Abstract: Species-area relationships (SARs) were discussed in the past decades, and they were supposed to be one of the few "genuine law" in ecology. Xinjiang is located in the hinterland of the Eurasia, where there is a high radiation but a low precipitation. In this study, the patterns and mechanisms of SARs in different arid vegetation types in the Tianshan Mountains were explored by investigating sample plots. The species-area curves of steppe, meadow and desert were charted based on 26 nested sample plots, the minimum area of each nested sample plot was 0.25 m², and the maximum one was 400 m². All species in each sub-plot were recorded to develop SARs. The logarithmic form power curve (S = c·A^z) was applied to fit SARs, and then SARs from different areas were compared with climatic variables by plotting the slope (z value) and intercept (c value) to explore the main factors affecting the patterns of SARs in Xinjiang. The power-law model was used to explain 0.90 ± 0.01 of variance of species richness at different scales. The average value of overall slope was 0.20±0.02, lower than the mean of the world. The slopes of steppe and meadow were 0.13±0.01 and 0.14±0.02 respectively. There was no significant difference between the two vegetation types. However, these two figures were significantly lower than that of desert (0.28±0.02). The climatic variables were classified into three groups: energy, water and climatic stability. In the full climatic models, all the factors were used to explain 80.42% of z value and 91.90% of c value respectively. In all the three factors, water factor was the most important for SARs, and the R² values of z and c were 69.88% and 66.22% respectively. However, the effects of water factor on z value and c value were quite different, and z value was decreased but c value was increased with the increase of water factor. Similarly, z value was decreased but c value was increased with the increase of species richness. The results reveal that water was the main factor affecting the species-area relationship in this area, and the species richness also played an important role.

Key words: steppe, meadow, desert, biodiversity, moisture cointent, species richness, Tianshan Mountains, Xinjiang