Table 1. Concluded. 



12% and 18%. This finding indicated that, in addition to diffusional limitations, photosynthetic 

 capacity was reduced through metabolic factors (Pezeshki et al. 1987e). 



In Scirpus olneyi plants, salinities of 7 ppt and 10 ppt caused immediate reduction in carbon 

 fixation (Meeder et al. 1989). Nevertheless, in this species, some photosynthetic recovery was 

 noted in all treatments including those plants which survived the 10-ppt saltwater treatment. This 

 recovery indicated that some photosynthetic acclimation occurred in this species especially at these 

 salinity concentrations. 



Many tree species respond to soil flooding by stomatal closure and reduction of net 

 photosynthesis (Kozlowski and Pallardy 1979; Newsome et al. 1982; Tang and Kozlowski 1982; 

 Zaerr 1983; Pezeshki and Chambers 1985a,b). However, few studies have been conducted to 

 assess carbon assimilation responses of bottomland tree species to saltwater intrusion. Coastal 

 tree species are more susceptible to salinity than flooding alone or there may be a synergistic 

 effect of combined flooding and salt on photosynthetic process. In Fraxinus pennsylvanica seedlings, 

 carbon assimilation rates declined following salt application in the absence of flooding. Net carbon 

 assimilation was reduced as much as 86% in response to soil salinity. The study demonstrated the 

 high level of sensitivity of green ash, a flood-tolerant species, to soil salinity; however, it did not 

 examine the effect of combined stresses and their possible interaction on carbon assimilation rates 

 of this species. Recent studies on baldcypress (Taxodium distichum) seedlings showed a 58% to 

 84% reduction in net assimilation rates when plants were exposed to saline water which contained 

 salt concentrations in the range of 2 to 7 ppt (Pezeshki et al. 1986, 1987a). The impact was 

 evident for all salinity levels and was closely related to the salinity of flood water (Table 1). In 

 an experiment conducted on tupelo-gum (Nyssa aquatica) seedlings, it was found that floodwater 

 containing 3 ppt salt caused substantial reduction in net assimilation throughout the day, and the 

 effects persisted for the entire 12 weeks of the experiment. Furthermore, the interaction of salt 

 and flooding was significant (Pezeshki et al. 1988a). 



Although the gas exchange rates are different depending on the species, leaf age, and the time 

 of measurement during a growing season, diurnal patterns for non-stressed plants appear to be 

 similar in marsh plants. Generally, saltwater intrusion causes stomatal closure as well as reduction 

 of carbon assimilation rates throughout the day, altering normal gas exchange patterns, and 

 consequently reducing the net diurnal carbon Fixation (Pezeshki et al. 1986, 1987a, b, c, d, e). 



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