contributing factor. Grazing on young shoots by insects
and animals present under the dead but standing weeds was
also a problem for the poplar trees and may contribute to
the low survival on the untilled sites.

On the three sites there were clonal differences
in survival, height, diameter and biomass. Clones from
section Aigeiros generally survived better than clones from
section Tacamahaca at all herbicide rates. Tacamahaca clones
grew well, however, often better than the Aigeiros clones
probably because of their greater leaf area duration (Dick-
mann, 1979). NC 5323 and H 47, for example, set bud in late
August whereas NE 48 and NE 388 set bud in late September.
These clonal differences have important implications in sel-
ection.or breeding of clones for use in intensive plantation
establishment. Clones with high survival and growth rate

are preferred; however, a trade-off might be made between

32

clones with high survival but less growth and clones with
less survival but high growth rates. An understanding of
the factors affecting survival of Populus hybrids will
enhance the managers' ability to make the best choice of
clones intended for plantations.

Differential clonal response to simazine and diuron
occurred at the three study areas. Higher doses of each
herbicide were more toxic to each of the clones tested.

At the TRC 4 kg/ha a.i. simazine caused high-mortality and
growth inhibition in all clones, but this effect was more
severe in Tacamahaca clones NE 388 and NE 48. Simazine at

2 kg/ha a.i. appeared suitable for all clones tested at the
TRC, although survival was still higher for NC 5323 and H 47.
Productivity of each clone at the high rate of simazine in
the second year was still significantly low probably due to
the "compound-interest" nature of growth. At Dansville 2 kg/
ha a.i. of simazine or diuron would be a suitable applica~
tion for all clones tested. At Manistee diuron offered the
best potential for use with any of the clones tested. Al-
though differential clonal response would still occur, for
economic reasons 2 kg/ha a.i. diuron would be preferred.
Differential clonal response to herbicides has been reported
among Populus hybrids (von Althen, 1979; Dickmann g3 g1.,
1978), although the exact reasons are not known. In these
experiments, however, it appeared that clones with high es-
tablishment qualities, exemplified in percent survival,

were little affected by simazine or diuron at rates adequate

33

for effective weed control. This high surviving ability
would probably be in addition to any physiological, bio-
chemical or morphological basis for differential toler-

ance that might exist in the clones.

CHAPTER III

THE EFFECT OF SIMAZINE 0N TOTAL
FOLIAR NITROGEN AND PHOSPHORUS CONTENT
OF FIELD-GROWN HYBRID POPULUS

W

The stimulatory effect of simazine at subtoxic
levels on plant growth and nitrogen nutrition has been
reported extensively in crop plants (Ries, 1976; Ebert
and Dumford, 1976). Bartley (1957) made one of the first
observations that simazine may improve growth, noting that
corn was greener and taller when simazine was applied at
rates up to 18 kg/ha. Later works have shown similar re-
sponses for apple and peach trees, certain conifers and
oak trees (Ries g§_gl., 1963; Conner and White, 1968; Ries,
1976). Ten kg/ha of simazine has been estimated to pro-
duce a response in apples equivalent to an application of
200 to 250 kg/ha of nitrogen fertilizer (Karnatz, 1964
as cited in Ries, 1976). However, in several cases no
effect on dry matter was observed or additional height
growth was offset by a reduction in plant dry weight
(Tweedy g3 g1., 1971; Ries, 1976; Ebert and Dumford,
1976). Simazine applied preemergence at herbicidal rates

to field planted Scotch pine, white spruce and balsam fir,

34

35

however, did not significantly alter their foliar nitrogen
concentration (Conner and White, 1968).

Ries gipgl. (1963) was one of the first to sug-
gest that simazine may be involved in the alteration of
nitrogen nutrition of plants. Since then several inves-
tigations on the mechanism of simazine stimulation of
protein synthesis have been reported (Ries and Wert, 1972;
Dell and Meggitt, 1968; Pulver and Ries, 1973; Tweedy and
Ries, 1967; Tweedy gt g_l_., 1971; Lund-Hoeie, I969b). Stim-
ulation of root growth by subherbicidal levels of tri-
azines was reported for conifers (Lund-Hoeie, 1969b).
Freney, (1965) suggested that simazine increased plant
growth by a direct effect on plant metabolism and not by
an interaction with the soil because he could find no
simazine effect on mineralization of soil organic nitro-
gen. It has also been reported that nitrogen content
would increase in corn after triazine treatment only when
the temperature was low, but when nitrate was replaced by
ammonium ion in the nutrient cultures, no extra stimula-
tion of nitrogen uptake occurred (Tweedy and Ries, 1967;
D011 and Meggit, 1968). While it has been demonstrated
that hill reaction inhibitors like the triazines increase
protein synthesis which induces more rapid nitrate uptake
in plants, the mechanism of such action is not clear.

In the intensive culture of Poplar, simazine is
one herbicide that can be used to suppress weed competition

during plantation establishment (Dickmann g3 g1., 1978;

36

von Althen, 1979). An understanding of the effect of
simazine on survival, growth and leaf nutrient content,
especially total nitrogen, of hybrid Populus clones will
enhance the selection of proper weed control strategies
or the breeding of new clones. The study reported here
was conducted to evaluate the effect of varying rates of
soil-applied simazine on concentrations of total foliar

nitrogen and phosphorus in four field-grown Populus hybrids.

MATERIALS AND METHODS

The experimental site was a tilled old-field area
on the Michigan State University campus in East Lansing,
Michigan. The soil was of sandy-loam texture and contained
4.6 mg/g of N03 - N and 7% organic matter. Three simazine
rates (2,3 and 4 kg/ha a.i.) prepared from an 80% wettable
powder formulation, plus a control were randomly applied
in l m strips on the tilled area. The herbicide was sprayed
with a tractor-mounted aggitated tank sprayer on May 19,
1978. The unsprayed control strips were treated with 2 kg/
ha glyphosate prior to planting and then mechanically weeded
twice a month throughout the growing season.

Twelve dormant hardwood cuttings (25 cm long) of four

Pepulus clones (Table 3.1) were randomly planted within each

herbicide level in a Split-split-plot factorial design..

37

TABLE 3.1 PARENTAGE 0F POPULUS CLONES USED IN THIS EX-

 

 

 

 

 

 

PERIMENT.
Clone No. Hybrid Parentage g§ection
NC 5323 Populus x euramericana cv. Aigeiros
"Canada blanc"
H 47 P. cv. "Charkowiensig" x Aigeiros
g. cv. "caudina"
NE 388 g. maximowiczii x P. tri- Tacamahaca
chocarpa cv. "Kingston"
NE 48 E. maximowiczii x 3. cv. Tacamahaca
"berolinensis" x

Aigeires

Spacing was 3.0 m between rows and 1.2 m between trees
within a row. Planting was done by hand on May 27, 1978.
Each treatment combination was replicated five times.
Percent survival was determined and leader height
growth measured at intervals during the growing season.
Percent weed control was estimated visually at the end of
the season. Two mature leaves from each of ten trees per
clone, two trees from each replication, were harvested at
the middle and end of the growing season for each treat-
ment combination. The leaves from each treatment were com-
posited, dried at 70 C for 48 hr. and ground with a Wiley
mill. Digestion of dried leaf material was done with a
Tecator digestion system Model DS-40. Percent total (Kjel-
dahl) nitrogen and phosphorus were simultaneously deter-

mined using the Techniccn Auto Analyzer II system. All

38

data were subjected to analysis of variance and means were
compared at the 0.1 level of probability using the LSD
(Cochran and Cox, 1957).

RESULT AND DISCUSSION

Simazine had a significant effect on total foliar
nitrogen and leader height growth of hybrid Populus clones
at the middle of the growing season (Table 3.2). Foliage
samples at all simazine levels tested had significantly
higher total nitrogen than the weed-free control. Dif-
ferences among the simazine rates were not statistically
significant. However, height growth was reduced by sima-

zine treatment except at the 2 kg/ha a.i.

 

TABLE 3.2 THE EFFECT OF SIMAZINE ON TOTAL NITROGEN,
PHOSPHORUS AND LEADER HEIGHT GROWTH OF POPULUS
HYBRIDS, AT TWO DATES DURING THE FIRST GROWING

 

 

 

SEASON.
July 30 October 1

Simazine N P Ht N P Ht
Ez____1<haa.i. mmmmmm

O 3.0 .18 36 3.0 .19 97

2 3.3 .18 32 3.0 .20 91

3 3.3 .18 31 3.0 .20 89

4 3.2 .18 31 3.0 .20 78
LSD.1O .l .01 5 .2 .02 8

39

The end-of-season total nitrogen data showed no
significant differences between control and simazine treat-
ments, or among the different simazine rates (Table 3.2).
Heights at the same period were again statistically higher
for control plants than for those treated with the heaviest
levels of simazine. The slightly higher seasonal height
growth of control plants versus those treated with 2 kg/ha
a.i. simazine was probably due to an early-season growth
advantage of the control plants. The non-significant dif-
ference in foliar nitrogen at the end of the season indi-
cates the transient nature of the simazine effect. Apple
leaves also showed increased in nitrogen early in the
growing season after simazine applications but the effect
was diminished by June (Solecka g3 gl., 1969).

