Long‐Term Warming Reduces Bacterial Diversity and Functional Potential in Temperate Forest Soil

ABSTRACT Soil microbes are key regulators of forest carbon cycling, yet how their diversity and functional potential respond to long‐term warming remains poorly understood. Here, we report a five‐year in situ warming experiment in a temperate forest, combining ten repeated measurements of microbial diversity and functional gene potential, as well as continuous monitoring of soil CO 2 flux. We found that warming progressively reduced bacterial diversity and induced phylogenetically conserved community reorganization. Under warming, community composition shifted in a phylogenetically conserved manner. Warming generally reduced the abundance of microbial functional genes across most carbon‐, nitrogen‐, and phosphorus‐cycling gene categories, except for genes associated with starch decomposition. Warming also altered the factors associated with soil CO 2 flux: microbial diversity showed a stronger association with soil CO 2 flux under long‐term warming, whereas soil moisture was the dominant predictor in the control treatment. This warming‐enhanced biodiversity control over soil CO 2 flux was associated with shifts in microbial functional potential, particularly increases in starch‐degrading genes and microbial biomass production potential. Together, our results suggest that warming can restructure microbial communities in ways that strengthen biodiversity‐dependent regulation of soil carbon cycling, with implications for climate‐carbon feedbacks.