The plasticity of the photosynthetic apparatus and antioxidant responses are critical for the dispersion of Rhizophora mangle along a salinity gradient

The physiological mechanisms responsible for salinity tolerance in Rhizophora mangle remain unclear. Moreover, the effects of climate change on the distribution and abundance of mangrove forests are unknown. Thus, to elucidate the possible factors responsible for saline tolerance in this species, we investigated the growth and physiological parameters in young plants cultivated in a saline gradient (0, 10, 35, and 70 ppt). Biometric indicators, water status parameters, cell integrity, ions concentrations in leaves and roots, pigment concentrations, chlorophyll a fluorescence, oxidative stress indicators, and antioxidant enzyme activities were evaluated. The results showed that R. mangle could grow in the absence (0 ppt) or moderate salinity (10 ppt). However, by increasing the salinity to sea level (35 ppt), the growth and development decreased compared to plants grown at ten ppt. In hypersalinity (70 ppt), plant growth and development are severely hampered. Under hypersalinity, the increased concentration of H2O2 promoted lipid peroxidation and membrane damage. The chlorophyll contents decreased, and accessory pigment concentrations increased. Moreover, the modulation of the quantum yield of PSII and the antioxidant system was crucial to avoiding photoinhibition and salinity tolerance in R. mangle.