Optimal exogenous calcium alleviates the damage of Snow-melting agent to Salix matsudana seedlings

As the main component of snowmelt agents, NaCl is widely used in northern winters and significantly impacts the expected growth of garden plants in north China. Salix matsudana is also faced with salt stress caused by snowmelt, which seriously affects its development as the main tree species in the northern landscape. However, how exogenous calcium alleviates salt stress in Salix matsudana is not yet clear. In this study, the indicators of growth indices, photosynthetic characteristics and stress resistance were measured by hydroponic assays in combination with three NaCl conditions (0, 50 and 200 mmol·L -1 ) and five calcium concentrations (0, 2.5, 5, 10 and 20 mmol·L -1 ). The study’s results indicated that the application of exogenous calcium remarkably promoted the growth of Salix matsudana seedlings under NaCl stress. When the exogenous calcium concentration was 10 mmol·L -1 , the plant height and basal diameter of Salix matsudana seedlings increased significantly, and the biomass of all parts reached the maximum ( P< 0.05). Exogenous calcium can substantially improve the photosynthesis of Salix matsudana seedlings under salt stress. The photosynthetic parameters, photosynthetic pigment content and photosynthetic product synthesis of Salix matsudana seedlings were significantly increased at an exogenous calcium concentration of 10 mmol·L -1 , and the photosynthetic level of Salix matsudana seedlings reached the highest value. The chlorophyll fluorescence parameters ( F v /F m , F v /F 0 ) of Salix matsudana seedlings were significantly decreased under different concentrations of NaCl stress. The maximum photochemical efficiency ( F v /F m ) and potential photochemical efficiency ( F v /F 0 ) of Salix matsudana seedlings peaked when the exogenous calcium concentration was 10 mmol·L -1 , which was significantly higher than that of the other treatments ( P< 0.05). The water use efficiency of Salix matsudana was affected considerably by NaCl stress. The WUE and iWUE peak values of Salix matsudana were significantly higher than those of other calcium concentrations at 10 mmol·L -1 ( P< 0.05). Exogenous calcium can increase the activities of CAT, SOD and POD enzymes in Salix matsudana seedlings under different NaCl concentrations. Under NaCl stress, adding exogenous calcium promoted the survival rate and growth of Salix matsudana seedlings. In conclusion, the optimum exogenous calcium concentration for Salix matsudana seedlings was 10 mmol·L -1 . High or lo