Ecophysiological responses of the salt marsh grass Spartina maritima to salinity

The effects of salinity on growth and productivity of Spartina maritima (Curtis) Fernald were investigated in glasshouse and field experiments in 2008. In the glasshouse study, plants were subjected to 2%, 10%, 20%, 40% and 80% sea water, with tidal simulation, for 10 months. Increase in salinity from 2% to 20% sea water increased biomass accumulation, CO2 exchange, quantum yield of Photosystem II (PSII), electron transport rate (ETR) through PSII, and intrinsic photochemical efficiency of PSII, while further increases in salinity to 80% resulted in significant decreases in these parameters. Concentrations of proline increased significantly with increase in salinity up to 80% sea water. In the field study, soil physicochemical conditions between streamside and inland sites were compared, and the constraints imposed by any differences on plant ecophysiological responses determined. At the inland site, soil water potential (Psi), electrical conductivity of the soil, total cations, and the concentrations of Na+, Ca2+, Mg2+ and P, were significantly higher than those of the streamside site, while CO2 exchange, quantum yield of PSII, ETR through PSII, and intrinsic photochemical efficiency of PSII were significantly lower. The results suggest that S. maritima grows optimally at a salinity of about 20% sea water, and that higher salinity decreases growth and photosynthetic performance.