Abstract: Anitrogen addition experiment was performed at the Department of Agriculture Environmental Science Experiment Station in Nagqu town, Northern Tibet, from 2015 to 2016. Urea solution was sprayed on each replicated plot using five treatments: 0 g·m^-2 (CK), 7 g·m^-2 (N₁), 15 g·m^-2 (N₂), 30 g·m^-2 (N₃), 40 g·m^-2 (N₄), 50 g·m^-2 (N₅). The study focused on the response of Elymus nutans leaf functional traits and population characteristics to these different nitrogen application rates. The results showed: 1) The leaf area and specific leaf area of E. nutans increased with nitrogen application. Nitrogen application also significantly increased tiller number (P<0.05), while the leaf photosynthetic rate showed no significant response; 2) Under different nitrogen treatments, tassel density increased to some extent but the reproductive height was not significantly impacted. The trophic height increased significantly (P<0.05); the largest increase was 32.87 cm at N₅, 111.29% higher than CK. Coverage increased rapidly at first and then stabilized in the saturated state, rising from 43.67% to 100%. With increasing nitrogen rates, biomass increased significantly (P<0.05), and the higher the nitrogen the higher the biomass, with the largest increase occurring in the N₅ treatment, 303.18% (587.89 g·m^-2) higher than the control group (145.81 g·m^-2); 3) Correlation analysis showed that there was a significant correlation between the biomass and reproductive height, trophic height, and coverage when loaded on nitrogen application as a single factor (P<0.01). These results indicate that population characteristics rather than leaf functional traits are the key factors to improve the productivity of E. nutans grassland undergoing nitrogen application.

Key words: Northern Tibet, Elymus nutans, nitrogen level, functional traits, population characteristics, productivity