Simazine had no significant effect on total phos-
phorus of any clone at the two periods of sampling. Phos-
phorus levels were similar to those reported for other field-
grown Populus plants. (Blackmon and White, 1972; Einspahr,
1971).

There were significant differences among clones
in the extent to which foliar nitrogen accumulation was
stimulated by simazine (Table 3.3). Compared with the
weed-free control, clone NC 5323 treated with 3 kg/ha
simazine had significantly higher total foliar nitrogen
at the middle of the season, while clone H 47 treated with
2 kg/ha simazine showed significantly higher total foliar

nitrogen at the middle and end of season. Total foliar

40

TABLE 3.3 THE EFFECT OF SIMAZINE ON TOTAL KJELDAHL NITROGEN,
LEADER HEIGHT, GROWTH AND SURVIVAL OF FOUR l-YR-
OLD POPULUS HYBRIDS

 

Date of Sagpling

July 30 October 1
Clone Simazine N Ht Surv N Ht Surv

(Ks/ha a-i-) (%) (cm) (%) (%) (cm) (%)

 

NC 5323 0 3.2 36 90 3.2 95 88
2 3.2 29 85 3.3 87 85

3 3.6 33 67 3.1 91 67

4 3.3 30 48 3.2 77 48

H 47 0 3.5 42 80 3.1 94 78
2 3.9 46 93 3.5 97 90

3 3.8 33 71 3-3 84 72

4 3.7 33 70 3-5 83 70

NE 388 0 2.8 34 83 2.9 104 83
2 3.1 26 40 2.9 92 40

3 3.0 27 57 2.8 88 52

4 2.8 25 43 2.7 70 42

NE 48 0 2.7 33 72 3.0 95 71
2 2.9 29 56 2.5 89 57

3 2.9 31 67 2.9 93 67

4 3.0 34 45 2.7 81 45

LSD .10 .4 8 20 .4 20 19

 

41

nitrogen of H 47 was also higher than controls at the high—
est simazine rates, but height growth was suppressed.

At the other extreme, the nitrogen content of NE
388 appeared to be unaffected by simazine treatment at all
rates tested at the middle and end of the growing season.
Height growth of NE 388 at all simazine rates was lower
than the control, but there were no significant differ-
ences in height among the different herbicide rates. The
height growth response of NE 388 is probably an inhibitory
effect of simazine since this clone has been shown to be
very sensitive to this herbicide (von Althen, 1979; Chapter
2). Total foliar nitrogen and height growth of clone NE
48 was unaffected at both sampling periods by simazine
(Table 3.3).

Survival among the four clones was generally lower
in simazine-treated plots than in control plots (Table 3.3).
Clone H 47 exhibited highest survival, whereas clone NE 388
showed the least survival, at all rates of simazine tested.
Overall survival and weed control at the end of the season
for the 2 and 3 kg/ha rates of simazine represented an ac-
ceptable performance on this sandy-loam soil. (Figure 3.1).

These data suggest that untreated plants in the
weed-free control might actually be more efficient in ni-
trogen utilization; i.e., a simazine—induced increase in
nitrogen content does not necessarily produce correspond-
ingly greater growth. Simazine appeared to reduce nitrogen

efficiency in clones NC 5323, NE 388 and NE 48 but not in

42

FIGURE 3.1 EFFECT OF SIMAZINE ON WEED CONTROL AND
SURVIVAL OF POPULUS CLONES AT THE END OF
THEIR FIRST GROWING SEASON IN LOWER
MICHIGAN (TRC).

43

100
Weed Control

90 Survival

7

' ,,’

lPERC EN
0|
0

20

1o

 

O 2 3 4
SIMAZINE RATE [Kg/ha a.i.l

Figure 3.1

44

H 47. Apparently the potential stimulatory effect of higher
nitrogen levels is offset by the phytotoxic effects of
simazine on sensitive poplar clones.

The practical utility of nitrogen stimulation by
the triazines in agronomic or tree crops is elusive (Ries,
1976); however, any additional growth in a tree crop even-
tually shortens the length of the rotation, a definite
economic advantage. The direct exploitation of this phen-
omenon in tree breeding may be still far in the future,
however, owing to the problem of elucidating the mechanism
of such simazine stimulation of nitrogen uptake (Ebert and
Dumford, 1976). Screening, with a view to selecting clones
of Populus exhibiting total nitrogen stimulation by sima—
zine coupled with undiminished height growth and accept-
able survival, as in H 47 and NC 5323, will be of immed-
iate practical utility in selection of plant material for

high-yielding plantations.

CHAPTER IV

DIFFERENTIAL TOLERANCE 0F POPULUS
CLONES TO SIMAZINE AND DIURON

INTRODUCTION

Simazine (2-chloro-4, 6-bis (ethylamino) - s -
triazine) and diuron (3-(3,4-dichloropheny1) - 1, l-di-
methyl urea) have the potential to be economical forms of
weed control in poplar plantations due to their proven
ability to control weed competition and their ease of ap-
plication (von Althen, 1979; Dickmann g3 g1., 1978; Chapter
2). The greatest disadvantage of these chemicals is the
susceptibility of many poplar species and clones to dosage
necessary for effective weed control (von Althen, 1979;
Chapter 2). Little quantitative data is available, how-
ever, on the susceptibility of various peplar species and
clones to simazine and diuron. In a field experiment von
Althen (1979) showed that the Euramerican p0plar clone
I-45/51 was very tolerant to simazine up to 4.5 kg/ha in
two consecutive years of application. He also demonstrated
that other poplar clones exhibit a wide variance in toler-
ance to simazine in the field. In Chapter 2, it was re-

ported that NC 5323 was relatively tolerant while NE 388

45

46

was intolerant to simazine and diuron at several differ-
ent plantation sites in lower Michigan.

It has been demonstrated that the phytotoxicity
of simazine and diuron are affected by percent clay, or-
ganic matter and soil pH (Slack g3,gl., 1978; Kells
gt gl_. , 1980 ). Corbin g1; gl_. (1971) showed that phyto-
toxicity of the s-triazine prometone increased as soil
pH increased, reaching a maximum at pH 6.5, while soil
pH levels between 4.3 and 7.5 had no effect on the phyto-
toxicity of diuron. The differential phytotoxicity of
simazine and diuron due to soil pH was also reported in
Chapter 2; on the Manistee site where pH was 5.6 simazine
was ineffective while diuron was still effective in con-
trolling competiting vegetation. These herbicide-soil
interactions impose a severe limitation on the use of field
soils for the evaluations of relative tolerance of poplar
to simazine and diuron.

The purpose of this eXperiment was to investigate
the relative tolerance of 21 different Populus clones to
varying rates of simazine and diuron in the greenhouse
using a sand-culture technique modified from Clay and
Davison (1978). It was reasoned that this approach would
obviate some of the drawbacks inherent in field tolerance

trials.

47
MATERIALS AND METHODS

The screening experiment was conducted in a green-
house between June, 1979 and June 1980. Washed sand of
pH 7.5-8.0 was used to fill specially prepared 0.03 m3
plastic pots. The four holes at the base of each plastic
pot were sealed with screen mesh and fibre wool to prevent
the leaching of sand but still allow for free drainage and
aeration. The top 2.5 cm of each pot was left unfilled.

Dormant hardwood cuttings 30 cm in length and about
2.0 cm in diameter were made from one-year-old stool shoots.
Twenty-one clones of Populus species and hybrids were used
in the screening (Table 4.1). Selection of clones re-
flected the genetic diversity of the genus and included
representatives of sections Aigeiros, Tacamahaca and in-
tersectional crosses between them.

Simazine (Princep 80W) and diuron (Karmex 80WP)
were used in the screening. Each herbicide was applied
at five dose levels (1, 5, 10, 20 and 50 mg per pot) in
1 litre of water. Selection of the dose levels for both
herbicides was based on a preliminary experiment. There
was an untreated control for each herbicide. Replication
was at least two times, giving a minimum total of twelve
trees per clone for each herbicide. Evaluation of clones
NE 388 and NC 5328 were repeated at two separate occasions.

The eXperimental design was asplit-split-plot factorial.

