Download Depth distribution of photosynthetic activity in a Myriophyllum

LIMNOLOGY
May 1974
AND
OCEANOGRAPHY
1
Volume
19
Number
3
Depth distribution of photosynthetic activity in a
Myriophyllum spicatum community in Lake Wingral
Michael S. Adams and John Titus
Department
of Botany,
University
of Wisconsin,
Madison
53706
Michael McCracken
Department
of Biology,
Texas Christian
University,
Fort Worth
76109
Abstract
Photosynthetic
rates and productivity
of Myriophyllum
spicatum L. were examined in the
littoral by incubating
shoot sections at three rooting depths using a 14C technique.
At a
rooting depth of 240 cm, the interrelation
of biomass and photosynthetic
rates resulted in
the production
of 56% of the total photosynthetic
productivity
within 100 cm of the water
surface in May. In August, 57% of the total productivity
occurred within only 20 cm of the
surface. Variations in the depth distribution
of biomass, due to differing growth and sloughing patterns, resulted in different
depth relations of photosynthesis
at the other rooting
depths. Light extinction and light adaptation
of photosynthetic
tissues were other factors
determining
the depth relations of photosynthesis.
Myriophyllum
spicatum L., the Eurasian
watermilfoil, is a submergent aquatic macrophyte introduced into the United States in
the 19th century, which has achieved nuisance levels of growth in lakes and slowmoving waterways of several states (Smith
et al. 1967; Anderson 1972). We have studied its production dynamics in the littoral of
Lake Wingra (Madison, Wisconsin), a shallow eutrophic lake with a surface area of
140 ha (Poff and Threinen 1962) and a
bottom mainly composed of marl, with sand
and organic matter in places (Nichols and
Mori 1971). The University of Wisconsin
Arboretum borders the lake on its southern
shore, and the northern shore is dominated
1 Contribution
No. 124 of the Eastern Deciduous
Forest Biome, US-IBP, funded by the National
Science Foundation
under Interagency
Agreement
AG 199, 40-193-69 with the Atomic Energy Commission-oak
Ridge National Laboratory.
LIMNOLOGY
AND
OCEANOGRAPHY
by recreational and residential areas. The
littoral occupies about 43 ha, or 31% of the
surface of the lake, most of it colonized by
M. spicatum.
Early in spring, Myriophyllum
plants
grow from established
rootstocks and
mainly short shoots more or less straight up
to the surface, then grow along the surface
to form a canopy in areas of dense growth.
Meanwhile leaves are sloughed from the
lower stems. Thus, by mid- and late summer most of the active photosynthetic tissues ( leaves) are located within the canopy
near the water surface, whereas leafless
stems predominate below the canopy. This
growth form corresponds to the modified
herb type (Ikusima 1965).
The primary objectives of the work summarized here were to obtain measurements
of the natural depth profiles of photosynthetic production and to examine factors in-
377
MAY
1974,
V.
19(3)
378
Adams et al.
fluencing differences in photosynthetic rates
exhibited by those profiles. Photosynthetic
profiles of plants incubated at depths of
natural occurrence have been examined for
both phytoplankton
( Ryther 1956; Talling
1966) and macrophytes
(Ikusima
1965,
1966). All studies show pronounced differences in photosynthetic
rates with depth
and raise questions concerning the factors
of greatest importance in controlling these
differences.
Historically,
light has probably received more attention than any other
single factor. Early workers on aquatic
macrophytes (Ruttner 1926; Schemer 1934;
Meyer et al. 1943) incubated plant samples
of similar weight, age, and preconditioning
regimes at different depths; resulting profiles of photosynthetic rates were considered
to be a mcasurc of light extinction.
Maximum photosynthetic rates for macrophytes
were reported at water depths from O-5 m,
apparently dependent on turbidity, incident
light intensity, and the species under investigation. Stanley ( 1970) has examined the effccts of temperature on photosynthesis and
respiration of Myriophyllum
spicatum. Current flow (Westlake 1967), calcium carbonate encrustations (Wetzel 1960), and water
chemistry ( Unni 1972) are additional potentially important factors that may vary
with depth in macrophyte communities, but
WC did not investigate these.
One biological
factor that obviously
changes with depth is biomass distribution.
