Soil Microbial Communities Adjust Thermal Traits and Carbon Allocation in Response to Climate Manipulations in...

Soil microorganisms regulate carbon (C) cycling, and their growth and respiration are strongly dependent on temperature. Yet it remains unclear how warming alters microbial thermal traits, community structure, and the balance between microbial respiration and growth, particularly in subtropical ecosystems where high temperatures coincide with low soil moisture, potentially constraining microbial activity. In this study, we investigated soil microbial thermal traits for growth and respiration, and the microbial community composition in two subtropical land-uses with contrasting microclimates: a cooler, moist pristine forest and a warmer, drier cropland. Using open top chambers (OTCs) or rain exclusion shelters over 1.5 years, we quantified how experimental warming and drought altered microbial functioning and upscaled these effects using field soil temperature and moisture records. Field warming increased the abundance of warm-adapted bacterial and fungal taxa and led to shifts in microbial thermal trait distributions toward higher minimum temperature values for microbial growth, indicating community-level thermal adaptation. These thermal trait adaptations resulted in a modeled 36% reduction in annual soil CO₂ efflux in warmed plots. Overall, our results show that thermal trait adaptation, driven partly by community restructuring, buffers soil C losses under warming and may enhance soil C sequestration in subtropical ecosystems. These findings showcase the importance of integrating microbial thermal traits into soil C models to improve predictions of climate-carbon feedbacks.