PHOTOSYNTHETIC AND GROWTH-RESPONSES OF CATTAIL (TYPHA-DOMINGENSIS) AND SAWGRASS (CLADIUM-JAMAICENSE) TO SOIL REDOX CONDITIONS

Under controlled laboratory conditions, cattail (Typha domingensis Per s.) and sawgrass (Cladium jamaicense Crantz) were subjected to a range of soil redox potential (Eh) including +500, +250, 0 and -200 mV and plant photosynthetic activity and growth responses were measured. In b oth species, light saturation was not achieved at the highest photon i rradiance of 1100 mu mol m(-2) s(-1). Sawgrass showed greater photosyn thetic capacity per unit area of leaf at higher irradiances than catta il. However, light compensation points were estimated at 25 and 60 mu mol m(-2) s(-1) for cattail and sawgrass, respectively, In both specie s, stomatal conductance was reduced significantly in response to the l owest Eh condition (-200 mV). Net photosynthesis decreased significant ly in both species in response to the reduced Eh conditions, but there were differences, The reductions were proportionally greater in sawgr ass than in cattail. Thus, at -200 mV Eh, net photosynthesis was reduc ed by 71% for cattail; while in sawgrass there was no net photosynthes is, only respiration. Cattail showed significantly greater net photosy nthetic rates as compared with sawgrass at the lowest Eh treatment (-2 00 mV). Although total biomass was reduced in both species in response to low Eh conditions, it nevertheless was significantly greater in ca ttail than sawgrass under 0 and -200 mV soil Eh treatments. However, t he biomass allocation pattern did not differ between the two species a cross treatments. Results of the present study support the hypothesis that in both species differences in pattern of site occupancy and comp etition under low soil oxygen conditions may be partially explained by differences in their photosynthetic characteristics and photosyntheti c acclimation to oxygen-deficient environments.