Calcium alleviates decreases in photosynthesis under salt stress by enhancing antioxidant metabolism and adjusting solute accumulation in Calligonum mongolicum

Calcium is known to affect photosynthesis under normal conditions and induces tolerance in plants to biotic and abiotic stresses through influencing physiological processes. In this study, physiological processes were investigated in the desert plant Calligonum mongolicum to examine how these processes were induced by calcium treatments to alleviate a decrease in photosynthesis under salt stress. Salinity decreased biomass and photosynthesis, regardless of the salt stress level, but increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activity and decreased malondialdehyde (MDA) content under 4 and 8 g/L NaCl and decreased all enzyme indices under 16 g/l NaCl stress. The plants with 5 and 10 mM added calcium had significantly greater biomass and photosynthesis than plants with the non-calcium application or calcium application with 20 mM at all salinity levels. Calcium-treated plants exhibited increases in photosynthesis and biomass along with higher levels of SOD, POD, CAT, APX, GR and total soluble sugar, and lower levels of MDA and proline. Alleviating the effects of salt stress on photosynthesis depended on the concentration of calcium used. Maximum alleviation of salt stress occurred with 5 and 10 mM calcium application. Our result indicated that calcium could be used in forestation and restoration of C. mongolicum in high saline soil.