Photosynthetic response of three aquatic species of Schoenoplectus (Reichenb.) Palla under salt stress

The experiment was conducted to evaluate physiological and anatomical modification in response to sat tolerance three halophytic species of Schoenoplectus (Reichenb.) Palla. Plants were collected from three different sites were grown in non-aerated hydroponic conditions. Four levels of NaCl, 0, 100, 200 and 300 mM, were maintained in solution culture to investigate the response of growth and photosynthesis to salt stress. Schoenoplectus triqueter showed optimal growth at 100 mM NaCl and better photosynthetic response to salt stress than that recorded in the other two species (S. lacustris and S. juncoides). Net CO2 assimilation rate (A) of S. juncoides remained unaffected up to 200 mM NaCl, but thereafter at 300 mM NaCl it decreased drastically. In contrast, in S. triqueter, CO2 assimilation was found to be stimulated at 100 and 200 mM NaCl, whereas such stimulation in net CO2 assimilation in S. lacustris was found only at 100 mM NaCl. Transpiration rate decreased in S. lacustris and S. triqueter with increasing salt stress, whereas in S. juncoides it increased at all salt levels. Stomatal conductance decreased in all three species at 300 mM in. Water use efficiency (WUE=A/E) in S. triqueter increased with increase in external salt concentration of the three Schoenoplectus species. Schoenoplectus triqueter was more efficient in controlling stomatal movement. The dominant anatomical traits related to S. triqueter (the most tolerant among all species) were found to be stomatal size, shape, and density, high water use efficiency, low transpiration rate, and low reduction in photosynthetic rate and chlorophyll pigments. Moreover, stomata were oriented in distinct grooves.