Abstract: The effects of nitrogen deposition on plant communities, especially on the alpine meadow with relatively fragile habitats, have been hot topic in ecology. To better understand the effects of nitrogen deposition on the eco-physiology of different plant functional groups in the alpine meadow of Qinghai-Tibetan Plateau, we conducted a field experiment under different nitrogen addition levels (0, 8, 24, 40, 56, 72 kg·hm^-2·a^-1) to simulate natural nitrogen deposition. We classified the plant species into three functional groups, including grass, sedge, and forb. Results showed that: (1) The effects of nitrogen deposition on three functional groups were different. Nitrogen addition increased the abundance and height of sedge, but had no effects on that of grass and forb (P>0.05). Aboveground biomass of grass showed non-linear response to nitrogen addition, while the aboveground biomass of sedge and forb significantly decreased with the increases of nitrogen addition level. (2) Net photosynthetic rate of grass showed nonlinear response to nitrogen addition, while that of sedge and forb significantly decreased with the increases of nitrogen addition level. Nitrogen addition significantly increased the stomatal conductance (G_s) and transpiration rate (T_r) of all the three functional groups. (3) The net photosynthetic rate was significantly positively correlated with aboveground biomass of the three functional groups (P<0.05). In conclusion, short-term high nitrogen deposition will decrease the accumulation of plant aboveground biomass through reducing the photosynthetic capacity, and thus inhibiting plant growth in alpine meadow of Qinghai-Tibetan Plateau.

Key words: nitrogen concentration, fine root decomposition, microbial community composition, magnesium concentration