Abstract: Both carbon (C) and nitrogen (N) are essential nutrients for plants. Their interaction and relationships with habitats influence growth, development, and nutrition status of plants. C∶N ratio of vegetation reflects growth rate of plants. Plant C and N concentrations, C∶N ratios and their relationships with environmental factors were analyzed based on the investigation of 58 sampling sites in a northern Tibet alpine grassland. The results showed that: (1) The coupling relationships between plant C and N varied in the alpine grassland. Plants could be divided into two groups: one with higher C∶N and another with lower C∶N. (2) The mean values of plant C concentration, N concentration and C∶N ratio in northern Tibet were 382.64 mg·g^-1, 17.76 mg·g^-1 and 22.24, respectively, with coefficients of variation (CV) in order of N concentration > C∶N ratio > C concentration. (3) For the plants with high C∶N ratio, different environmental factors explained by variance to plant C concentration, N concentration and C∶N ratio were in order of soil organic carbon (SOC) (48.91%) > soil total nitrogen (STN) (30.50%) > temperature (27.47%) > precipitation (16.66%). For plants with low C∶N ratio, the explanation variance was in order of precipitation (18.78%) > longitude (16.32%) > aridity index (AI, 14.35%) > plant species richness (12.58%). (4) For plants with high C∶N ratio, SOC concentration was negatively correlated with plant C and N concentration, and C∶N ratio was not significantly affected by other environmental factors. In contrast, for plants with low C∶N ratio, precipitation, longitude, AI and richness had significant negative effects on plant C concentration and C∶N ratio. This study provided scientific basis for sustainable utilization and ecological conservation and restoration of alpine grasslands in northern Tibet.

Key words: nitrogen reduction, carbon footprint, spring maize-late rice rotation, greenhouse gas emission