Climate factors impact different facets of grassland biodiversity both directly and indirectly through soil conditions

Context Climate and soil factors play central roles in shaping grassland landscapes. However, an accurate assessment of how these factors influence grassland plant diversity has been scarce and difficult because soil properties are determined partly by climate factors, and diversity can be characterized in variety of ways. Objective We aimed to explore how and to what extent climate and soil factors influence different components (richness vs. evenness) and levels (among- vs. within-species) of plant diversity. Methods We used the linear and the structural equation models to examine the impacts of 16 soil and climate factors on the four diversity indices across 113 Qinghai-Tibetan grassland sites. Results Species richness was negatively correlated with sunshine hours, temperature and soil pH, but positively with soil fertility and climate moisture (precipitation and relative humidity). By contrast, Pielou evenness and individual size inequality (ISI) were correlated positively with temperature, but negatively with soil fertility and climate moisture. The main factor affecting species richness and Shannon diversity directly (or indirectly through soil pH and total nitrogen content) was precipitation, whereas precipitation and temperature together governed ISI. Moreover, total soil nitrogen (or phosphorus) content was the significant factor increasing (or decreasing) ISI. Conclusion Results suggest that moisture conditions, especially precipitation, are the main driver of landscape-scale biodiversity. We also highlight the importance of both direct and indirect climate impact on grassland community assembly through changing soil conditions.