48

TABLE 4.1 PARENTAGE OF THE POPULUS CLONES USED IN HERBICIDE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCREENING
glone Number Section Tacamahaca

NE 41 P. maximowiczii x 3. trichocarpa

NE 388 P. maximowiczii x P. trichocarpa

NC 5260 P. tr1stis x 3. balsamifera
Section Tacamahaca x Aigeiros

NE 48 g. maximowiczii x g. "berolinensis"

NE 298 P. "betulifolia" x.£. trichocagpa'

NE 302 P. "betulifolia" x g. trichocarpa

NE 207 g. deltoideg x P. trichocarpa

Jac 4 P. balsamifera x P. deltoides

Jac 7 P. balsamifera xpg. deltdideg

NE 218 g. deltoides x P. trichocarpa

Sgctign Aigeiros

NC 5323 g. x euramericana "Canada blanc"

NC 5326 P. x euramericana "Eugenei" ‘

NC 5328 g. x euramericana "I 45/51“

NC 5377 P. x euramericana "Wisconsin #5"

H 47 P. x "charkOWIensis" x g. "caudina"

NE 353 g. deltoides x 2. "caudina“

NE 308 P. "charkowiensis" x P. "incrassata"

NE 17 g. "charkowiensis" x g. "caudina"

NE 58 P. "rasumowskyana" x 3. "incrassata"

PD 184 g. deltoides '

PD 222 P. deltoides

 

 

49

Trees were about four weeks old before a single
application of herbicide directly to the surface of the
sand was made. The four weeks allowed the trees to es-
tablish in the pots and hence eliminated the comfounding
effect of inherent differences in clonal rooting and sur-
vival. When watering was necessary 1 litre of nutrient
solution was added rapidly to the sand surface; this was
sufficient to flood the pot and aerate the sand (Clay and
Davison, 1978). The nutrient solution was prepared from
a commercial water-soluble fertilizer (Stern's Miracle-
Gro) containing 15% total nitrogen (N), 30% available
phOSphoric acid (P205), 15% soluble potash (K20), and the
micro-nutrients Cu, Fe, Mn and Zn. The fertilizer was
applied as 15 g to 5 litres of water.

Response of the trees to varying doses of simazine
and diuron was monitored for four weeks. During this time
the degree of injury to the plants and leaves were quan-
titatively recorded at weekly intervals by visual assess-
ment (Table 4.2). In addition, measurements of height and
number of leaves were taken weekly. At the end of the ex-
periment, dry weights of leaves, stem and roots were de-
termined after drying 24 hr. at 75 C. The various measure-
ments were statistically assessed using the analysis of
variance, and a planned comparison of treatment means at

the 1% level of probability was done.

50

TABLE 4.2 CRITERIA USED FOR WHOLE PLANT AND LEAF VISUAL
SCORINGa

 

A. Whole Plant Visual Score

Dead

= Moribund

= Alive with some green tissue; no growth
= Very stunted but still making growth
Considerable (50%) growth inhibition

= Readily distinguishable growth inhibition

Some detectable adverse effect

'\1 mm {-‘W N l—‘ 0
ll

Indistinguishable from control

B. Leaf Visual Score

0 = Dead

1 = Ca. 85% leaf area dead
2 = Ca. 50% leaf area dead
3 = Ca. 10% leaf area dead
4 = Normal leaf

 

3Modified from Clay and Davison (1978).

51

RESULTS

Herbicides and rate: There were no statistically
significant differences detected in the phytotoxicity of
simazine and diuron to poplar clones in all parameters
evaluated throughout the duration of the experiment (Table
4.3). Significant differences in phytotoxicity were ob-
served, however, among the rates of each herbicide (Table
4.3). The trends in rate within each herbicide were sim-
ilar (Tables 4.4-4.7, Figure 4.1). The lower rates of
each herbicide were less phytotoxic, but at the same con-
centration diuron appeared to be less toxic than simazine.
The whole plant and leaf visual scores showed lower phyto-
toxicity at 10, 20, and 50 mg/pot of diuron compared to
the same rates of simazine (Tables 4.4 and 4.5). Total
dry weights at 10, 20 and 50 mg/pot 0f diuron were signi-
ficantly higher than the corresponding values at the same
rates of simazine (Table 4.6 and 4.7). The difference in
phytotoxicity between simazine and diuron at the same rates
began to be apparent ca. 3 weeks after the application of
the herbicides.

Clone: Highly significant treatment differences
occurred due to the clonal material used in this experiment
(Table 4.3). All parameters evaluated showed significant
clonal differences at the 1% level of probability at the

fourth week of treatment. There were also significant

52

TABLE 4.3 ANALYSIS OF VARIANCE FOR NUMBER OF LEAVES PER
PLANT, HEIGHT, DRY WEIGHT, PLANT AND LEAF SCORE
FOUR WEEKS AFTER THE APPLICATION OF VARYING RATES
OF SIMAZINE AND DIURON TO POPULUS CLONES GROWN
0N SAND CULTURE IN THE GREENHOUSE

 

’Pfobability‘LeNel of F—Statistic
Degrees Number
Source of of of leaves Dry Plant Leaf
Variation freedom per plant Height Weight Score Score

 

Herbicide 1 .97 .188 .26 .361 .335 ”'
Rate 5 .002 .0005 .0005 .0005 .0005

Herbicide x

Rate 5 .308 .095 .023 .053 .054 f
Clone 22 .0005 .0005 .0005 .0005 .0005 E
Herbicide x P
Clone 22 .0005 .0005 .0005 .0005 .0005

Rate x .

Clone 110 .083 .0005 .0005 .0005 .0005

Herbicide x
Rate x V
Clone 110 .995 .926 .023 .001 .0005

53

TABLE 4.4 WHOLE PLANT AND LEAF VISUAL SCORES PER PLANT
FOUR WEEKS AFTER APPLICATION OF VARYING RATES
OF SIMAZINE TO 21 POPULUS CLONES GROWN ON SAND
CULTURE IN THE GREENHOUSE

 

 

 

 

 

 

 

Clones Rates of Simazine
(mg/pot)

Section Tacamahaca Q 1 5 _Q 7gp 59
NE 41 11 ll 8 4 O 0
NE 388 ll 10 6 O 0 0
NC 5260 ll 11 10 9 2 O

§gction Tacamahaca

x Aigeiros

NE 218 11 ll 11 ll 8 3
Jac 7 11 ll 10 9 6 1
NE 302 11 11 8 4 3 0
NE 207 11 ll 8 6 3 0
NE 48 11 4 1 O 0 O
Jac 4 11 ll 11 9 2 0
NE 298 ll 11 10 7 0 0

Section Aigeiros
NE 17 11 11 10 6 5 0
NE 5377 ll 11 11 6 5 0
NE 5328 11 ll 11 ll 9 2
NC 5323 ll 11 ll 10 5 0
PD 222 ll 11 ll 8 7 3
NE 308 11 ll 11 10 6 1
H 47 11 11 ll 8 6 6
NE 58 11 ll 11 6 5 0
NC 5 326 11 10 9 7 4 0
NE 353 11 ll 11 10 3 0
PD 184 11 11 8 4 3 0

 

 

54

TABLE 4.5 WHOLE PLANT AND LEAF VISUAL SCORES PER PLANT
FOUR WEEKS AFTER THE APPLICATION OF VARYING
RATES OF DIURON TO 21 POPULUS CLONES GROWN
ON SAND CULTURE IN THE GREENHOUSE

 

 

 

 

 

 

 

Clones Rates of Diuron
(ms/pot)
Section Tacamahaca Q ‘1 5 ,;Q g9 59_
psi.

NC 5260 ‘ 11 11 11‘ 11 6 0 ‘
NE 388 11 ll 9 6 4 O ‘
NE 41 11 ll 10 10 8 0

Section Tacamahaca

x Aigeiros

Jac.7 11 ll 11 11 ll 4 5'
NE 302 11 ll 9 9 6 0
NE 298 ll 11 ll 8 6 5
NE 207 ll 11 11 10 8 3
Jac 4 ll 11 11 ll 4 0
NE 218 ll 11 10 4 3 3
NE 48 ’ 11 10 6 3 1 0

Section Aigeiros
NE 353 11 ll 11 11 8 5
NC 5323 ll 11 ll 11 8 6
NC 5326 11 11 ll 11 8 2
NE 17 11 ll 9 9 7 0
NC 5328 l 11 11 ll 10 5
NC 5377 11 11 ll 11 6 3
H 47 11 ll 8 8 3 0
NE 58 11 ll 11 ll 6 3
PD 184 11 ll 11 ll 8 0
PD 222 11 ll 11 ll 8 4

 

 

55

TABLE 4.6 RELATIVE TOTAL DRY WEIGHT, FOUR WEEKS AFTER THE
APPLICATION OF VARYING RATES OF SIMAZINE TO 21
POPULUS CLONES GROWN IN SAND CULTURE IN THE

 

 

 

 

 

 

 

GREENHOUSE
Clones Rates of Simazine
(mg/pot)
§gction Tacamahaca l 5 19 g9 59
.% of control.
NE 41 72 5O 25 l6 16
NE 388 68 39 18 l3 16
NC 5260 59 35 21 12 ' 7
Section Tacamahaca
xggggeiros
NE 218 81 81 49 44 33
Jac 7 100 65 44 l9 19
NE 302 100 38 20 ll 7
NE 207 85 45 35 16 15
NE 48 82 32 18 18 23
Jac 4 100 65 44 19 19
NE 298 55 27 28 23 18
_ggtion Aigeiros
NE 17 100 100 48 34 26
NC 5377 100 97 32 18 13
NC 5328 100 87 34 26 15
NC 5323 85 82 5 54 51
PD 222 100 80 48 35 31
NE 308 100 69 42 42 27
H 47 94 75 37 25 31
NE 58 100 72 38 18 14
NC 5326 100 39 38 13 10
NE 353 74 30 23 23 18

PD 184 70 45 24 17 9

 

\r—_ ‘

 

56

TABLE 4.7 RELATIVE TOTAL DRY WEIGHT, FOUR WEEKS AFTER THE
APPLICATION OF VARYING RATES OF DIURON T0 21
POPULUS CLONES GROWN IN SAND CULTURE IN THE

 

 

 

 

 

 

 

GREENHOUSE
Clones Rates of Diuron
ling/pot)
Section Tacamahaca ; 5 pp 29 5Q
. . . .% of control.

