Fire alters soil bacterial and fungal communities and intensifies seasonal variation in subtropical forest ecosystem

Soil microbes stand as pivotal constituents and perform important ecological functions in forest ecosystems due to their extensive diversity. The increasing frequency of forest fire, coupled with the accelerating global warming, has resulted in changes in environmental conditions and forest structure, consequently influencing soil microbial communities. Despite this, there is a lack of comprehensive understanding regarding the impacts of fire on soil bacterial and fungal communities. Based on a fire experimental study in subtropical forest ecosystem, we investigated the alterations in soil properties and microbial community across two seasons. The results showed that soil bacterial richness remained unchanged by fire in both seasons. In contrast, soil fungal richness decreased in spring but increased in autumn at burnt sites, indicating the amplified seasonal variation induced by fire. In addition, fire had a significant impact on soil microbial community composition. Specifically, it elevated the relative abundance of Actinobacteriota but reduced that of Acidobacteriota and Verrucomicrobiota, which was related to increased temperature, pH, and decreased nitrogen resulting from fire. The relative abundance of Ascomycota increased following fire, whereas the relative abundance of Basidiomycota decreased. These shifts in soil fungal community were mainly related to lower soil carbon:nitrogen ratio. Furthermore, bacterial community was more responsive to environmental changes than fungal community. Overall, our study demonstrates soil microbial diversity and community structure in response to forest fire and the driving factors, advancing our comprehension of soil microbial dynamics in forest ecosystems under environmental perturbations.