This may not directly affect the rate of photosynthesis, but has a bearing on total photosynthctic productivity within a given stratum. Sorokin (see Koblenz-Mishke
1960)
devised a system to investigate this factor
with incubations of diff crent phytoplankton
populations at different depths. We used a
similar design in our experiments with macrophytes.
Qualitative
changes in biomass with
depth may also be important. For macrophytes such as M. spicatum, tissue age and
leaf/stem biomass vary with depth. Light
adaptation occurs in both algal (Jorgensen
( Gessner 1938;
1969) and macrophytic
Spence and Chrystal 1970; Ikusima 1966)
species. We have considered changes in
light, temperature, and quantity and quality
of biomass with depth. The remaining factors we either controlled or regarded as less
important.
We thank W. H. Stone for his technical
assistance in the field and laboratory and R.
R. Kowal for his help in the statistical analyses.
Methods
During the summers of 1971 and 1972,
we followed canopy and stem distribution
of carbon uptake in the Myriophyllum
community of Lake Wingra by a l”C technique
modified
slightly
from that of Wetzel
( 1964). WC incubated sections of Myriophy2Zum in 510-ml glass bottles of lake water, to which 5 @i ‘“C-NaHCOn
were
added, clamped to aluminum poles within
the macrophyte community.
We have not
tested the effects of sectioning Myriophyllum on carbon uptake rates, but sectioning
EZoden canadensis had no significant effect
on its photosynthetic rates (Ikusima 1965).
We always collcctcd lake water from just
below the surface, to avoid surface films
and to ensure uniform chemical regimes
for all sections in each experiment. To minimize nutrient and carbon depletion problems, incubation periods were limited to
2 hr, after which we first washed plant sections to remove periphyton and then quickfroze them in liquid nitrogen for transfer
to the laboratory. We have not determined
the exact significance of 14C uptake for M.
spicatum, but assume it provides a measure
of photosynthetic activity more closely approximating net than gross photosynthesis.
Throughout this paper, we refer to I‘% uptake as carbon uptake, or simply photosynthesis, No dark bottles were incubated in
the course of these experiments. In previous
14C experiments (Adams and Titus uapublished), the highest dark carbon fixation
rates were always < 5% of the lowest carbon uptake rates observed in the light.
In all field experiments, we measured irradiance with a recording
pyranometer
(13elfort) and temperature with a thermis( YSI ) . Water samples
tor-thermometer
were routinely collected for each experi-
Myriophyllum
photosynthesis
with
ment, and pH was measured with a portable
meter (Sargent-Welch)
equipped with a
combination electrode.
WC report three types of experiments :
The construction of the natural profile of
photosynthetic
production
with depthThree shoots from a common rootstock
were collected, cut into lo-cm sections with
attached leaves, placed in bottles to which
carbon-14 was added, and incubated at their
natural depths. The bottles contained differing quantities of plant material (0.14-1.44
g dry wt) to simulate the natural depth distribution
of biomass-- and its accompanying
- light environment. ‘l’hesc experiments were
completed at three rooting depths (SO, 150,
and 240 cm) at approximately 3-week intervals in the 1972 growing season. The
sampling sites were chosen at the intersection of randomly selected parallel transects
with the desired depth contours in the west
end of the lake.
Incubation of terminal sections at several
depths within the water column--We
designed these experiments to vary light and
temperature conditions while holding other
factors relatively
constant, At a rooting
depth of 180 cm, growing tips were sampled
from O-IO-cm depth of water and incubated,
three per bottle, at 15-cm intervals down to
180 cm. To minimize the effects of tissue
variability,
this experiment was replicated
with three tips incubated and analyzed together; all bottles contained about the same
plant weight (0.2-0.35 g) and had similar
self-shading characteristics. A previous experiment (Titus and Adams unpublished)
with six replicates of three tips each incubated under the same conditions yielded a
coefficient of variability among carbon uptake rates of 14.5%. Ruttner (1926) and
Golubic ( 1963) performed similar cxperiments on M. spicatum but not within natural communities.
Incubation at the same depth of plant
sections collected from different
natural
depths-Our
intention here was to test the
effects of light adaptation, leaf surface/biomass, and tissue aging on photosynthetic
activity. Three Myriophyllum
shoots rooted
in 150 cm of water were collected, cut into
379
depth
/
NICHROME
WIRE
O2 OR N2
._f’4C-C02
Fig. 1. The chamber used for
plant samples containing
14C. After
bustion in pure oxygen, the chamber
with nitrogen.
