Physiological Responses of Enhalus Acoroides to Osmotic Stress

AbstractThis study aims to examine photophysiological and osmotic responses in seedlings of the seagrassEnhalus acoroidesafter exposure to different salinity levels. Seagrass seedlings were grown for 20 days in control (salinity 30), hyposaline (salinity 10 and 20) and hypersaline (salinity 40 and 50) conditions. The present study showed that both hypo- and hypersaline conditions affected the photophysiology ofE. acoroidesseedlings, reducing the maximum quantum yield of photosystem II (Fv/Fm) and total chlorophyll content. The photosynthetic system appeared to be more sensitive to hyposaline than to hypersaline conditions as shown by immediate declines inFv/Fmand total chlorophyll content. Hyposaline conditions increased the water content in roots. The increase in tissue Na+content induced by hypersalinity did not affect photosynthetic integrity and was more pronounced in leaves than in roots. It is concluded that the ionic homeostasis ofE. acoroidesseedlings is less affected by short-term hypersalinity than by hyposalinity. The K+/Na+ratios in leaves with hypersalinity decreased by 20 days after treatment. Additionally, the photosynthetic efficiency (Fv/Fmand total chlorophyll content) is highly sensitive to salinity shifts and can be used as a marker for short-term acclimation to salinity stress in this seagrass species.