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

Soil microorganisms critically affect the ecosystem carbon (C) balance and C-climate feedback by directly controlling organic C decomposition and indirectly regulating nutrient availability for plant C fixation. However, the effects of climate change drivers such as warming, precipitation change on soil microbial communities, and C dynamics remain poorly understood. Using 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. Also, precipitation reduction increased soil total microbial biomass but did not significantly affect the abundance or diversity of bacteria. Furthermore, the community composition of abundant, but not rare, soil fungi 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. Semi-arid grasslands play a critical role in the global carbon (C) cycle and C-climate feedback. Understanding the responses of soil microorganisms to warming and rainfall change is key to evaluating and predicting soil C dynamics in semi-arid grasslands 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.