TRAP
oxidation
of
sample comair is purged
LO-cm stem sections with attached leaves,
and incubated at the surface at the collection site. The experiment was repeated with
bottles incubated 75 cm below the surface.
Dry weights for the plant samples varied
from 0.09 to 0.39 g.
Plant samples were returned to the laboratory, lyophilized,
and exposed to concentrated HCl fumes for 10 min to remove
any l”C-monocarbonates
precipitated
on
leaf surfaces during the experiments (Wetzel 1965), dried overnight at 95°C and
weighed. For selected experiments, leaves
and stems were weighed separately, then
combined for further analysis. The dried
Adams et al.
380
5
25.0
z
33
s
$
0
E
F
24.0
23.0
22.0 I21.0 I20.0 I-
-
)-
-
-
I-
Percent of total plant photosynthesis
Percent of total plant weight
Temperature
at incu bation depth
~-...-..,a
-
1
)-
)-
-
-
-
I
1
IO
70
00
100
90
110
Distance from growing tip (cm)
50
70
60
00
90
100
110
120
130
150
140
160
170
I60
I90
200
220
210
230
240
Water depth (cm)
30.0
-..jy
-... o--o
-...
-a-
. .._..,
q - . ..-...-
q - ,,__...
0 -...-...
-...
-o-.
-
.,,_..,
!O.O
-0
10.0
__---
o”-
//-
o-----o-----o-----
t
d--o
L0
4
0.0-
‘;
2
0.6-p
B
O------o
o----...-o
i
-5
L‘
0
m
0.4.
Percent of total plant photosynthesis
Percent of total plant weight
Temperature
at incubation
depth
B
0
CT 0.2E
60
0
00
100
120
Distance
0
20
40
60
00
I40
from
100
Water
I , t , I , I ,
I60
180
200
220
growing
120
depth
I40
(cm)
I
240
tip (cm)
160
I80
200
220
240
+
c
al
0
L
2
Myriophyllum
photosynthesis
samples were ground to powder, and IO-mg
subsamples were wrapped in ashless filter
paper and burned in oxygen in a chamber
developed here ( Fig. 1). Evolved CO2 and
14C-C02 was trapped in 5 ml of ethanolamine, A 0.2-ml aliquot of the ethanolaminc
was then pipetted into a modified Bray’s
solution (Bray 1960) and counted in a
scintillation counter (Packard Tri-Carb) .
Water samples were titrated to determine
total alkalinity (Am. Public Health Assoc.
1965), from which total carbon was calculated using the table of conversion factors
in Saunders et al. ( 1962). This enabled calculation of carbon uptake rates according
to their formula, which includes an isotope
correction factor of 1.06.
Linear regression and correlation ( Steel
and Torrie 1960) was used for analysis of
several treatments and for comparisons between treatments. For some statistical comparisons we had to express data as percent
of maximum photosynthesis because rates
were expressed in different units.
Because assumptions of linearity and independence were not always appropriate,
the Kendall rank correlation test (Wilcoxon
and Wilcox 1964) was also used for the nonparametric comparison of trends observed
in the data.
Unpaired t-tests (Steel and Torrie 1960)
were also used for group comparisons.
Results and discussion
Photosynthesis
profiles
Two natural profiles of photosynthesis
with depth for the 240-cm water depth class
are shown in Fig. 2, representing stages in
the growth form of Myriophyllum.
Figure
2A shows the photosynthetic profile on 26
May 1972, when the tips of plants rooted in
240 cm of water were 50 cm from the surface. Photosynthetic
rates, temperature,
percent of total plant photosynthesis, and
percent of total plant weight are all shown
for each of the lo-cm depth classes. Aver-
with
381
depth
age surface total irradiance for the period
of incubation was 1.15 langleys min-‘. Temperature changed about 4°C with depth
through the water column occupied by the
plants. The photosynthetic rate of the top
depth class in which plants are found is
slightly greater than in the third and fourth
depth classes; the overall pattern seems to
bc a plateau in the uppermost 4 or 5 depth
classes and a gradual decline in photosynthetic rates with increasing depth. Greatest
biomass concentration in the depth class
80-90 cm below the water surface coupled
with high photosynthetic
rates made that
class the most productive. Of the total photosynthetic productivity,
56% occurred in
the top 100 cm of the water column.
Figure 2B shows the profile on 14 August 1972, also for shoots rooted at 240 cm.
