Abstract: This work is to explore the regulation effect of root application of salicylic acid（SA）eliminating salt stress damage to tomato seedlings,and to provide scientific basis for rational use of SA to solve salt damage in tomato cultivation and breeding salt-tolerant tomato varieties. Under the condition of nutrient solution cultivation,a hydroponic experiment was conducted to explore the effects of different concentrations（50,100,200,400,and 800 μmol/L）exogenous SA on plant growth,chlorophyll content,gas exchange,chlorophyll fluorescence parameters,membrane peroxidation,and antioxidase activity in tomato cultivar（‘Qinfeng Baoguan’）seedlings under stress of 100 mmol/L NaCl. The results showed that the growth inhibition of tomato seedlings under salt stress was effectively alleviated after treated with different concentrations of SA. Meanwhile,the chlorophyll content,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）,maximum fluorescence of leaves（Fm）,PSII maximum photochemical efficiency（Fv/Fm）,actual photochemical efficiency（Φ_PSII）,and photochemical quenching coefficient（qP）increased to varying degrees,while intercellular CO₂ concentration（Ci）,minimum fluorescence Fo and non-photochemistry quenching coefficient（NPQ）significantly decreased. The amplitude of each index reached the maximum especially when the concentration of SA was 200 μmol/L. When tomato seedlings were put under salt stress,the superoxide dismutase（SOD）,peroxidase（POD）activity,malondialdehyde content,and electrolyte exudation rate of theirs leaves raised remarkably,while their catalase（CAT）activity did not change so obviously. Application of exogenous SA treatment at various concentrations promoted the increase of the three enzyme activities above,along with making the leaf malondialdehyde content and electrolyte exudation rate markedly reduced;moreover,the change was the most significant when treated with 200 μmol/L SA. Studies have demonstrated that exogenous SA could relieve the oxidative damage caused by salt stress mainly by enhancing the photosynthetic capacity of seedling leaves,hence improving the salt tolerance of tomato plants. The treatment with 200 μmol/L SA showed the best results under the experimental conditions,.

Key words: salicylic acid, salt damage, tomato, gas exchange, chlorophyll fluorescence, antioxidase