Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
mesophylls (Pearcy & Ustin, 1984). As salt
concentrations increase, the uptake of water by the
plant is inhibited, thus greatly affecting processes
involving respiration and photosynthesis. In some
terrestrial species, transpiration is affected by increased
salinity as the stomata’s water vapor conductance is
decreased (Biber, 2006). The leaves of several
organisms have even shown signs of damage with the
slightest changes in salinity (Flowers et al., 1985).
Based on these similar previous studies, it is perceived
that increased salt concentrations interfere with the
plant’s primary biological processes.
The objective of this research was to observe
the effects that salinity has on the photosynthetic rates
of S. virginica. The hypothesis tested was whether the
plant would have a maximum photosynthetic rate in a
freshwater solution, and if a high salinity level would
damage the plant. Photosynthetic rates were
determined by measuring the rate of oxygen
production. The plants were introduced to three
different salinity levels: 0%, 3.5%, and 6.0%. All test
groups were studied under the same ambient
conditions. By subjecting the plants to two different
saline solutions, we were able to experiment with the
plant’s natural seawater environment and also one in
which the salt level was significantly higher.
Materials and Methods
S. virginica were obtained from the marshes in
Newport, California. The plants were cut at the stems,
leaving the lateral branches intact. Each plant was
weighed out to 10 g to ensure uniform mass for all
samples.
Each of the saline solutions was prepared in a
beaker using ordinary table salt (NaCl) and distilled
water. The concentrations prepared were 0%, 3.5%,
and 6.0%. Prior to the experiment, the plants were
immersed in their respective solutions and left to
acclimate for a period of thirty minutes. One hundred
watt lamps provided a light source for the plants. The
lamps were placed forty inches away from the beakers.
To measure the photosynthetic rates, data
loggers equipped with oxygen meters (Pasco TM PS-
2002) were used. After the plants had been given time
to adjust to their environments, the oxygen probes were
inserted into the beakers and data collecting began.
Plants were then left in the controlled setting for a onehour
period. Oxygen production rates were measured
in mg/L by the data logger device. At the conclusion of
each test period, the maximum, minimum, and average
oxygen production levels were recorded. A total of four
tests were performed for each solution group.
Results
Oxygen production by S. virginica was
observed with all groups throughout the experimental
Oxygen Production (mg/L)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
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Saddleback Journal of Biology
Spring 2008
period. The highest oxygen production levels were
collected from the plants in the 3.5% saline groups,
with the 0% groups having the next highest production
levels (Fig. 1). The average oxygen production levels
were 0.52 ± 0.020 mg/L in the 0% solution, 0.69 ±
0.059 mg/L in the 3.5% solution, and 0.28 ± 0.053
mg/L in the 6.0% solution (Fig. 2).
The photosynthetic rates for the plants in the 3.5%
and the 0% saline solutions increased at a higher rate
throughout the one-hour period than the 6.0% saline
group (Tab. 1). Although the 6.0% saline groups had
lower oxygen production than other groups, none of the
plants showed evidence of decreased photosynthetic
rates or any signs of damage.
0
Oxygen Production (mg/L)
in
the
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Salinity
\when exposed to
various saline
solutions.
0%
Oxygen
production
3.50%
6.00%
Figure 1. Oxygen production (mg/L) of S. virginica when
exposed to various saline solutions. Squares represent
line for groups in 3.5% salinity; triangles represent
groups in 0% salinity; and circles represent groups in
6.0% salinity.
levels were 0.52 ± 0.020 mg/L in 0%
salinity,
0.69 ±
0.059 mg/L in the 3.5%
solution, and 0.28 ± 0.053 mg/L
0 5 10 15 20 25 30 35 40 45 50 55 60
Time, min.
Figure 2. Average oxygen production (mg/L) ±S.E.M. of
four test groups of S. virginica when exposed to various
saline solutions. Oxygen production levels were 0.52 ±
0.020 mg/L in 0% salinity, 0.69 ± 0.059 mg/L in the
3.5% salinity, and 0.28 ± 0.053 mg/L in 6.0% salinity.