NC 5260 100 100 100 47 31
NE 388 100 82 46 12 18
NE 41 91 64 6O 27 20

Section Tacamahaca

x Aigeirog

Jac 7 100 100 100 96 96
NE 302 100 100 78 41 20
NE 298 100 100 37 25 23
NE 207 100 100 27 28 17
Jac 4 100 77 77 22 22
NE 218 94 56 38 38 36
NE 48 5O 46 36 36 23

Section Aigeiros
NE 353 100 100 100 83 83
NC 5323 100 100 100 80 58
NC 5326 100 100 100 91 21
NE 17 100 100 100 73 73
NC 5328 100 100 96 55 48
NC 5377 100 100 100 46 14
H 47 100 100 80 70 23
NE 58 100 100 100 30 27
PD 184 100 95 34 45 12

PD 222 100 94 24 34 22

57

FIGURE 4.1 RELATIVE TOTAL DRY WEIGHTS OF POPULUS
CLONES, FOUR WEEKS AFTER TREATMENT WITH
VARYING RATES OF SIMAZINE AND DIURON

58

 

  

328
c5
_:....
""""""" 53
..... E3
5- “1“ N
4_.m

 

NE48

 

llllllllllllllllllllllllllllll
O

  

 

 

 

 

 

'E ' 3
8 . 2 /"°”
“52 L 1 E (mg
as O IMAZIN -"
E In S s\\“““‘
9 5 '
LIJ
; "m“
--- ~“~
E ------- 5“ 4
04? ---- ' 4
E 3
2
3_. 1
0

.1
Figure 4

t )
PO
RON (mg/
o”J

|n

59
herbicide x clone and rate x clone interactions for tree
heights and number of leaves at the end of the experiment.
Total dry weights, whole plant and leaf visual scores
showed significant herbicide x clone, rate x clone and
herbicide x rate x clone interactions (Table 4.3). In—
jury symptoms, as measured by the whole plant and leaf
visual scores showed significant clonal differences be-
ginning from the second week after treatment at all levels
of simazine and diuron. For example, clone NE 48 exhibits
injury symptoms at l mg/pot simazine or diuron (Table 4.4
and 4.5) whereas clone NC 5328 showed only minor damage
at 20 mg/pot of simazine or diuron. At the end of the
experiment a few clones were still alive but most were com-
pletely killed at 50 mg/pot simazine or diuron (Table 4.4
and 4.5). Total dry weights at the end of the experiment
were significantly different among the clones at each her-
bicide rate (Tables 4.6 and 4.7). At the higher concen-
trations most clones were reduced in dry weights to below
50% of the controls (Tables 4.6 and 4.7). Tree heights
and number of leaves showed similar clonal differences at
the 4th week of treatment.

A few clones were observed that exhibited differ-
ential tolerance to simazine or diuron. Clone NE 353 showed
only minor injuries with diuron but was heavily reduced in
dry weights by simazine. E. deltoiges clone 222 was more

inhibited by diuron than simazine (Tables 4.6 and 4.7).

 

60

Dose-response curves: To rank the clones used in
this experiment on a relative scale convenient for com-
paring their tolerance to simazine and diuron, dose-
response curves were prepared for each clone (Figure 4.1).
The doses of simazine or diuron causing 20% (EDZO) and
50% (EDSO) growth inhibition were obtained from the dose-
response curves of each clone using total dry weights ex- r_
pressed as a percent of the control (Tables 4.8 and 4.9).
The dose response curves for different clones indicated
that the degree of response to increasing doses varied

among clone (Figure 4.1). Owing to differences in the

 

degree of response to increasing doses of simazine or
diuron, trends in ED20 and ED5O values obtained for the
clones were different (Tables 4.8 and 4.9). For example,
based on ED20 values, NC 5328 was ca eleven times more
tolerant than NE 388 to simazine (Table 4.8). However,
when this selectivity index was calculated from ED50,
(Fryer and Makepeace, 1977) clone NC 5328 was only two
times more tolerant than NE 388 to simazine. A similar
trend was observed in the tolerance of clones of diuron.
Because of the larger clonal differentials, ED20 values
were employed in ranking the tolerance of p0plar clones
to simazine or diuron.

Clonal rankings: Table 4.10 is a ranking of clone

 

in order of decreasing ED20 values. Based on this ranking,
clones NE 17, NC 5377, NC 5323, NE 218 and PD 222 were con-

sidered relatively tolerant to simazine within the range

61

TABLE 4.8 TOXICITY 0F SIMAZINE TO 21 POPULUS CLONES AS

 

 

 

 

~ a
SHOWN BY ED20 AND ED50 VALUES.
Clones ED20 ED50
§ection Tacamahaca
NE 41 1.0 4.7
NE 388 1.0 2.1
NC 5260 1.0 1.7

Section Tacamahaca

NE 218 5.2 9.5
Jac 7 2.2 8.2
NE 302 1.5 3.2
NE 207 1.2 3.8
NE 48 1.0 2.3
Jac 4 1.0 3.3
NE 298 1.0 1.2

Section Aigeiros

NE 17 6.2 9.8
NC 5377 5-9 8-6
NC 5328 5.5 7.4
NC 5323 5.2 50.0
PD 222 5.0 7.0
NE 308 4.3 8.2
H 47 3.5 7.4
NE 58 2.9 9.8
No 5326 1.3 2.8
NE 353 1.0 2.1
PH 184 1.0 6.6

I 17; 14". 'Il‘ifl

 

 

 

aDoses(mg/pot) causing 20 and 50% reduction in total dry
weights, respectively.

62

 

TABLE 4.9 TOXICITY OF DIURON TO 51 POPULUS CLONES AS
SHOWN BY ED AND ED VALUES.
20 5O
Clones EDZO ED50

 

§ection Tacamahaca

 

 

 

NC 5260 12.2 20.1
NE 388 5.0 8.6
NE 41 2.0 11.6
Sgction Tacgpahaca x
Aigeiros
Jac 7 50.0 50.0
NE 302 10.2 20.1
NE 298 6.0 7.5
NE 207 5.6 7.0
Jac 4 3.2 12.2
NE 218 1.5 6.1
NE 48 1.0 1.0
_gct;on Aigeirog
NE 353 50.0 50.0
NC 5323 22.2 50.0
NC 5326 22.2 28.5
NE 17 20.0 50.0
NC 5328 13.5 40.5
NC 5377 12.2 16.4
H 47 11.0 25.8
NE 58 11.0 14.9
NE 308 10.0 50.0
PD 184 5.8 7.8
PD 222 5.2 6.0

 

aDoses (mg/pot) causing 20 and 50% reduction in total dry

weights, respectively.

 

53

TABLE 4.10 CLONAL RANKINGS BASED ON EDZO VALUES FOR
SIMAZINE AND DIURON FOUR
TREATMENT WITH VARYING LEVELS OF THE HERBI-
CIDES.

WEEKS AFTER

 

Clonal Ranking

Clonal Ranking

 

.""- f; '1." “I... ...'1

 

 

(Simazine)a (Diuron)b
Tolerant Tolerant
NE 17 (A>° NE 5314)
NC 5377 (A) Jac 7 ”(T X A)
NC 5328 (A) NC 5323 (A)
NC 5323 (A) NC 5326 (A)
NE 218 (T x A) NE 17 (A)
PD 222 (A) NC 5328 (A)
Intermediate Intermediate
NE 308 (A) NC 5377 (A)
H 47 (A) NC 5260 (T)
NE 58 (A) H 47 (A)
Jac 7 (T x A) NE 58 (A)
NE 302 (T X A)
NE 308 (A)
Intolerant Intolerant
NE 302 (T x A) NE 298 (T x A)
NC 5326 (A) PD 184 (A)
NE 207 (T X A) NE 207 (T X A)
NE 48 (T X A) PD 222 (A)
NE 353 (A) NE 388 (T)
Jac 4 (T X A) Jac 4 (T X A)
PD 184 (A) NE 41 T
NE 41 (T) NE 218 (T x A)
NC 5260 (T) NE 48 (T X A)
NE 298 (T X A)
NE 388 (T)
aEDZO ranges for simazine tolerant clones ==>5 mg/pot;
intermediate 2 t0 5 mg/pot; Intolerant = <L2 mg/pot.
bEDZO ranges for diuron tolerant clones ==>13 mg/pot;
intermediate 10 to 13 mg/pot; Intolerant =<10 mg/
pot.

