Climate warming suppresses soil abundant fungal taxa and reduces soil carbon efflux in a semi-arid grassland

The abundance, diversity and activity of soil microorganisms critically control the fate of recent plant carbon (C) inputs as well as protecting soil organic C, regulating C-climate feedbacks. However, the effects of climate change drivers such as warming and precipitation change on soil microbial communities and C dynamics remain poorly understood. Utilizing a long-term field warming and precipitation manipulation in a semi-arid grassland on the Loess Plateau and a complementary incubation experiment, here we show that warming and rainfall reduction differentially affect the abundance and composition of bacteria and fungi, and soil C efflux. Warming significantly reduced the abundance of fungi but not bacteria, increasing the relative dominance of bacteria in the soil microbial community. In particular, warming shifted the community composition of abundant fungi in favor of oligotrophic Capnodiales and Hypocreales over potential saprotroph Archaeorhizomycetales . In contrast, precipitation reduction increased soil microbial biomass, but did not significantly affect either the abundance or diversity of bacteria. Furthermore, soil abundant, not rare, fungal community composition was significantly correlated with soil CO2 efflux. Our findings suggest that alterations in the fungal community composition, in response to changes in soil C and moisture, dominate the microbial responses to climate change and thus control soil C dynamics in semi-arid grasslands. Impact statement Semi-arid grasslands play a critical role in global carbon (C) cycle and potential feedbacks to climate change. Understanding the responses of soil microorganisms to warming and rainfall change is key to evaluating and predicting semi-arid grassland soil C dynamics under future climate change scenarios. Our study showed that warming induced a shift in the abundant fungal community, favoring oligotrophic fungi (i.e., Capnodiales and Hypocreales ) over the potential saprotrophic Archaeorhizomycetales, and reduced C efflux. These findings advance our understanding of soil microbial and C responses to climate change drivers and may help predict and possibly manage soil C sequestration in semi-arid grasslands. ### Competing Interest Statement The authors have declared no competing interest.