Abstract: Differences in leaf structure determine the intense competition for resources between C₃ and C₄ species under climate warming. Competitive advantage is not only reflected in photosynthetic rate, but also in the water and nitrogen content of the leaves. However, the competitive mechanisms between C₃ and C₄ species in temperate desert steppe under long-term warming remain unclear. Therefore, after six to eight years of warming (ambient temperature, the control treatment, warming 2 ℃ and 4 ℃, T1 and T2 treatments), we estimated the importance values of C₃ and C₄ species in the plant community, and monitored the photosynthetic rate, nitrogen and water content of plants and soil. Results showed that long-term warming increased the importance values of C₄ species in temperate desert steppe. Compared to the control treatments, the importance value of C₄ species increased by 29.30% and 26.97% in T1 and T2 treatments, respectively. Variation partitioning analysis and structural equation model showed that leaf photosynthetic rate had a non-significant effect on the distribution of C₃ and C₄ species. The proportion of C₃ and C₄ species in plant communities was mainly influenced by soil water and nitrogen content. In summary, this study suggests that the competitive advantage of C₃ species will be replaced by C₄ species under long-term warming. The nitrogen and water content in soils explain the distributional of C₃ and C₄ species in temperate desert steppe. CCEPTED MANUSCRIPT

Key words: climate warming, desert steppe, C₃ and C₄ species, plant functional traits, soil physical and chemical properties