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Abstract: 【Objective】The objective of this study was to investigate the salt tolerance of Chinese Iris (Iris lactea Pall. var. chinensis (Fisch.) Koidz.) and the osmoticum in leaves at different levels of exogenous nitrate, to provide a scientific basis for cultivation and management of Iris lactea. 【Method】 Seedlings in sand culture experiment were treated with nine cross combinations of different NaCl concentrations at 0.1, 140, and 210 mmol?L-1, and three nitrate nitrogen levels at 0.25, 4 and 8 mmol?L-1, respectively. After 35 d of treatment, biomass of leaf and root, uptake of mineral elements and the main osmoticum in leaves were determined.【Result】NO3- at 8 mmol?L-1 caused a much higher increase in leaf biomass than 4 mmol?L-1 nitrate at 140 mmol?L-1 NaCl treatment. The exogenous nitrate (4 and 8 mmol?L-1) caused a 30% increase in leaf biomass at 210 mmol?L-1 NaCl, compared to the values at 0.1 mmol?L-1. No differences in leaf biomass were observed between two nitrate concentrations (P＜0.05). Exogenous nitrate resulted in a decrease in root/shoot ratio and leaf membrane permeability but an increase in total N of leaf and root under NaCl stress, while it had no significant effect on mineral element contents (K+、Na+、Ca2+、Mg2+). Contents of inorganic ions in leaves under interactions of nitrate and NaCl was Cl-＞K+＞Na+＞NO3-. Increase in concentrations of exogenous nitrate caused a decrease in Cl-, Na+ and K+ contents but an increase in proline and NO3- contents.【Conclusion】The growth under NaCl stress was improved by exogenous medium concentration of nitrate, and the mechanism may depend on improvement of nutrient uptake under NaCl stress, increase in proline and NO3- and decrease in root/shoot ratio, Cl-, Na+ and K+ contents.

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