Abstract: Plant nutritional traits at the community-level are important drivers for several fundamental ecosystem processes. Effects of nitrogen deposition on the community-level stoichiometric characteristics are co-driven by interspecific variability (species turnover) and intraspecific trait variability (ITV; nutritional changes of each species). Hence, specifying the relative importance of those two processes is critically needed for predicting the alternations of ecosystem functioning. Based on a 6-year N addition experiment in a meadow steppe of Hulunbuir, we examined the relative contribution of those two processes to the changes of community-level N and P concentrations and N∶P stoichiometry in response to N enrichment. Results showed that plant community composition  significantly varied along the N addition rate gradient (from 0 to 50 g N·m^-2·a^-1). Out of the 17 examined species, eight species showed positive responses of N concentration to N inputs, while P concentrations and N∶P ratios in most species were not sensitive to N inputs. The community-level N concentration and N∶P ratio significantly increased with increasing N addition rates, while community-level P concentration remained unchanged. The N-induced alternations of community-level nutritional traits were mainly caused by ITV, which accounted for 75%-99%, 61%-91%, and 97%-100% of the total variation in community-level N concentration, P concentration, and N∶P, respectively. Our results indicated that (1) the responses of plant N∶P stoichiometry to N input were highly species-specific in the meadow steppe; and (2) while plant community composition and structure were quite sensitive to N inputs, changes of community-level nutritional traits were largely resulted from the ITV of a few dominant species.

Key words: community composition, ecological stoichiometry, intraspecific variation, nitrogen deposition, semi-arid grassland.