Changes in the Soil Microbial Community Structure and Driving Factors during Post-Fire Recovery of the Larix gmelinii Rupr. Forest in Northern China

Compared to soil bacterial communities, fungal communities experienced the most significant impact from fire and required a longer recovery period [41]. This study demonstrated that fire significantly reduced the richness (as indicated by the Ace index and Chao indices) and diversity (as measured by the Shannon index) of soil fungal communities. Remarkably, even 11 years after the fire, these communities did not fully recover to their pre-fire levels (Table 3). The utilization of PCoA and NMDS (Figure 2b,d) elucidated notable disparities in the soil fungal community structure between the 1a and 6a fire-affected sites compared to the CK, whereas the fungal community structure of the 1a fire-affected site closely resembled that of the CK site. The RDA results indicated the pivotal role of TN (explaining 47.47%, p = 0.01) in elucidating a substantial proportion of the variation in fungal community diversity across distinct post-fire recovery years (Figure 4b). Nitrogen played a fundamental role in the growth and metabolic activity of soil fungi and contributed to several critical biochemical processes. After the fire, the level of TN in the soil was reduced, requiring 11 years to recover to pre-fire levels (Table 2). TN exhibited a positive correlation with the fungal community at the 11a fire-affected site (Figure 4b). Ascomycota and Basidiomycota consistently accounted for higher relative abundance across various post-fire recovery years within the burned areas. Although the relative abundance of these phyla may vary with different recovery periods, their dominance remains unchanged. Basidiomycota and Ascomycota persisted as the principal fungal phyla in areas subjected to varying fire intensities, which was consistent with previous studies on soil fungal community composition in Larix gmelinii forests within the Great Xing’an Mountains [42]. Basidiomycota frequently establish mycorrhizal associations with plant roots, enhancing the nutrient uptake and the plant growth in the soil. These fungi exhibit low resistance to environmental disturbances, as fire not only removes aboveground vegetation but also affects belowground plant roots, reducing the relative abundance of Basidiomycota following a fire event [43]. Conversely, Ascomycota, with the capacity to produce extracellular enzymes, excelled at decomposing recalcitrant substances, such as lignin and cellulose. They were notably sensitive to plant residues and debris [44]. After the fire, there was a pronounced increase in dead branches, fallen leaves, and ash from vegetation on the ground surface, increasing the relative abundance of Ascomycota. However, with the increase in recovery years, the dominance of Ascomycota gradually decreased, being replaced by Basidiomycota, which was consistent with the findings of Meng [35].