Objective To study the effect of spraying Salicylic acid (SA) with different concentration on the physiological metabolism of Ulmus pumila tissue-cultured plantlets under salt stress.

Method One-year-old U. pumila "Baiwa NO.1" plantlets were selected as materials and the effect of spraying different concentrations of SA (0, 0.5, 1.0, 2.0 mmol·L^-1) on the water physiology, membrane lipid peroxidation, photosynthetic pigment content and photosynthetic gas exchange parameters were studied under 0, 50, 100 and 150 mmol·L^-1 NaCl treatments.

Result (1) Exogenous SA improved the relative water content and soluble sugar content in leaves significantly, and decreased the MDA content, but it had no significant effects on the electrolyte leakage. (2) 0.5 and 2.0 mmol·L^-1 SA improved the chlorophyll a, chlorophyll b, carotenoid and chlorophyll a+b contents in the leaves of U. pumila under 50 and 100 mmol·L^-1 NaCl stress. And the effect of 1.0 mmol·L^-1 SA on the chlorophyll content under each NaCl concentration was not significant. (3) The net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci) and transpiration rate (Tr) increased significantly with the addition of 2.0 mmol·L^-1 SA under NaCl stress. The addition of 1.0 mmol·L^-1 SA decreased Pn and Gs significantly under each NaCl concentration.

Conclusion Appropriate SA concentration can alleviate the physiological parameters of U. pumila under salt stress. The results of comprehensive evaluation using the subordinate function method show that 0.5 and 2.0 mmol·L^-1 are the optimal concentration of SA.