Photosynthetic rates, temperature, percent
total plant weight, and percent photosynthesis are shown for all depth classes. At this
time, maximum canopy formation, which
occurred in July for the 240-cm depth class,
was reduced by some sloughing of tips.
However, terminal sections were still growing along the surface. The mean surface irradiance was 0.92 ly min-l. Temperature
decreased quite rapidly to about 50 cm,
then only slightly down to the bottom.
Again there was an apparent plateau of photosynthetic rates near the surface, followed
by a much more rapid reduction than earlier in the year. This effect is magnified by
the depth distribution of biomass, resulting
in the contribution of 57% of the total photosynthetic production by plants within only
20 cm of the surface. Biomass changes follow a pattern similar to that of temperature,
except for the increases in the two lowest
depth classes. Even in this shallow littoral,
dense subsurface concentrations of macrophytes, by hindering circulation, may have
induced stratification
of tempcraturc and
possibly of other factors. WC usually found
maximum photosynthetic
rates in the top
10 cm, although occasionally pcnk photo-
Fig. 2. Carbon uptake of lo-cm shoot sections of Myriophyllum spicatum incubated
depths. Rooting depth of shoots was 240 cm. A. 26 May 1972; B. 14 August 1972.
at
natural
382
Adams et al.
100 -
60 A ------A
A-A
0 ------O
60-
()-3Ocm
30 - 60cm
60-80cm
40 -
ct7
CL
20-
I
/
I
I
I“0-------------
n
O-30cm
30-60cm
60-90cm
90-120cm
120-150cm
150 -180cm
210-240cm
expressed as percent of total photosynthesis
of photosynthesis,
Fig. 3. Seasonal depth distribution
(PS) within 30-cm depth classes. A. Water depth = 80 cm; 13. water depth = 240 cm. Values less than
2% are not shown.
synthesis occurred down to 50
surface (Fig. 213 and data not
approximate
correspondence
photosynthetic depth profiles
cm below the
shown). The
of these to
for both Pot-
amogeton crispus and Vallisneria asiatica
(Ikusima 1965), the latter with a growth
form different from that of M. spicatum, indicates caution in assigning “typical” pho-
Myriophyllum
photosynthesis
with
383
depth
6.0
-
-
-
-
-
0
IO
20
30
40
50
60
70
80
Distance
50
60
70
80
90
100
110
120
130
90
100
from
140
Water
110
growing
150
depth
160
130
140
150
160
170
160
190
190
200
210
220
230
240
tip (cm)
I70
180
(cm)
Fig. 4. Net photosynthesis
of lo-cm
sections of Myriophyllum
depths, expressed on a leaf weight basis. Data of 26 May 1972.
tosynthetic depth profiles to macrophyte
species.
A comparison of maximum photosynthetic rates in May and August (Fig. 2),
both at high light intensities, indicates pronounced seasonal variation. Figure 3 shows
seasonal patterns in the depth distribution
of photosynthetic production, regardless of
such rate diffcrcnces.
The percentage of
total photosynthesis was calculated for all
depth classes, each representing the consolidation of three lo-cm classes. For plants
rooted at a water depth of 80 cm, seasonal
trends based on four field experiments are
clear ( Fig. 3A). Near the beginning of the
growing season, in early May, the shoot
apices lie at 30 cm and, accordingly, tissues
in the lower 50 cm of the water column
(represented by the lower two depth classes)
contribute all the photosynthetic
activity,
The top depth class rapidly increased in importance on succeeding dates, almost to the
exclusion of contributions by the lower two.
120
spicatum
incubated
at natural
The results for rooting depths of 240 cm
( Fig. 3B) are in many ways similar to those
at 80 cm. All depth classes below 60 cm are
unimportant early in the season. Plant parts
in the second depth class first increase in
percentage of photosynthesis
as lower
depths become shaded out, then decrease
in July as the top class attains nearly 90%
of the total photosynthesis.
Late summer
sloughing of plant parts, particularly
tips,
and the concomitant partial opening of the
canopy, may explain the depth distribution
on the last date, which is the same as that
in Fig. 213. The percentage of photosynthesis in the top depth class has noticeably dcclincd by 14 August, whereas the second
depth class has increased. The sprouting
of new growing tips from rootstocks and
lower stems is evidenced in the slight increase contributed by the lowest depth class
( Fig. 2B and 3B ) . This late season sprouting may produce the shoots which we have
observed to persist beneath winter ice cover
384
Adam
Table 1. Statistics of linear regression and correlation
on nonrelativixed
and relativixed
data.
