Abrupt shifts in the plant species richness and community composition along an aridity gradient in the Mongolian grasslands

Aridification is a major facet of climate changes in drylands. However, little is known about the shifts in the plant community composition to aridity. Dryland grasslands are widely used for livestock grazing. Although grazing impacts can be relatively small in arid regions, overgrazing has great impacts on vegetation, regardless of aridity. Thus, investigations under long-term grazing exclusion are suitable to clarify the response of composition to aridity without confounding effect of grazing. We investigated the shifting patterns in species richness and composition with grazing exclosure along a broad range of aridity (0.6–0.95) in Mongolia. The shifts in the species richness and composition (the axis of NMDS) were investigated by model selection for GLMs, including the linear and quadratic terms of aridity, and soil environments. The best models included both the linear and quadratic terms of aridity, which showed nonlinear and unimodal responses to aridity. Particularly, their shifts were relatively abrupt at high aridity, which might be attributed to environmental filtering by aridity and competitive exclusion by aridity specialists. Our study firstly demonstrated the nonlinear shift of plant community composition to aridity, indicating the vulnerability of plant communities to press changes of aridity, especially in highly arid regions. Highlights Patterns in plant species richness and composition in Mongolian steppe were studied Shifts in species richness and community composition were nonlinear along an aridity gradient abrupt at high aridity Nonlinear shift indicates the vulnerability of plant communities to changes in highly arid regions