Direct effects of fire severity on soil microbial diversity and network assembly in a transitional climate forest

Abstract Forest fires are key ecological disturbances that influence vegetation dynamics and soil microbial processes central to carbon and nutrient cycling. While fire frequency and severity are increasing globally, the microbial mechanisms underlying ecosystem recovery remain inadequately understood. We used high-throughput amplicon sequencing to evaluate short-term effects of low- and high-severity fires on soil microbial diversity and co-occurrence networks following fire disturbance in a temperate forest. Fire severity had no significant impact on microbial α-diversity, but significantly altered β-diversity. Mantel tests indicated that soil pH and belowground biomass were the primary environmental drivers of bacterial and fungal community turnover under different fire severities. Further, network analyses revealed distinct microbial responses to fire severity: low-severity fire primarily restructured bacterial associations, whereas high-severity fire disrupted both bacterial and fungal networks. These findings suggest that microbial community structure and interactions are differentially sensitive to fire severity, with implications for soil functional resilience and ecosystem restoration strategies in fire-affected forests.