826
NOTES
-,
AND E. P. 0DU-M. 1955. Trophic structure and productivity
of a windward
coral
reef community
on Eniwetok
Atoll.
Ecol.
Monogr. 25 : 291-320.
POMEROY, L. R.
1959.
Algal productivity
in
Limnol. Oceanogr.
salt marshes of Georgia.
4: 386-397.
RILEY, G. A. 1956. Oceanography
of Long Island Sound, 1952-1954.
9. Bull. Bingham
Oceanogr. Collect. 15 : 324-344.
SMALLEY, A. E.
1959.
The growth
cycle of
Spartina and its relation to the insect populations in the marsh, p. 96-100.
In Proc.
Conf. Salt Marshes, Univ. Ga.
STEEMANN NIELSEN, E. 1952. The use of radioactive carbon ( C4) for measuring organic
production
in the sea. J. Cons., Cons. Penn.
Int. Explor. Mer 18: 117-140.
1959.
Energy
flow in the salt
TEAL, J. M.
marsh ecosystem,
p. 101-107.
In Proc.
Conf. Salt Marshes, Univ. Ga.
PHOTOSYNTHESISAND RESPIRATION IN MYRIOPHYLLUM
AS RELATED TO SALINITY'
ABSTRACT
After about 20 hr at low light intensity in
the laboratory,
photosynthesis
was depressed
in MyriophyUum
spicatum tips at a salinity
of 32%,, but respiration
was not affected.
Neither
photosynthesis
nor respiration
was
depressed at salinities of 16% and less. When
on lO-14hr
the plants
were maintained
light-dark
cycles at moderate
light intensities, after 48 hr and up to 10 days, photosynthesis was depressed at salinities of 16%
below that of plants in Albemarle Sound water, although respiration
remained high. The
depression of photosynthesis
at high salinity
and its effect on the P: R ratio are assumed
to play a part in controlling
natural distribution of M. spicatum in estuaries.
Field observations in the Chesapeake
Bay area indicate that the distribution
of
Myriophyllum
spicatum L. ( Eurasian watermilfoil)
and many other macrophytes
can be affected by salinity
(Anderson
1964; J, H. Steenis, personal communication ) . The species is stunted or killed
when the salinity is over 13-14%0. In addition to the effect of normal salinity gradients on the growth and distribution
of
M. spicatum in estuaries, drastic salinity
changes associated with seawater intrusion
can result in eradication of the plant.
The mechanisms by which supraoptimal
salinities affect the distribution
of higher
plants occurring mainly in freshwater are
(1967)
not known, but as Sculthorpe
l Supported
in part by a National
Foundation
College Science Improvement
to East Carolina University.
Science
Grant
SPICATUM
L.
pointed out, they are probably varied and
complex. We report here experiments designed to show the effects of increasing
salinities on photosynthesis
and respiration and, therefore, on the P : R ratio in
M. spicatum.
MATERIALS
AND METHODS
Vegetative, floating fragments of M. spicatum about 15-20 cm long were collected
in June along the southern shore of Albemarle Sound, North Carolina, near the
mouth of the Alligator River where the
weed has recently become established.
These were maintained for 3 weeks in
sound water in an aquarium growth chamber. The salinity of the water was l%o.
Illumination
was provided by diffuse fluorescent light supplemented with incandescent light giving around 2 mW/cm2 at the
water surface as measured with a radiometer. Light periods of 8 hr alternated with
16-hr dark periods. The daily variation in
temperature of the water was 1621C with
the warmer temperatures
during
light
periods.
About 20 hr before each run, tips 2 cm
long were removed and placed singly in
test tubes in a series of artificial seawater
( Seven Seas) solutions ( group I) or in a
series of Albemarle Sound water-artificial
salt solutions ( group II). The sound water was filtered and kept refrigerated until
used. Salinities in each group were at 0,
4, 8, 16, and 32%~. The 32%0 solution of
group II was prepared by adding salts
827
NOTES
I
-
0
1ooL0
I
4
6
12
I
16
20
24
28
7
32
Salmrty
FIG. 1. Group I. ReIationships between salinity (c/00) and net photosynthesis
(0, evolution)
and respiration
(0, uptake) in tips of Myriaphyllum spicatum in artificial
seawater.
Each point
represents
the mean of three replicate
experiments; vertical bars represent the range.
directly to sound water, providing a condition not found in nature. These test tubes
were maintained in a water bath at 25 -C 0.2
C with a light intensity from “cool white”
fluorescent bulbs of about 2 mW/cm2.
Respiratory
(dark) and net photosynthetic rates were determined in fresh solutions by polarographic
measurements of
oxygen changes with a Clark oxygen electrode (Yellow
Springs Instr. Co.) and
Servoriter II recorder (Texas Instr. Inc.).
