The effects of climate change could severely impact coastal ecosystems, in particular the exposure of endemic wetland plants to increased and highly variable salinity levels. Bald cypress (Taxodium distichum) is a common tree species found along the southeastern Atlantic coast, and is considered a keystone and foundational species in freshwater forested wetlands. The objective of the present study was to observe the ecophysiological response of Bald cypress to the type of salinity exposure that occurs during storm over-wash events. More specifically, our goal was to determine how increased salinity could alter basic ecophysiological processes such as photosynthesis and water relations that could lead ultimately to inhibited growth and reproduction. Individuals were separated into two groups, a control group exposed to artificial freshwater (0 ppt NaCl, plus other salts) and an experimental group receiving more brackish freshwater (5 ppt), for a period of 4 weeks. Measurements of plant water status, photosynthetic pigment concentrations and photosystem II function (via fluorimetry) were taken from both groups to determine potential effects on photosynthesis. Pigment extractions indicated that chlorophyll a, chlorophyll b, and carotenoid levels declined in plants exposed to higher salinity compared to control plants. In contrast, fluorimeter readings of both groups indicated healthy photosystems (Fv/Fm > 0.74), while plant water potential measurements indicated an increase in water stress in the salt treatment versus control group. Overall, these data point to a potentially negative responses in photosynthesis and, thus, growth in T. distichum with greater exposure to saltwater over-wash. Thus, the native freshwater wetlands of these coastal communities appear vulnerable to salt water incursion associated with greater storm activity and sea level rise.

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Figure 1: The mean concentration of chlorophyll a/b and carotenoids (photosynthetic pigments) present in Taxodium distichum leaves for the control and treatment groups (error bars show ± standard deviation).

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Figure 2: The mean fluorometer readings (Fv/Fm ratio) for the control and treatment groups (error bars show ± standard deviation). Higher values near 1.0 indicate a healthier photosystem for generating the high energy compounds needed for the carboxylation reactions of photosynthesis.

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Figure 3: The mean predawn leaf water potentials for the control and treatment groups (error bars show ± standard deviation). Predawn values indicate the maximum hydration level to begin the day and before stomatal opening begans the characteristic drop in water status that continues during the day while stomata are open.