C

A = Section Aigeiros; T = Section Tacamahaca; T X A =
Tacamahaca X Aigeiros

64

of doses tested. These clones tolerated more than 5 mg/pot
of simazine before a 20% reduction in total dry weight oc-
curred. These tolerant clones belong to the section Aigeiros
except NE 218 which is an intersectional cross of Aigeiros

x Tacamahaca. Those clones considered intermediate in tol-
erance to simazine had ED20 values between 2 and 5 mg/pot.
These intermediate clones were NE 308, H 47, NE 58 and Jac- If
7, all Aigeiros clones except the inter-sectional cross I
Jae-7. Clones that had ED20 values less than 2 mg/pot were

considered intolerant to simazine. The group of intolerant

 

clones consisted of three Aigeiros clones NC 5326, NE 353

‘F
1

and PD 184; three Tacamahaca clones NE 41, NE 388 and NC
5260; and the five intersectional crosses NE 302, 207, 48
298 and Jae-4 (Table 4.10).

Clones that tolerated more than 13 mg/pot before
a 20% reduction in total dry-weight occurred were consid-
ered relatively tolerant to diuron. Tolerant clones in-
cluded NE 353, Jac 7, NC 5323, NC 5326, NE 17 and NC 5328,
again, all from section Aigeiros except Jae-7. Clones
considered intermediate in tolerance to diuron had ED20
values between 10 and 13 mg/pot. Clones in this intermed-
iate category were Aigeiros clones NC 5377. H 47, NE 58
and NE 308; Tacamahaca clone NC 5260 and Aigeiros x Tacama-
haca clone NE 302. Clones that had ED20 values less than
10 mg/pot were considered relatively intolerant to diuron
and included Tacamahaca clones NE 388 and NE 41; Aigeiros
clones PD 184 and PD 222; and Aigeiros x Tacamahaca clones

NE 298, 207, 218, 48 and Jae-4 (Table 4.10).

65
DISCUSSION

Simazine and diuron appeared to have similar phyto-
toxic effects on poplar clones used in this experiment.
The toxicity of both herbicides increased with increasing
concentration. This suggested that their mode of action
(the sequence of events that leads to death following the F.
primary response) are similar, although the mechanism of I
action (the primary biochemical or biophysical interfer-
ence impose by a herbicide that leads to lethality) may

not be the same (Moreland, 1980). Climatic factors, soil

 

textural fractions and pH affect simazine and diuron to
different degrees in the field. Simazine, an s-triazine,
is believed to be protonated in acid soil systems and
adsorbed by negatively-charged soil colloids resulting in
reduced concentrations in the solution available for plant
uptake (Weber, 1970). Diuron, a substituted urea, on the
other hand is unaffected by pH in the range of 4.3 to 7.5
(Corbin gt a;., 1971). A differential pH-dependent phyto- .
toxicity of simazine and diuron was reported (Chapter 2)
from a field soil of pH 5.4. It seemed reasonable, then,
that on a sand culture of pH 7.5 to 8.0 in a greenhouse,
simazine and diuron should express comparable phytotoxicity.
Simazine was, however, more toxic than diruon at
higher concentrations and cuased more reduction in heights
and dry weights. This difference in phytotoxicity at the

high rates was manifested in visual symptoms about the third

66
week of treatment. Simazine is less soluble than diuron
(3.5 versus 42 pme in H20 at 25 c; Mullison, 1979). This
differential solubility might have resulted in greater
leaching of diuron making it less available to the plants.
This difference in solubility is probably responsible for
about four months greater persistence of simazine than
diuron when applied at the same rate in the field (Brown, F,
1978). Diuron has also been reported to be more toxic to
fruit crops than simazine (Clay and Davison, 1978).

The Populus clones used in this study were found

 

to vary substantially in their susceptibility to simazine L
and diuron. Differences in susceptibility were visually -,
observed by the second week of treatment and by the end of
the experiment,leaf, stem and root dry weights showed sub-
stantial clonal differences in phytotoxicity. Clonal dif-
ferences in total number of leaves and height at harvest
was probably due to the lethal effect of the herbicides

at high rates rather than inhibition of leaf production

or height growth during the treatment period. Von Althen
(1979) similarly found that height growth of clones

used in his experiment was unaffected by simazine treat-
ment, while Clay and Davison (1978) found that leaf

number in strawberries showed the least response to in-

creasing doses of simazine. Rate of leaf production and

 

height growth are also believed to be more under genetic

influence and less controlled by environment or cultural

67

practices. For this reason rate of leaf production or
height growth may be less reliable for monitoring the
reSponse of tree crops to soil-acting herbicides. In
spite of the obvious drawback in the use of number of
leaves and height growth in ranking the relative tolerance
of crops to herbicides, however, Clay and Davison (1978)
found significant correlation between these parameters and P‘

other measures of herbicide effects. r

Wk.“'.a..._.f

In general, dry weights, ED20 or ED5O values or
plant and leaf visual scores are more reliable and frequent-

ly used in evaluating the tolerance of crops to soil-acting

 

I!"

herbicides (Clay and Davison, 1978; Clay, 1980; Talbert and
Fletchall, 1964; Fryer and Makepeace, 1977). Clay (1980)
observed that EDZO values gave more useful estimates of
relative tolerance in different plant species than ED50
values.

Several parameters were employed in ranking the
clones tested in this experiment, but only the ranking based
on ED20 values are shown here. Trends in all the rankings
are similar and indicated that Aigeiros poplars are rela-
tively more tolerant to simazine and diuron than Tacamahaca
poplars. Tacamahaca x Aigeiros clones appeared to be in-
termediate or intolerant to simazine and diuron. However,
at least one Aigeiros clone was found to be consistently
intolerant, while one Tacamahaca x Aigeiros clone was tol-
erant among the clones tested. However, no Tacamahaca clone

was found to be tolerant. These results are similar to the

68
field observation of von Althen, (1979) who observed that
cuttings of clones NC 5328 (I-45/5l) and NC 5323 (DN 21),
both in the section Aigeiros, were tolerant to dosages of
up to 4.5 kg/ha simazine but DJac 14, a Tacamahaca x
Aigeiros clone, was injured by a dose of 2.2 kg/ha. The
present results also confirmed the results from field
eXperiments reported in Chapter 2 that showed Aigeiros
clones NC 5323, NC 5328 and H 47 to be tolerant to doses
of up to 4 kg/ha simazine or diuron while Tacamahaca
clones NE 388 and NE 48 were injured by a dose of 2 kg/

ha simazine or diuron on various plantation sites in

 

lower Michigan.

The basis for this differential selectivity to
simazine and diuron among Populus clones is not known.
Due to its sparingly soluble nature, the major basis of
selectivity of simazine in the field, especially in plants
lacking any active metabolic pathway of degrading simazine
molecules (e.g. as in maize) is placement (Ebert and Dum-
ford, 1976). The same is true for diuron. In a sand-culture
such as used in this eXperiment all clones have equal ex-
posure to simazine or diuron within experimental limits.
Any differential tolerance, e.g., a difference in select-
ivity index of about eleven between NC 5328 and NE 388,
cannot be simply due to a physical barrier. Simazine was
reported to be actively metabolized to non herbicidal hydro-
xysimazine in Norway spruce (Picea abies) by Lind-Hoeie

(1969a), whereas Dhillon gt a;., (1968) did not observe any

69

degradation of simazine in red pine (Pings resinosa)
seedlings. Similar data for Populus is not available.

The differential tolerance to simazine and diuron
in this experiment may be due to some form of inactivation
of the herbicide molecules, e.g., by active metabolism
to hydroxysimazine (Shimabukuro, 1968) or compatmental-
ization on active binding sites (Arntzen g; a;., 1979;
Pfister gt a;., 1979). If this inactivation occurs in
Populus it is apparently under relatively strong genetic
control and could be exploited by tree geneticists in
selecting or breeding new clones insensitive to soil-

acting herbicides.

CHAPTER V

EFFECT OF SIMAZINE ON PHOTOSYNTHETIC CO2
FIXATION, CO2 COMPENSATION POINT, LEAF
CONDUCTANCE AND SPECIFIC LEAF WEIGHT OF

SIMAZINE-TOLERANT AND INTOLERANT POPULUS CLONES 1?
INTRODUCTION

The effects of triazine herbicides on photosyn-

 

thesis and water balance of agronomic crOps and weeds have ;
been studied extensively, but very few reports exist on
forest trees (Ebert and Dumford, 1976; Moreland, 1980).

In nearly all studies, the extent of transpiration re-
duction was related directly to herbicidal susceptibility
of the particular plant Species. In all cases of trans-
piration reduction by triazines, partial or complete stom-
atal closure occurred (Ebert and Dumford, 1976). Imbamba
and Moss (1971) showed that CO2 uptake is reduced more than
transpiration in the light. The inhibitory effect of tri-
azines on photosynthesis is very likely the initial cause
which leads to reduced transpiration (van Oorschot, 1976).
Besides depriving the cell of energy, inhibiting photo-
synthesis would also raise the CO2 concentration of the
cells. The effect of high concentrations of CO2 causing
stomatal closure in the light has been well documented

(Ebert and Dumford, 1979). If photosynthesis is partially

7O

71

or completely inhibited by the triazines, then, stomata
would be eXpected to remain closed or to only partially
open.

