Photosynthetic and growth responses of cattail ( Typha domingensis) and sawgrass ( Cladium jamaicense) to soil redox conditions

Abstract

Under controlled laboratory conditions, cattail ( Typha domingensis Pers.) 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 both species, light saturation was not achieved at the highest photon irradiance of 1100 μmol m −2 s −1. Sawgrass showed greater photosynthetic capacity per unit area of leaf at higher irradiances than cattail. However, light compensation points were estimated at 25 and 60 μmol m −2 s −1 for cattail and sawgrass, respectively. In both species, stomatal conductance was reduced significantly in response to the lowest Eh condition (−200 mV). Net photosynthesis decreased significantly in both species in response to the reduced Eh conditions, but there were differences. The reductions were proportionally greater in sawgrass than in cattail. Thus, at −200 mV Eh, net photosynthesis was reduced by 71% for cattail; while in sawgrass there was no net photosynthesis, only respiration. Cattail showed significantly greater net photosynthetic rates as compared with sawgrass at the lowest Eh treatment (−200 mV). Although total biomass was reduced in both species in response to low Eh conditions, it nevertheless was significantly greater in cattail than sawgrass under 0 and −200 mV soil Eh treatments. However, the biomass allocation pattern did not differ between the two species across treatments. Results of the present study support the hypothesis that in both species differences in pattern of site occupancy and competition under low soil oxygen conditions may be partially explained by differences in their photosynthetic characteristics and photosynthetic acclimation to oxygen-deficient environments.