Measurements in 10 cc of solution in a
vial at 25 +- 0.5C were continued until a
steady rate was obtained (usually S-10
min). A preliminary experiment indicated
that photosynthesis occurs satisfactorily at
25C without the formation of gas bubbles
often associated with higher temperatures.
The maximum light intensity of 30 mW/
cm2 within the vial was provided with
2,300-W incandescent lamps. The light
was passed through 6 cm of cooled water.
Continuous magnetic stirring resulted in
continuous rotation of the tip during all
measurements.
Runs were in triplicate,
and changes in oxygen concentrations were
,
4
8
16
I
24
32
Salmty
FIG. 2. Croup II. Relationships
between increased salinities of sound water with proportionate salt solutions
(except
at 32S0 where salts
were added directly)
and net photosynthesis
( O2
evolution)
and respiration
(02 uptake) in tips of
Myriophyllum
spicatum.
Each point represents
the mean of three replicate experiments;
vertical
bars represent the range.
calculated on the basis of oven-dry weights
of the tips (frum 5-15 mg).
In another experiment on the effects of
salinity on P : R ratios, 4 tips were maintained for 10 days in 1,000 cc of each of
4 different solutions: sound water; deionized water; 50% seawater ( 16X0) -50%
sound water (OS?L); seawater 16%~. The
light-dark cycle was lo-14 hr with a light
intensity of 5 mW/cm” from fluorescent
and incandescent sources. Respiratory and
photosynthetic rates were measured every
second day. Other procedures were as
described above.
RESULTS AND DISCUSSION
Responses were rather variable (Figs. 1
and 2), as were those found for this plant
by Spence and Chrystal ( 1970), who determined photosynthetic rates by the Warburg technique, and Stanley ( 1970), who
studied photosynthesis and respiration using both Warburg and infrared CO8 analytical methods. However, it is apparent
that exposure of tips to salts at 32%0alone
or mixed in sound water drastically lowers
828
NOTES
o-4
Salt
Salts
solutions
or solutions
+ sound water
TABLE 1. Net photosynthesis
(pg Or min-’ g-’
evolved),
respiration
(pg 02 min-’ g-l uptake),
und P: R ~attis of Myriophyllum
spicatum tips
after 10 days in vari0u.s solutions
Net photosynthesis
Salin-
ity
(%I
Solution
Sound water
Deionized
FIG. 3. Photosynthesis-respiration
(P : R) ratios
of Myriophyllum
spicatum tips in salt solutions
and salt solution mixed proportionally
with Albemarle Sound water except at 32% where salts
were added directly to sound water.
the net photosynthetic
rate (as measured
by O2 evolution) although the respiratory
rate (as measured by O2 uptake) is little
affected. The decrease in photosynthesis
at the highest salinity is more obvious
when the P : R rate at each salinity is
plotted (Fig. 3). Lower salinities (group
I, 4 and 8X0) seem to enhance the P : R
ratios over both no salinity and natural
salinity controls, but this effect is not as
strong as the depression of the ratios at
32%0 and shows no consistent pattern.
Further evidence of the effects of salinity on P : R ratios was obtained in the
second experiment (Table 1). The process
primarily
contributing
to depressed P : R
ratios in salt solutions was again decreased
photosynthesis, with respiratory rates staying within a comparatively narrow range.
This effect appeared after 2 days in all
treatments except Albemarle Sound water.
In addition, the respiratory rate for tips
in the sound water was consistently lower
than for the rest throughout the lo-day
period.
Measurements
of photosynthesis
and
respiration in intact aquatic macrophytes
based on oxygen changes may not give a
true picture, since such plants tend to
accumulate oxygen in the stems which is
then recycled (Wetzel 1965; Hartman and
Brown 1967). Oxygen accumulation
in
water
Respiration
P: R
1.0
106”
34*
4.1t
0
61
42
2.5
50% seawater
50% sound water
16.5
65
42
2.6
Seawater
16.0
54
44
2.2
* All values are the mean for 4 tips in each solution,
t P : R values significant
beyond the 0.01 level with
analysis of variance with arcsin conversion.
our experiments was probably negligible,
as there were few air spaces in the immature tissues of the short tips used.
Our rates compare favorably with those
of Stanley ( 1970)) who used apical fragments of M. spicatum about 10 cm long
in a nutrient solution. For example, in a
time-rate experiment
on photosynthesis,
he measured CO2 uptake with infrared gas
analysis and obtained a range of 6944.5
pug CO2 min-l g-l dry wt at 25C with high
light intensities.
Other results with this
plant (Steemann Nielsen 1947; Spence and
Chrystal 1970) are given as percent of
maximum photosynthesis and are therefore
not directly comparable.