Treatments:
A-surface
incubation,
photosynthetic rates expressed on a total weight basis; Bsurface incubation, leaf weight basis; C--75cm
incubation, total weight basis; D--75cm
incubation,
leaf weight
basis; E-natural
depth incubation,
total weight basis; F-natural
depth incubation,
leaf weight basis.
et al.
Table 2. Summary
of statistical
comparisons
of treatments
by linear regression and Kendall’s
rank correlation test. Treatments described in Table 1.
Treatments
compared
Linear
regression
Form of data
A
C
A
B
E
and
and
and
and
and
B
D
C
D
F
Relativized
Relativized
Raw
Raw
Relativized
Kendall
Results
Assoc.
*
t
*
*
?
+
z
z
2
Id
p:
C
-.0057
-.a5
D
+.0030
+.60
E
-.0061
-.98
F
-a0032
-.84
and to develop rapidly after ice-out in
spring. The same phenomenon may account for the slight increase in percent contribution of the bottom depth class at a
rooting depth of 80 cm (Fig. 3A), but the
production of new tips at that rooting depth
was not as striking as at 150 and 240 cm.
In addition, sloughing of plant parts was
not as evident in the 80 as in the 240-cm
class.
The results of experiments at the 150-cm
class are less readily interpreted and are
not shown here. They indicate two important sloughing periods, rather than the one
shown for 240 cm in Fig. 313. Patten (1954)
and Nichols ( 1971) documented two postflowering
sloughing periods for M. spi-
T
NS
+
i
+
*No overlap
of 95% confidence
intervals
slopes.
tNo overlap
of 99% confidence
intervals.
fsignificant
(0.05 level)
association
shapes.
§Highly
significant
(0.01 level).
E
Signif.
of
of
curve
catum; we observed two such periods for
the 1970 growing season in Lake Wingra,
but they were less distinct in 1971 and 1972.
A combination of the depth relations of
photosynthesis reported here with diurnal
variations in photosynthesis
of growing
tips and seasonal variations in tip photosynthesis have yielded a calculation of total
community productivity
(Adams and McCracken unpublished).
We should caution
that the depth relations which we report are
based largely on experiments performed in
late morning to midafternoon:
a 24-hr cycle, with changing angles of incoming radiation, doubtless would change the depth relations. Considering the properties of low
angle irradiance and light penetration into
lakes, in both early morning and evening the
upper depth classes would probably contribute an even greater proportion of the
total photosynthesis.
Factors controlling the
photosynthetic profiles
We recalculated the data of 26 May (Fig.
2A) on a leaf weight rather than a total
weight basis, to eliminate variation due to
changes in quantities of photosynthetic tissue with depth. This transformation
reduccd the differences among the carbon
uptake rates (Fig. 4). After the data of
Figs. 2A and 4 had been expressed in relative terms, linear regression and correlation
( treatments E and F: Table 1) indicated
Myriophyllum
photosynthesis
with
-
0
90
105
17
I
60
75
385
depth
120
135
n
m
-
150
165
I60
_-
fncubation depth (cm)
Fig. 5. Net photosynthesis
phyllum spicatum community.
(Ps)
of growing
tips incubated
high negative correlation coefficients, of
-0.98 and -0.84, for the relations C uptake :
unit shoot dry wt and C uptake : unit leaf
dry wt. The 99% confidence intervals of
the slopes of the two relations do not overlap (Table 2). Kendall’s rank correlation
test (Table 2)) however, indicated that the
shapes of the two figures show highly significant positive correlation.
Thus the expression of carbon uptake rates on a leaf
weight basis showed that changes in quantities of photosynthetic
tissue with depth
accounted for a significant amount of the
variation observed in Fig. 2A, but did not
alter the general decreasing trend in the
relation of carbon uptake versus depth,
Most of the remaining variation was probably due to differing light intensities and
light adaptation, as temperature changes
during this experiment were not great.
The effects of light adaptation would be
at different
depths
within
the Myrio-
expected to counter rather than to accentuate those of light attenuation.
