Fire Severity Alters Soil Microbial Diversity and Community Stability in a Subtropical Forest Ecosystem

Wildfire is a critical ecological disturbance that affect soil chemical properties and microbial communities, with varying fire severities exerting distinct and decisive influences on the capacity for post-fire recovery. Here, we collected field data from Pinus yunnanensis forests in Yunnan Province, southwestern China, to examine the short-term impacts of low-severity fires, high-severity fires, and unfired controls on the composition, diversity, function, and co-occurrence networks of soil bacterial and fungal communities, and to identify key soil properties driving microbial community changes following fire disturbances. Our findings found that fire significantly altered the composition of both bacterial and fungal communities. Additionally, soil microbial diversity was significantly lower in high-severity fire sites compared to unfired controls. Moreover, low-severity fires increased the functional taxa associated with chemoheterotrophic and aerobic chemoheterotrophic bacteria, whereas the ectomycorrhizal fungi was significantly reduced in fired plots. Network analysis indicated that the complexity and connectivity of microbial networks gradually decreased with increasing fire severity. Under high-severity fire, bacterial networks exhibited increased competitive interactions, while fungal networks showed enhanced co-occurrence. Bacterial and fungal richness declined with increasing TOC and SOM, while Shannon diversity was positively associated with pH and AP. These findings underscore the differential impacts of fire severity on bacteria and fungi, which will provide valuable insights for improving environmental management and guiding post-fire recovery in fire-prone forest ecosystems.