Saddleback Journal of Biology - Saddleback College

Spring 2010 Biology 3B Paper
Average Percentage of Stomata Open
100.00%
80.00%
60.00%
40.00%
20.00%
0.00%
-20.00%
0% 33% 75% 100%
Humidity Level
Figure 2. Mean percentages of stomata opened for
each humidity. There was no significant difference
stomatal response and humidity (p=0.292, ANOVA).
Error bars indicate mean ± SEM.
Discussion
The results of the study reject the hypothesis
as there was no statistical significant difference
between carbon dioxide levels and stomatal response
in relation to humidity. However, further research
suggests that humidity does in fact play a role in
stomatal response and can affect carbon dioxide
fixation (Lange and Medina, 1979; Griffiths et al.,
1986; Luttge et al., 1986).
A study done by Herppich (1997) proposed
that stomata do respond to humidity levels; however
stomatal reaction was not absolutely linked to carbon
dioxide consumption at night in Plectranthus
marrubioides. The research showed that drought
stress played a large role in the plant’s ability to
fixate carbon. When P. marrubioides was well
watered, there was no link between carbon dioxide
uptake and stomatal response in relation to humidity.
However, in extreme drought situations, humidity
levels did affect carbon dioxide consumption
(Herppich, 1997).
Guard Cell Turgidity
Stomatal opening is caused by turgidity
within the guard cells; the more turgid the guard
cells, the more open the stomata. Turgidity is
determined by an influx or efflux of ions
(MacRobbie, 2006). The movement of ions follows
an osmotic gradient in which the guard cells must
uptake water to become turgid. The influx of water
and ions into the guard cell vacuole creates pressure
and the stomata opens (Sheriff & Meidner, 1975).
Since the leaves were removed, it is likely that there
may have been a decrease in the overall water content
within each leaf over the six hour period. Upon
reweighing the leaves after six hours, they appeared
to have a decrease in weight. If this weight loss was
due to water loss, the guard cell vacuoles could not
reached sufficient osmotic pressure to become turgid
and fully open the stomata.
Acclimation
Although the leaves were acclimated for
three hours, it is possible that this acclimation time
was not sufficient. In other studies, plants were
acclimated for a minimum of two weeks prior to any
data collection (Hartsock & Nobel, 1976). Upon the
introduction of an environmental shift, CAM plants
take longer periods of time to show any significant
physiological changes (Szarek, et al. 1987).
Leaf Age
Another factor that may have influenced the
data was the age of the leaves. A study done by
Jones (1974) showed that leaf age contributed to
carbon dioxide exchange in Bryophyllum
fedtschenkoi, a CAM plant. Young B. fedtschenkoi
leaves did not perform CAM and produced carbon
dioxide during the night. However, mature leaves did
perform CAM. It was suspected that the mature
leaves had more vacuole space and were thus able to
store higher quantities of carbon dioxide. Although
the leaves used from D. lanceolata were all the same
length, it is possible that there was variation in leaf
age.
Although the data did not conclude with a
significant difference, it might be beneficial for
future studies to allow for a greater acclimation time
prior to data collection. Other areas of interest could
include monitoring changes in pH and soil water
potential.
Literature Cited
Black, C.C. and Osmond, C.B. (2003). Crassulacean
acid metabolism photosynthesis: ‘working the night
shift.’ Photosynthesis Research, 76, 329-341.
Cushman, J.C. (2001). Crassulacean acid
metabolism. A plastic photosynthetic adaptation to
arid environments. Plant Physiology, 127, 1439-
1448.
Griffiths, H., Luttge, U., Stimmel, K.H., Crook, C.E.,
Griffiths, N.M., and Smith J.A.C. (1986).
Comparative of ecophysiology of CAM and C 3
bromeliads. III. Environmental influences on CO 2
assimilation and transpiration. Plant, Cell, and
Environment, 9, 385-393.
Hartsock, T.L. and Nobel, P.S. (1976). Watering
converts a CAM plant to daytime CO 2 uptake.
Nature, 262,574-576.
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Saddleback Journal of Biology
Spring 2010