Figure 5
shows results representative of the experiments designed to examine the effects of
light alone, in which growing tips collected
at a rooting depth of 180 cm were incubated
at different
depths. Again, temperature
changes with depth were slight. Mean surface light intensity during the course of the
experiment was 0.50 ly min-l. The effects
of light are dramatic with a nearly exponential decline in tip photosynthetic rates with
depth. In comparable studies with growing
tips of a number of macrophyte species,
Manning et al. ( 1938) and Meyer and Heritage ( 1941) also found decreasing photosynthetic rates with depth. However, others
found maximum photosynthetic
rates at 1
to 5 m below the surface (Ruttner 1926;
Schemer 1934) ; Ruttner’s ( 1926) study included M. spicatum.
et al.
6.0
El
5.0
40
-
30
-i
2
5
20
IO
0
- a,
1
-
:I
m
0
0
20
40
60
80
r-n
JO-
r
2.0.
1.0.
0
-
20
40
DISTANCE
60
80
-r
100
120
FROM GROWING TIP (cm)
Fig. 6. Net photosynthesis
of lo-cm sections of Myriophyllum
spicatzcm from different
depths incubated at two common depths. A-Incubation
at the surface, expressed on a total weight basis; B-incubation at the surface, cxpresscd on a leaf weight basis; C-incubation
at 75 cm, expressed on a total
weight basis; D-incubation
at 75 cm, expressed on a leaf weight basis.
A natural concomitant of the effect of
light on photosynthesis is its effect on macrophyte establishment
and growth, discussed by Peltier and Welch (1969, 1970)
and Spencc and Chrystal ( 1970).
Incubation of sections from different natural depths at a common depth provided
uniform physical and chemical conditions
during incubations. Attention is focused on
the effects of light adaptation, and again on
quantities of photosynthetic
tissue, in the
experiments summarized in Fig. 6. Figure
6A shows photosynthetic
rates of MyriophyZZum sections from different
natural
depths incubated at the surface; mean irradiance level was 0.46 ly min-l. Photosynthesis decreased with distance from the
growing tips, which approximately corresponded to the natural depth of the section
before incubation.
Transformation
of the
same data to a leaf weight basis nearly climinated the variation ( Fig. 6B), though the
three highest photosynthetic rates are still
found in the top half of the plant. Linear
regression on relativized data for each figure ( Tables 1 and 2) revealed that the 95%
confidence intervals of the slopes do not
overlap. Kendall’s rank correlation test indicated that the general trends of the two
curves are significantly
positively
associatcd. Thus, again, the transformation
of
photosynthetic rates to a leaf area basis removed most, but not all, of the variation.
The photosynthetic activity of plant sections incubated at 75 cm, approximately
half the plant length and half the water
depth, is presented similarly (Figs. 6C and
I3 ) . Irradiance was 0.06 ly min-l at 75 cm
during the experiment. The nearly linear
(r = -0.85) decline of photosynthesis with
Myriophyllum
photosynthesis
with
387
depth
Table 3. Matrix of statistics of F-tests (upper
increasing distance from the tip in Fig. 6C
right) to compare within group variances and unis similar to that in Fig. 6A, but differences
paired t-tests (lower left) to compare group means.
in magnitudes of photosynthetic
rates are Bl-Surface
incubation,
first 7 sections from the
quite pronounced. We suggest that these growing tip; B2-surface
incubation, second 7 sections: Dl-75cm
incubation.
first 7 sections: 02
differences are due to differing light levels.
’
incubation, second ? sections.
Expressing the 75-cm incubation results on --7&m
a leaf weight basis reverses the downward
trend, and photosynthetic rates actually increase with increasing distance from the tip
(Fig. SD). We conclude that short-term tissue aging has little effect on photosynthetic
potential in this case. Linear regression on
relativized data indicated no overlap of the
99% confidence intervals of the slopes of the
data in Figs. 6C and D. Kendall’s rank correlation test indicated a nonsignificant but
ncgativc association between the trends of
the two curves. Variability remaining after
* Significant
at 0.05 level.
conversion to a leaf weight basis (Fig. 61)
t Significant
at 0.01 level.
and particularly in 6D) we attribute to the
effects of light adaptation. To clarify these
results, we used further statistical tests. test indicated a significant difference bePlant sections for each incubation depth
tween the within-group
variances.