Our work leaves many unanswered
questions. We have established that in the
laboratory differential
responses to salinity in photosynthesis and respiration do
occur in M. spicatum. Significant reductions in the photosynthetic rate can occur
at a salinity ( 16%~) approximating
those
( U-14%0) deleterious to the plant under
estuarine conditions. A study of the relation of purely osmotic effects to the effects
of specific ions both in the intact plant
and with chloroplast preparations may be
enlightening.
CHERYL
GRAHAM
Department of Biology,
East Carolina University,
Greenville, North Carolina
F. MCGAHEE
J. DAVIS
27834.
829
NOTES
REFERENCES
ANDERSON, R. R.
1964.
Ecology
and mineral
nutrition
of Myriophyllum
spicatum L. M.S.
thesis, Univ. Maryland,
College Park. 50 p.
HARTMAN, R. T., AND D. L. BROWN. 1967.
Changes
in internal
atmosphere
of submerged vascular hydrophytes
in relation
to
photosynthesis.
Ecology 48: 252-258.
SCULTHORPE, C. D. 1967. The biology
of
aquatic vascular plants.
E. Arnold.
610 p.
SPENCE, D. H. N., AND J. CHRYSTAL. 1970.
Photosynthesis
and zonation
in freshwater
macrophytes
1. New Phytol. 69: 205-215.
STANLEY, R. A. 1970. Studies on nutrition, pho-
A COMPACT POTENTIOMETRIC
IN SITU DETERMINATION
ABSTRACT
A rugged, compact probe (2 cm overall
diameter, 9 cm overall length)
is described
that enables pH, pS2-, and Eh to be measured in situ. A miniature
glass electrode is
mounted in an epoxy resin body to which
the metal electrodes are cemented. The glass
electrode is mercury filled and has a cylindrical sensing membrane.
The resulting probe
is relatively
insensitive
to vibration
and to
changes in light intensity and the glass electrode equilibrates
rapidly
to ambient temperature and pressure changes. Construction
details are given.
With appropriate
holders
the probe can be used for measurements
in
the water column, in the sediment, or in the
intertidal
zone. The performance
of the unit
is illustrated
by data from a stagnant basin
model and from an estuarine survey.
The recent work of Ben-Yaakov and
Kaplan (1968, 1969) has shown that in situ
pH measurements are useful for studying
the properties of lake and ocean waters
and for investigating the relationships between the sediment and the water column.
Other studies suggest that the sulfide activity is a significant
parameter in the
development of sedimentary sulfide minerals (Berner 1963) and in the distribution
of bottom fauna (Fenchel and Riedl 1970;
Theede et al. 1969). In addition, a correlation between the sulfide activity and the
Eh (the potential generated at a bright
platinum electrode immersed in the sam-
tosynthesis, and respiration
in Myriophyllum
spicutum L. Ph.D. thesis, Duke University,
Durham, N.C. 129 p.
STEEMANN NIELSEN, E. 1947. Photosynthesis
of aquatic plants with special reference
to
Dan. Bot. Ark. 12:
the carbon-sources.
1-71.
WETZEL, R. G. 1965. Techniques and problems
of primary
productivity
measurements
in
higher
aquatic
plants
and periphyton,
p,
249-267.
In C. R. Goldman [ea.], Primary
productivity
in aquatic environments.
Mem.
1st. Ital. Idrobiot.
18 (suppl. ), also Univ.
Calif. Press. 1966.
SENSOR
OF
pH,
NOVEL DESIGN.
pS”-, AND Eh
OF
ple, and usually expressed on the standard
hydrogen scale) of a stagnant sediment
has been demonstrated in sediments from
widely separated regions (Berner 1963;
Skopintsev et al. 1967; Whitfield
1969).
In other work Eh and pH have been considered as parameters for characterizing
sediment and water types (Baas Becking
et al. 1960; Krumbein and Garrels 1952).
So that these correlations may be explored
in detail a probe is required that will enable geologists and biologists to measure
all three parameters in the course of
routine sampling. This approach is particularly
important
in onshore waters,
estuaries, and lakes where small-scale patterns are significant
and where detailed
surveys are feasible. A probe designed for
this purpose should be compact, rugged,
and easy to operate. In particular the glass
electrode used for pH measurement must
be robust and reliable.
Since all three
parameters (pH, pS2-, and Eh) are sensitive to changes in environmental
conditions they are best measured in situ rather
than by sampling techniques.
Most earlier probes for in situ work have
been designed specifically to measure pH
and have been rather complex in construction (e.g., Disteche 1964; Ben-Yaakov and
Kaplan 1968). Probes designed to measure
have
several parameters simultaneously
usually been bulky assemblages of com-