More than one reaction in the photosynthetic pro-
cess is probably affected by simazine. In addition to
inhibition of the Hill reaction, simazine (triazines) also

inhibit photosynthetic CO fixation (Moreland and Hilton,

2
1976; Moreland, 1980). Any condition that alters the pro-
cess by which CO2 is fixed or released will alter the CO2
compensation equilibrum that exists between photosyntheses
and respiration (McClelland g3 31., 1978). C02 compensa-
tion concentration, then, can be used to compare effects
of environmental conditions or chemical treatments on
photosynthesis and respiration. A highly significant
negative correlation has been demonstrated to exist be-
tween photoshythetic rate and 002 compensation point
(Heichel and Musgrave, 1969: Dickmann, 1971; Larcher, 1980).
Differences in phytotoxicity of simazine in Pogulus
clones have been reported in the field (Dickmann, g3 al.,
1978; von Althen, 1979; Chapter 2) and confirmed in green-
house studies (Chapter 4). The selectivity among POpulus
clones to simazine appears to be under genetic control.
Most of the clones tested in the Aigeiros section were rel-
atively tolerant of simazine whereas clones in the Tacama-
haca x Aigeiros intersectional hybrids were relatively in-
tolerant (Chapter 4). For example, clone NC 5328 (section

Aigeiros) tolerated up to 4.5 kg/ha simazine, whereas clone

72

NE 388 (section Tacamahaca) was injured by less than 2
kg/ha simazine in field trials (vcn Althen, 1979; Chapter
2).

A selectivity index to simazine of eleven between
NC 5328 and NE 388 was observed using a sand-culture tech-
nique in the greenhouse (Chapter 4). It was concluded
that tolerance to simazine in poplar could not be due to
positional selectivity (Chapter 4), but must depend on cer-
tain genetically-controlled physiological responses.

The objective of this study was to further char-
acterize the differential tolerance to simazine that ex-
ist among Populus clones. The effect of simazine on 002
fixation, CO2 compensation point, leaf conductance and
specific leaf weight in simazine-tolerant NC 5328 and in-

tolerant NE 388 clones of Populus were evaluated.

MATERIALS AND METHOD

Cultural: Unrooted hardwood cuttings of POpulus x
euramericana cv. fI-45/5l" (NC 5328) and P. maximowiczii
x P. trichocarpa cv. "Kingston? (NE 388) were selected for
uniformity in length, diameter and bud size. They were
raised in a greenhouse in washed sand of pH 7.5—8.0. Tem-
perature in the greenhouse was ca. 25 C during an 18 hr day
and 15 C at night. Relative humidity was between 60 and 80%.
Watering and aeration of the pots was accomplished by pour-

ing 1 litre of nutrient solution directly on the sand when

73

the surface was dry. The nutrient solution was prepared
from a 15-30—15 (N-P-K) commercial water-soluble plant
food supplemented with the micronutrients Cu, Fe, Mn and
Zn.

The plastochron index (PI) and leaf plastochron
index (LPI) concepts as deve10ped for cottonwood by Larson r-
and Isebrands (1971), were used to select the sampled
leaves. At the 4th week of growth, height, diameter and

number of leaves 20 mm or greater in length were recorded.

 

Length of the index leaf (the first leaf below the apex at
least 20 mm in length) and the leaf immediately above it
were measured for calculation of PI and LPI. At a PI of
12, the index leaf (LPI O), the 12th leaf from the base,
would be exactly 20 mm long. The next older leaf below
the index leaf has a LPI of l and so on down the plant.
Simazine treatment: As plants approached a PI of
10, pairs were selected within each clonal pool. Pairing
was based on uniformity in height, diameter and number of
leaves (PI). At a PI of 11 one plant from each pair was
randomly selected; 5 mg of simazine (80% wettable powder)
was added in 1 litre of water to the sand surface in the
pot. The other plant in the pair was left untreated. Based
on previous studies, 5 mg/pot simazine was high enough to
cause injury but not enough to kill the intolerant clone
NE 388 during the experimental period. Treated plants were

scored at each sampling time for visual injury symptoms

74

on the leaves and whole plant (see Chapter 4 for criteria
of visual assessment). Heights and number of leaves were
also recorded.

Photosynthesis, leaf conductance and C02 compen-
sation point: Measurements were made on plants 24 hr, 48

hr, 1 week and 2 weeks after treatment with simazine (Table

 

r
5.1). The measurements corresponded with PI's of 11, 13, F
18 and 25 for NE 388, and 11, 12, 16 and 21 for NC 5328.
For both clones determinations were made on leaves of LPI
4 and 9 at 24 hr, 4 and 10 at 48 hr, and 5 and 11 at 1 week E

after treatment. Two weeks after treatment determinations
were made on leaves of LPI 5, 12 and 21 for NE 388 and LPI
5, 11 and 18 for NC 5328. The purpose of this scheme was
to monitor physiological activity within the developing,
newly mature and older leaf zones. The sampling scheme
consisted of both a vertical series and a horizontal or
aging series (Table 5.1). The vertical series allows com-
parison of leaves in similar states of develOpment while
the horizontal series allows comparisons of the same leaf
position with time (Dickmann, 1971).

Photosynthetic measurements were made in the green-
house where the plants were grown. Prior to determinations,
conductance of the abaxial leaf surface was measured with
a Li Cor LI-65 Autoporometer equipped with a horizontal
Kanemasu-type sensor (Kanemasu gt gl., 1969). Leaf temper-

ature was measured with the bead thermister built into the

.xmapmpmm so an ooonHom who come one; mazesmuzmmoe HmOHonchzza scan; :0 mm>mmqt

 

 

 

 

 

 

 

 

o mm
H :N
m mm
m Nm
s o Hm
*n H ON
8 N AH
A m o as
o s H As
0 *m N 0 0H
0H m m H ma
HH m 3 N 3H
*NH w *m m H MH
ma A o s a o NH
as ed A sm m a o 0 Ha
mH *HH m 0 m N H H OH
8H NH A A s n m m o
AH ma oz m *m s m m m
mH :H *HH 0 o *m *3 t: a
no AH ma NH oz A o m m o
om be ma Add m A c o m
#HN NH 3H NH 0 m m m 3
mm sod ma ma oH A m w m
MN 0H 0H 3H *HH *0H #m to N
so om AH ms «H as OH OH H
. . . . . . . . . . . . . . . . . . . . . .qu. . . . . . . . . . . . . . . .
Ammmm
Amm Hay Adm Hay Aos HAV Asa Hmo and HAV Ame HAV Add Hmv Add Hmv soszv
mmnmz mmmm oz own mz mmmm oz mom mz mmmm oz mom oz ommm oz .oz omen
mxmoz N xooz H .m: m: .h: :N
mmcHumEHm poflNflwavszz acmspmohe youm< plomm
.mzHNasz oe mmzomomz mom
mmzue moon<> ea omzzmsmz mz<qmom ozoo» zoo AHAV xmozH zozzooamanm
oz< mmmzoz o<~zmm z<mq oe onzsqmz zH AHmav xmozH zozzooem<go maze H.m mamas

76

porometer by appressing it to the lower leaf surface.
Photosynthetically active photon flux density (PAPFD)
was determined with a Li<3or LI-85 light meter equipped
with a quantum sensor. Measurement of PAPFD was made

parallel to the leaf surface, assuring i situ radiation

 

conditions by maintaining continuity of canOpy architec-
ture (Kriedemann 23 gl., 1964). Air containing 332 ppm

002 (5.0 uCi 1 ‘1 1“

COZ) was passed over both surfaces
of a leaf by clamping the treatment chambers of a pulse
labeling devise (HcWilliam gt a1., 1973) over the leaf
for 20 seconds. Flow rate was 80 ml min-l, sufficient
to minimize the boundary layer resistance and prevent
depletion of CO2 in the chambers. The exposed area (0.5
cm2)immediately cut from the leaf with a 1 cm cork borer
and placed into a scintillation vial containing 1.5 m1
NCS tissue solubilizer (Amersham Corp.)

Scintillation vials containing leaf discs and NCS
were placed in an oven for 24 hr at 50C. Samples were al-
lowed to cool for 30 min and then bleached by the addition
of 0.5 ml H202. Twenty-four hours later, 17 m1 of a
scintillation fluid containing 1000 ml tolune, 400 ml
methyl cellosolve and 60 ml Spectrafluor (Amersham Corp)
was added. After an additional 24 hr. dark equilibration
period, samples were counted in an Isocap 300 liquid
scintillation system (Nuclear Chicago) at room temperature.

Rate of photosynthesis, eXpressed as weight of CO2 taken

up by the leaf per unit time and leaf area, was calculated

 

77

using a formula similar to that of McWilliam gt gt.
(1973).

Leaves used for photosynthetic measurements were
excised and CO2 compensation points determined using a
Mylar-bag technique (Dickmann and Gjerstad, 1973). The
area of each individual leaf then measured with a Li Cor
LI-3000 leaf area meter.

Leaves were dried in an oven at 75-C for 48 hr.
and weighed for calculation of specific leaf weight (SLW),
an index of the relative density of a leaf and a sensitive
measure of environmental influences (Ledig, 1974). SLW
was determined to monitor morphological changes occurring
in leaves following simazine treatment.

The experimental design was a split-split-plot
factorial. Two replications of each paired measurement
were made, representing eight trees and 16 leaves per
measurement time. Means were compared at the 0.05% level

of probability by Duncan's New Multiple Range Test.