were arbitrarily
divided into two groups :
The comparison between Bl and Dl
one in which sections naturally occurred in yielded a highly significant difference bethe upper half and another for sections in tween group means. This is interpreted to
the lower half of the plant length. The mean that the upper leaves utilize relatively
means and within-group
variances of sev- high light intensities more efficiently than
eral combinations of four groups of obser- low light intensities. Thus, differences in
vations were compared (Table 3). Com- photosynthetic response of upper and lower
parison of the means of the photosynthetic
lcavcs are apparently substantiated. By dirates of groups Bl and Dl (see Table 3) rect laboratory methods, Gessner ( 1938),
with those of groups B2 and D2, rcspec- Ikusima ( 1966)) and Spencc and Chrystal
tivcly, revealed no significant differences
(1970) also found evidence of light adapin within-group
variances or means, al- tation in a variety of aquatic macrophytes.
though plant parts farther from the growing
Whether light adaptation in MyriophyZZum
corresponds to one of Jorgcnscn’s (1969)
tip ( Fig. 6D) seemed better able to utilize
the low light levels at 75 cm. Thcrc is also two types of light adaptation in algae is not
no significant difference between means of known.
B2 and D2; indicating that the tissues from
Conclusions
greater natural depths did not respond sigVariations of MyriophyZZum photosynthenificantly differently to the two light levels.
sis
with depth are very pronounced even in
It should be emphasized that even the surthe
relatively shallow littoral of Lake Winface irradiance was low on this particular
gra. These depth relations arc variable for
day, however. The possibility of photoindifferent water depths within the macrohibition of photosynthesis in lower leaves phytc community, possibly because of difby much higher light intensities has not fcrences in hormonal control of flowering
been ruled out. The lack of a significant
and mortality.
Temporal
variations
in
difference between means of 132 and D2 depth relations of photosynthesis are quite
must be accepted with caution, as the F- apparent from the seasonal study, and diurL.
rl
Adams et al.
388
E. I. CLAY. 1943. Effect of depth of imnal change should also be considered in the
mersion on apparent photosynthesis
in subdevelopment of models of primary producEcology 24: 393merged vascular aquatics
tivity.
399.
The factors apparently most important
AND A. C. HE~UTAGE. 1941 Effect of
tuibidity
and depth of immersion on apparent
in causing variations in M. spicatum photophotosynthesis
in Ceratophyllum
demersum.
synthesis with depth are light and depth
Ecology 22: 17-22.
distribution
of photosynthetic
tissue, in NICHOLS, S. A. 1971. The distribution and conagreement with Sorokin’s experimental aptrol of macrophyte
biomass in Lake Wingra.
proach
( Koblenz-Mishke
1960).
Light
Univ. Wis. Water Rcsour. Center Rep., OWRR
B-019-Wis.
111 p.
adaptation is also a factor for Myriophyllum.
p,
AND
S.
Mom.
1971. The littoral macroTissue aging with depth does not seem of
phyte vegetation
of Lake Wingra.
Trans.
prime importance.
Temperature,
current
Wis. Acad. Sci. 59: 107-119.
flow, and chemical factors may take on in- PATTEN, B. C. 1954. The status of some American species of Myriophyllum
as revealed by
creased importance when the Myrioph yZZum
the discovery of intergrade materials between
community structure is such as to hinder
M. exalbescens Fern. and M. spicatum L. in
circulation and induce stratification.
New Jersey.
Rhodora 56: 213-225.
References
AMERICAN PUBLIC HEALTH ASSOCIATION. 1965.
Standard methods for the examination
of watcr and wastewater,
12th cd.
ANDERSON, R. R. 1972. Submerged
vascular
plants of the Chesapeake Bay and tributaries.
Chesapeake Sci. 13 ( suppl. ) : S87-S89.
BRAY, G. A. 1960. A simple efficient
liquid
scintillator
for counting aqueous solution in
a liquid scintillation
counter.
Anal. Biochem.
1: 279-285.
GESSNER, F. 1938. Die
Beziehung
zwischen
Lichtintensitat
und Assimilation bei submersen
Jahrb. Wiss. Bot. 86: 491Wasserpflanzen.
526.
GOLUBIC, S, 1963. Hydrostatischer
Druck, Licht,
Int.
und submerse Vegetation im Vrana-See.
Rev. Gesamten Hydrobiol.
48: l-7.
IKUSIMA, I. 1965. Ecological studies on the productivity
of aquatic
plant communities
1.
Measurement
of photosynthetic
activity.
Bot.
Mag. Tokyo 78: 202-211.
