The δ¹³C values of 51 plant species selected from eight plant communities along a moisture gradient were measured. Our results showed that all the community types that we investigated are dominated by C₃ species in the Xilin River Basin. Large variations in the average ¹³C natural abundance of different communities were detected, and the magnitude of δ¹³C values showed the following trend: typical steppe (–23.0‰) > degraded steppe (–23.5‰) > sand dune (–25.0‰) > restoring degraded steppe (–25.8‰) > meadow steppe (–26.4‰) ≥ saline meadow (–26.5‰) > swamp meadow (–28.2‰). The major determinants of the biomass-weighted δ¹³C values in a given community were the presence or absence of C₄ plants, the intrinsic variation among species and the variation of the same species growing in different habitats with different soil-moisture regimes and disturbance history. These results suggested that different habitats support dominant species with different water-use efficiencies and a trend in the community-level δ¹³C values was observed, as ascribed by the contribution of C₄ plants and/or the variations among species or the response of water-use efficiency of the same species to different soil moisture conditions.