Abstract: As a vital component of the boreal forest, Larix gmelinii forests face severe threats from frequent wildfires. Soil microorganisms play a key role in forest ecosystems by participating in biogeochemical cycles and maintaining a close association with plants. To elucidate the effects of wildfires on soil microorganisms in L. gmelinii forests, we collected soil samples from burned and unburned forests in Northeast China during both summer and winter for amplicon sequencing. The results showed that wildfires significantly increased soil microbial diversity and markedly altered soil microbial community structure. Soil pH was the most important factor influencing microbial community diversity and composition. Compared with unburned networks, the burned networks were much less complex and stable, with a significantly higher proportion of fungus-related correlations. Additionally, the relative importance of deterministic processes in forming both bacterial and fungal communities was lower in the burned forest than in the unburned forest within the same season. Our study illustrated the effects of wildfire on soil microorganisms from the perspectives of community structure, networks and assembly process, and demonstrated the crucial role of soil fungi in post-fire restoration of ecological functions.

Key words: wildfire disturbance, soil microorganisms, Larix gmelinii forest, co-occurrence network, community assembly