Conclusions
In this study, we found that both aboveground plant biomass and SOC increased with increasing plant species richness. Plant species richness had greater effects on SOC than on aboveground biomass. Aridity and overgrazing decreased aboveground plant biomass and SOC through decreasing plant species richness, whereas haying had less detrimental effects on ecosystem functions and enhanced plant diversity. Together, the results demonstrated that climate change and grazing mainly threaten soil carbon storage in a synergistic way via their detrimental effects on plant diversity. However, the study also shows that certain management types like haying can maintain plant diversity and soil carbon storage. Moreover, the beneficial effects of plant diversity are particularly important in arid environments. Therefore, grassland management should be adapted to ongoing global climate change.