RESULTS

The condition of leaves and plants, heights and num-
ber of leaves two weeks after treatment with 5 mg/pot
simazine is shown in Table 5.2. There were no injury symp-
toms visible in both NC 5328 and NE 388 from the time of
treatment through the first week. In the second week after
treatment clone NE 388 began to show significant injury

symptoms, whereas NC 5328 did not (Table 5.2). The

78

TABLE 5.2 PHYSICAL CONDITION OF POPULUS CLONES NE 388
AND NC 5328 TWO WEEKS AFTER TREATMENT WITH

 

 

 

 

5 MC/POT SIMAZINE.

Clone Treatment Leaf Plantb Hei ht Number
t§core Score (cm ofiteavgg

NE 388 Control 4 7 62 25

Simazine 2 5 58 25 E
NC 5328 Control 4 7 53 21

Simazine 4 7 55 22 3
aLeaf score: 0 = dead leaf; 4 = normal leaf.

b

Plant score: 0

dead plant;

7 = normal plant.

79

injury symptoms in NE 388, which consisted of acute
chlorosis and "burning" of leaves, was confined to the
zone between LPI 11 and 18 (PI 25). This chlorotic re-
gion correSponded to the zone of recently mature leaves
and consisted of about one-third of the entire leaf area
of the plant.

The leaf conductance of NE 5328 in this experi-
ment ranged between 0.08 and/0.13 cm 3'1 (Table 5.3).
There were no significant differences detected between
treated and control plants nor among the different leaf
positions within each treated plant for both NC 5328 and
NE 388 throughout the duration of the eXperiment.

There were no significant differences detected in
CO2 compensation points between treated and control plants
or among the different positions within treated plants of
NC 5328 at 24 hr, 48 hr, 1 week and 2 weeks after treat-
ment with 5 mg/pot simazine (Table 5.4). Compensation
points of NE 388 plants treated with simazine, however,
showed significant increases over control plants at 48
hr, 1 week and 2 weeks after treatment. There was also
more variability in compensation points within NE 388
plants than within NC 5328 plants. Leaves in the recently
mature zone, where symptoms of simazine injury were most
apparent, showed higher compensation points than leaves
in the zones below and above.

Significant differences were found between NC 5328

and NE 388 in the rate of C02 fixation. No significant

 

80

TABLE 5.3 ABAXIAL LEAF CONDUCTANCE OF POPULUS CLONES NE
388 AND NC 5328 AFTER TREATMENT WITH 5 MG/POT
SIMAZINE.

 

Period After Treatment3

 

 

 

Clone Treatment Leafb 24 hr 48 hr 1 week 2 weeks
Position _____ ‘_____
, cm s-l. . . . . . .
NE 388 Control E .12 .08 .09 .11
RM 09 .12 .13 09
OM --- --- --- .09
Simazine E 12 .10 ll .11
RM 11 .11 ll .10
OM --- --- --- .09
NC 5328 Control E .10 .11 .09 .10
RM .10 .11 .11 .10
0M --- -—- --- .12
Simazine E .11 .10 .10 .11
RM .1O .10 .11 .10
0M --- --- --- .lO

 

aNo means within columns differ significantly at the 5% level.

bE = expanding leaves; RM = recently mature leaves;
OM = older mature leaves.

81

TABLE 5.4 CO2 COMPENSATION CONCENTRATIONS OF POPULUS
CLONES NE 388 AND NC 5328 AFTER TREATMENT
WITH 5 MG/POT SIMAZINE.

 

Clone Treatment

 

 

NE 388 Control

Simazine

NC 5328 Control

Simazine

Leaf
Posi

OM

RM
OM

RM
OM

['11

24 hr. 48’hr. 1 week 2 weeks
____ti_02_______________
. .ppm.

69 be 74 7O 55
65 abc 71 58 47
-- -_ -- 49
6? abc 87 123 80
66 abc 71 182 115
-- -- -- 55
66 abc 69 59 47
64 abc 61 56 4O
-- -- -- 40
70 c 68 61 44
65 ab 61 57 44
-- -- -- 40

Period After Treatment a

 

b

 

aMeans within columns followed by the same letter do not
differ significantly at the 5% level.

bE= expanding leaves; RM = recently mature leaves; OM =
older mature leaves.

 

82

differences in rate of photosynthesis were detected be-
tween treated and control plants of NC 5328, although
treated plants showed slightly higher rates of CO2 fixa-
tion at 24 hrs, 48 hrs, and 2 weeks after treatment. The
rate of 002 fixation was significantly reduced in simazine
treated NE 388 plants 1 week and 2 weeks after treatment
(Table 5.5). There were also significant differences in
the degree of inhibition among different leaf positions
on NE 388 plants; eXpanding leaves were less inhibited
than recently mature leaves at 1 week and 2 weeks after
treatment. Older mature leaves at 2 weeks after treat-
ment did not Show any inhibition at all (Table 5.5).

A significant difference in the response of NE 388
and NC 5328 to simazine treatment was also reflected in
Specific leaf weights (Table 5.6). Clone NC 5328 was again
not affected but a significant reduction in specific leaf
weight occurred 1 week and 2 weeks after treatment of clone

NE 388. All leaf positions sampled were uniformly reduced.

DISCUSSION

Differences in photosynthetic response to simazine
treatment have been demonstrated in Pogulus clones NC 5328
and NE 388. Additions of simazine at 5 mg/pot had no de-
leterious morphological or physiological effects on NC 5328
but reduced the rate of CO2 fixation, increased CO2 compen-
sation concentrations and lowered the specific leaf weight

of NE 388. These deleterious physiological effects of

-3 £511,155, .

 

83

TABLE 5.5 LEAF PHOTOSYNTHETIC RATE OF POPULUS CLONES
NE 388 AND NC 5328 AFTER TREATMENT WITH 5

MG/POT SIMAZINE

 

Clone Treatment

 

 

NE 388 Control

Simazine

NC 5328 Control

Simazine

Leafb

Team

{'11

RM
OM

RM
OM

Period Atter Treatmenta

 

 

 

24 hr 48 hr 1 week 2 weeks
.mg 002 dm‘2 hr ‘1.
1.7 a 11.6ab 5.9 b 8.2 b
5.8 ab 14.6b 5.3 b 10.6 had
-- -- -- 9.7 bc
4.3 a 8.7a 2.3 a 3.3 a
10.0 bc ll.3ab 1.7 a 2.8 a
-- -- -- 8.6 b
11.0 c 11.5ab 5.5 b 13.3 Cd
9.4 bc 10.7ab 5.3 b 11.0 bcd
-- -— -- 7.9 b
12.1 c 14.5b 5.4 b 13.9 d
9.0 bc 12.1ab 5.0 b 12.9 Cd
-- -- -- 7.3 b

 

aMeans within columns followed by the same letters do not
differ significantly at the 5% level.

bE = expanding leaves; RM = recently mature leaves; 0M =
older mature leaves.

84

TABLE 5.6 SPECIFIC LEAF WEIGHT 0F POPULUS CLONES NE 388
AND NC 5328 AFTER TREATMENT WITH 5 MC/POT

 

 

 

 

 

SIMAZINE
Pertggggfter Treatmenta
Clone Treatment Leafb 24 hr 48 hr 1 week 2 weeks
Position _____. _____
mg cm-z. . .
NE 388 Control E 3.0 a 4.1 a 4.3 b 4.0 b
RM 3 7 a 4 2 a 4.4 b 4 l b
0M -- -- —- 4 4 b
Simazine E 3.8 a 4.3 a 2.6 a 2.4 a
RM 3.5 a 4.5 a 3.0 a 2.7 a
0M -- -- -- 2 7 a
NC 5328 Control E 4.0 a 4.2 a 4.4 b 4.0 b
RM 3.7 a 4.5 a 4.1 b 4.6 b
0M -- -- -- 4.4 b
Simazine E 4.0 a 4.4 a 4.5 b 4.3 b
RM 4.0 a 4.0 a 4.2 b 4.3 b
0M -- -- -- 4.4 b

 

aMeans within columns followed by the same letters do not
differ significantly at the 5% level.

bE= eXpanding leaves; RM = recently mature leaves; 0M =
older mature leaves.

85
simazine on NE 388 were detected 48 hr. after eXposure of
plants to simazine and generally became more pronounced
thereafter. Visual symptoms of injury did not become
evident until two weeks after treatment, however. The
length of this period before onset of visual injury symps
toms was similar to that reported for simazine and diuron
on intolerant clones of Pogulus in Chapter 4.

The differential effect of simazine on CO2 fixation
in two clones of Populus reported here is similar to ob-
servations of Radosevich and Appleby (1973) that photo-
synthesis was completely inhibited by simazine in suscep-
tible biotypes of common groundsel, whereas resistant bio-
types were unaffected. Similar differential effects of
triazine herbicides on photosynthesis in different bio-
types of plant species have also been reported by Souza
Machado gt g;.(l977) and Radosevich gt gt. (1979). The
effect of triazines on CO2 compensation concentration in
susceptible and tolerant biotypes has received less atten-
tion. In one report bentazone application to entire
morning glory increased 002 compensation by ca. 300% over
untreated control plants 4 days after application (McLeL-
land gt g;., 1978). The increased CO2 compensation points
observed after the intolerant NE 388 was treated with .
simazine in this eXperiment correlates with the reduced
rates of CO2 fixation also shown by this clone.