1966. Ecological studies on the produc-.
tivity of aquatic plant communities
2. Seasonal changes in standing crop and productivity of a natural submerged community
of
Vallisneria
denseserrulata.
Bot. Mag. Tokyo
79: 7-19.
JORGENSEN, E. G. 1969. The adaptation
of
plankton algae. 4. Light adaptation in diffcrent algal species. Physiol. Plant. 22: 13Q71315.
KOBLENZ-MISHKE, 0. J. 1960. On the study of
primary production
in the sea by Soviet sciInt. Rev. Gesamten IIydrobiol.
45:
entists.
319-326.
1938.
MANNING, W. M., C. JUDAY, AND M. WOLF.
Photosynthesis
of aquatic plants at different
depths in Trout
Lake, Wisconsin.
Trans.
Wis. Acad. Sci. 31: 377-410.
MEYER, B. S., F. H. BELL, L. C. TIIOMPSON, AND
PELTIER, W. I-I., AND E. 38. WELCEI. 1969. Factors affecting
growth of rooted aquatics in a
river.
Weed Sci. 17: 412-416.
-,
AND -.
1970. Factors
affecting
growth
of rooted aquatics
in a reservoir.
Weed Sci. 18: 7-9.
POFF, R. J., AND C. W. TH~INEN.
1962. SurWis.
face water resources of Dane County.
Conscrv. Dep., Madison.
RUTTNER, F. 1926. Uber die Kohlensaureassimilation cinigcr Wasserpflanzen
in vcrschicdenen
Tiefen des Lunzer Untersees.
Int. Rev. Gesamten Hydrobiol.
Hydrogr.
15 : l-30.
RYTEIER, J. H. 1956. Photosynthesis in the ocean
Limnol.
as a function
of light
intensity.
Oceanogr. 1: 61-70.
SAUNDERS, G. W., F. B. TRAMA, AND R. W. BACEIMANN.
1962. Evaluation
of a modified
Cl’
technique for shipboard estimation of photoMich. Univ. Great
synthesis in large lakes.
Lakes Rcs. Div. Publ. 8. 61 p,
SCIIOMER, H. A. 1934. Photosynthesis
of water
plants at various depths in the lakes of northeastern Wisconsin.
Ecology 15: 217-218.
SMITEI, E. E., T. F. HALL, JR., AND R. A. STANLEY.
1967. Eurasian watermilfoil
in the Tennessee
Valley.
Weeds 15: 95-98.
1970. PhoSPENCE, D. H. N., AND J. CIIRYSTAL.
tosynthesis and zonation of freshwater macrophytes. 2. Adaptability
of species of deep and
shallow water.
New Phytol. 69: 217-227.
STANLEY, R. A. 1970. Studies on nutrition, photosynthesis, and respiration
in Myriophyllum
spicatum L. Ph.D. thesis, Duke Univ., Durham, N.C. 128 p.
STEEL, R. G. D., AND J. H. Tonnm.
1960. PrinMcGrawciples and procedures of statistics.
Hill.
behavior in
TALLING, J. F. 1966. Photosynthetic
stratified
and unstratified
lake populations
of
J. Ecol. 54: 99-127.
a planktonic diatom.
study of the
UNNI, K. S. 1972. An ecological
macrophytic
vegetation of Doodhadhari
Lake,
Myriophyllum
photosynthesis
Raipur, M.P. 3. Chemical factors.
Hydrobiologia 40: 25-36.
WESTLAKE, D. F. 1967. Some effects of lowvelocity currents on the metabolism of aquatic
macrophytes.
J. Exp. Bot. 18:
187-205.
WETZEL, R. G. 1960. Marl encrustation
on hydrophytes
in several Michigan
lakes.
Oikos
11: 223-236.
-I
1964. A comparative
study of the primary productivity
of higher aquatic plants,
periphyton,
and phytoplankton
in a large,
with
depth
389
shallow lake.
Int. Rev. Gesamten Hydrobiol.
49: 1-61.
1965. Necessity for decontamination
of
-a
filters in CL4 measured rates of photosynthesis
in fresh waters.
Ecology 46: 540-542.
WILCOXON, F., AND R. A. WILCOX.
1964. Some
rapid
statistical
approximate
procedures.
Ledcrle Labs., Pearl River, N.Y. 60 p.
Submitted:
2 May 1973
Accepted: 17 December 1973