Abstract: Aims In boreal forest ecosystems, forest fires and soil microorganisms, along with their interactions, play a crucial role in shaping the soil environment. The rhizosphere soil microbial community, being one of the most sensitive bioindicators to environmental changes, provides critical insights into the stability of soil ecosystems. Understanding the structural changes in both rhizosphere and bulk soil microbial communities is essential for a comprehensive assessment of soil environmental stability in boreal forests. Methods This study focused on the rhizosphere soil of Larix gmelinii, a dominant tree species in northern China's forests. Fungal and bacterial communities were analyzed using ITS and 16S rRNA high-throughput sequencing technologies to investigate the effects of forest fires on the dynamics of soil microbial communities. Important findings (1) Forest fires significantly reduced soil organic carbon content (decreased by 40.1% in rhizosphere soil and 15.7% in bulk soil), total nitrogen content (decreased by 51.3% in rhizosphere soil and 38.9% in bulk soil), as well as β -1,4-glucosidase activity (decreased by 83.4% in rhizosphere soil and 72.7% in bulk soil) and β -1,4-N-acetylglucosamine glucosidase activity (decreased by 54.6% in rhizosphere soil and 13.4% in bulk soil), while dissolved inorganic nitrogen content increased significantly after the fire (increased by 21.1% in rhizosphere soil and 431.6% in bulk soil). (2) After fire, the Shannon Wiener index of fungi in rhizosphere and bulk soils decreased significantly (decreased by 12.2% in rhizosphere soil and 13.7% in bulk soil), while the Shannon Wiener index of bacteria increased significantly (increased by 8.8% in rhizosphere soil and 10.2% in bulk soil). β-diversity analysis further revealed significant differences in fungal and bacterial community structures between rhizosphere and bulk soils. (3) Redundancy analysis shows that soil organic carbon, total nitrogen, dissolved organic carbon, dissolved inorganic nitrogen content, β -1,4-glucosidase activity, and β -1,4-N-acetylglucosamine activity are the main factors affecting the fungal and bacterial community structure in rhizosphere and bulk soils after fire. Structural equation modeling further elucidated the direct and indirect effects of forest fires on soil properties, enzyme activities, and microbial community structures. This study is helpful in understanding the changes of soil microbial community structure in the Great Xing’an forest area after fires, which is of great significance for post fire ecological restoration and the adoption of corresponding protection and management measures.

Key words: forest fires, soil microbial community, rhizosphere soil, Larix gmelinii, microbial diversity