The basis for this differential response of NE 388

and NC 5328 might be due to differences in translocation,

86

accumulation, active metabolism, or binding of the simazine
compound in different plant parts. These factors have been
reported as responsible for differential tolerance between
susceptible and resistant biotypes of some crops and weeds
(Werner and Putnam, 1980; Radosevich gt g_l_._., 1979). The
basis for observed differential response of NE 388 and NC

5328 to simazine is being investigated further.

mm .1 c -‘U'l. I,

Leaf stomatal conductance appeared not to be af-
fected by simazine in both tolerant and intolerant clones :

of Populus within the experimental period. Stomatal con-

 

ductance, a reciprocal of stomatal diffusion resistance, L
is directly proportional to the stomatal pore width (Larcher,
1980). Thus, by showing no effect on conductance, simazine
probably did not directly affect the rate of gas flow through
the stomata in this eXperiment. It is now generally agreed
that the effect of photosynthetic inhibitors like the tri-
azines on transpiration is secondary (van Oorshot, 1974,
1976; Ebert and Dumford, 1976). Sharkey (1980), for ex-
ample was able to inhibit photosynthesis for a period of

4 days without any apparent effect on stomatal pore size

in excised leaves of Xanthium strumarium using DCMU (diuron)
or atrazine. The results reported here further confirm that
within a short period (2 weeks in this eXperiment) photo-
synthesis could be reduced substantially without affecting
stomatal conductance. However, the necrosis induced by
herbicides would ultimately lead to decreased transpiration

rate and conductance. The onset of this necrotic processes

87
is indicated in clone NE 388 by the reductions in SLW
that occurred after 1 week.

The response to simazine toxicity in the tolerant
clone NE 388 varied depending on the position of the crown
sampled. Inhibition of photosynthesis and increased CO2
compensation points were more pronounced in the region of
recently mature leaves, but was also apparent in the re-
gion of eXpanding leaves. The differential response be-
tween leaf positions may be due to the degree of vascular-
ization and its causal effects on xylem translocation. For
example, Larson and Isebrands (1971) observed that inter-
nodes in the recently mature zone (LPI 9, 10, 11 or 12 in
this eXperiment) have complete secondary vascular tissues
with well developed secondary vessels and rays. They also
observed that the eXpanding leaf zone (LPI 4 or 5 in this
exPeriment) consisted of immature primary vascular tissues.
Field observations at periods of drought stress in Populus
plantations correlates well with the described trend in
vascularization of the crown.

For example, wilting is first observed in the apex
and uppermost leaves while drought-induced leaf scenescence
occurs first in the lower-most leaves (Dickmann, 1980),
indicating that the resistance to water movement into leaves
is highest in these regions. Because simazine is trans-
ported in the xylem, the crown region into which water most

freely moves would be expected to accumulate greater levels

88
of simazine. It is also known that the lower leaves of
Potulus plants are declining in physiological activity
(Dickmann, 1971; Dickmann and Gordon, 1975), reducing

their sensitivity to simazine.

CHAPTER VI

SUMMARY AND CONCLUSIONS

Fast-growing forest trees like the P0pulus are
prime candidates for intensive production of wood. How-
ever, growth can be substantially limited if competition
for water, space and nutrient is not eliminated or re-
duced by controlling competiting vegetation. Chemicals,
when applied properly, offer the most effective and cheap
method of weed control. Only a few chemicals among which
are simazine and diuron, have potential for use in p0plar
plantations. But at rates effective for adequate weed
control injury to some Populus clones often occurs. The
studies reported here examined the differential effect of
simazine (2—chloro-4, 6-bis (ethylamino) — s - triazine),
and diuron (3-(3,4 -dichlor0phenyl) - l, l-dimethyl urea)
on survival, growth and physiology of selected hybrid
Pogulus clones.

In field studies, clonal differences in establish-
ment, growth and biomass yield of simazine and diuron
treated Populus was demonstrated. Clones NC 5323 and H
47 performed well at the Tree Research Center (TRC); NC
5323 and NE 41 were the best at Dansville and Manistee.

The response of the clones to simazine and diuron follow

99

90

similar pattern. High doses of each herbicide were toxic
to all clones except H 47, which appeared to be relatively_
tolerant. Simazine at 2 kg/ha was found adequate for
acceptable weed control, survival and biomass yield at

TRC and Dansville. However, at Manistee simazine was in-
effective due to the low pH of the surface soil but diuron
at 2 kg/ha was suitable.

A single initial tillage operation at the beginning
of the season benefitted all clones tested at all herbi-
cide rates on all sites. Survival growth and yield were
higher on tilled plots when supplemented with herbicides
compared to either tillage or herbicide alone. This was
probably due to the increased persistence of the herbi-
cides on the tilled sites. However, the enhancement of
tree establishment due to increased moisture and soil con-
tact was probably also significant.

The effect of simazine in causing an increase in
total foliar nitrogen of Populus clones beyond that due to
elimination of competiting vegetation was demonstrated.

The stimulatory effect of simazine on total foliar nitro-
gen was dependent on the clone, rate of simazine and length
of time after application. Clone H 47 and NC 5323 treated
with 2 to 3 kg/ha simazine gained nearly 12% in total foliar
nitrogen over the untreated weed-free control at the middle
of the season, the period of most active growth. There was
also a corresponding increase in height growth. Nitrogen

content of clone NE 388 and NE 48 were unaffected but height

91
growth of NE 388 was significantly inhibited by sima-

zine.

In greenhouse studies, Populus clones from sec-
tions Tacamahaca and Aigeiros were assayed for tolerance
to five levels of simazine and diuron. Selected clones
included both intra and intersectional hybrids as well as
pure P. deltoides. Washed sand of pH 7.5-8.0 was used to
eliminate or reduce the influence of edaphic factors on
herbicidal behavior. Although no morphological basis for
selectivity was observed, each of the clones could be clas-
sified as either tolerant, intermediate or intolerant to
simazine or diuron in the range of concentrations tested.
Tacamahaca hybrids and intersection crosses between Tacama-
haca and Aigeiros were relatively intolerant to both her-
bicides, whereas Aigeiros clones were relatively tolerant.
Examples of intolerant clones include P. maximowiczii x P.
trichocarpa (NE 388) and at maximowiczii x 2. cv. "berolinen-
sis" (NE 48). The 3. x euramericana clones fCanada blanc"
(NC 5323) and "1 45/51" (NC 5328) were among the most tol—
erant tested. A selectivity index of eleven between NC 5328
and NE 388 was observed with simazine.

Based on the field and greenhouse studies, it is
evident that clonal differences in the response of Populus
clones to simazine could not be due to positional select-
ivity, but must depend on certain genetically-controlled
physiological responses. Differential photosynthetic re-

sponses to simazine were observed in Populus clones NC 5328

92
and NE 388. Additions of 5 mg/pot Simazine had no deleter-
ious morphological or physiological effects on NC 5328 but
reduced the rate of C02 fixation, increased CO2 compensa—
tion points and lowered Specific leaf weight of NE 388.
The deleterious effects of simazine on NE 388 were de-

tected 48 hr. after exposure of plants to Simazine and

generally became more pronounced thereafter. Visual symp- E
toms of injury in intolerant clone NE 388 lagged ca. 12 7
days behind the onset of inhibitory effects on physio- r
logical processes and changes in specific leaf weights. _

p

 

The response to simazine toxicity in the intoler-
ant clone NE 388 was different depending on the position
of the crown that was sampled. Inhibition of photosyn-
thesis and increased CO2 compensation points were more
pronounced in the region of recently mature leaves, followed
by the region of expanding leaves. The lower crown region
with older mature leaves showed no visual symptoms of in—
jury; rate of photosynthesis and CO2 compensation concen-
trations were not affected. The differential response due
to leaf position was probably due to morphological patterns
of vascularization and their causal effect on translocation
of herbicide into the different regions. Since simazine
transport is apoplastic, the degree of development of the
xylem system in each crown region will differentially af-

fect its distribution and subsequent toxicity.

93

The differential clonal responses to simazine and
diuron demonstrated in the field and greenhouse studies
could be due to a number of factors, such as differential
uptake and translocation, metabolism of simazine to non-
toxic hydroxysimazine or chloroplast binding character-
istics among Potulus clones. A study to evaluate differ-
ential simazine uptake, translocation or metabolism in
intolerant and tolerant clones is already underway. Further
studies will be necessary to examine differential herbicide-
binding to the chloroplast as a possible major factor in
differential simazine or diuron tolerance among Populus
clones. Stuides to confirm heritability of the mechanism
of tolerance among the Populus clones is essential to know
if such mechanism could be transferred to clones with other
desirable characteristics but susceptible to herbicide
toxicity.

Breeding for herbicide tolerance among Populus
may be further down the road: immediate selection of her-
bicide tolerant Populus clones based on the parentages

can now be achieved with a high degree of safety.

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