Abstract: The distribution patterns of plant diversity in the Qinghai-Tibet Plateau vary across spatial scales. However, the factors that drive these patterns are still unclear. We investigated plant community and soils in 33 grassland sites along a precipitation gradient from Qinghai-Tibet Plateau, and elucidated the patterns of plant species diversity from three aspects: α, β, and γ diversity. Linear regression and structural equation modeling (SEM) were used to explore the direct or indirect factors affecting the distribution patterns of plant diversity. We found that α diversity and γ diversity increased, while β diversity decreased with increasing precipitation. Increased precipitation enhanced α diversity directly by changing soil moisture and indirectly by increasing soil inorganic nitrogen content. Moreover, increased precipitation indirectly increased γ diversity by increasing soil N/P ratio and decreasing soil pH. In summary, changes of precipitation can alter soil physicochemical properties, and thus affect plant diversity at different spatial scales.

Key words: precipitation pattern, environmental factor, plant diversity, soil physicochemical property, spatial scale, Qinghai-Tibet Plateau