Abstract:

Aims: This study aimed to evaluate the effects of fire disturbance on soil microbial communities in Pinus densata forests and to characterize their recovery trajectories across different post-fire recovery stages. 

Methods: Soil microbial communities in unburned plots and fire-affected plots at 5 and 14 years post-fire in Pinus densata forests were investigated using Illumina MiSeq high-throughput sequencing combined with bioinformatic analyses. 

Results: (1) By 14 years post-fire, several soil nutrient indices had recovered to, and in some cases exceeded, the levels of the unburned plots. In the 0–5 cm layer, soil organic matter, total nitrogen, total phosphorus, nitrate nitrogen, and pH increased significantly (P < 0.05), while in the 5–10 cm layer, significant increases were observed only in soil organic matter, total phosphorus, and nitrate nitrogen (P < 0.05). (2) In the 0–5 cm soil layer, the Shannon index of bacterial communities at 5 and 14 years post-fire was significantly higher than that in the unburned plots (P < 0.05), whereas no significant differences were observed among the different post-fire recovery stages for bacteria in the 5–10 cm layer or for fungi in either soil layer (P > 0.05). (3) In both 0–5 cm and 5–10 cm soil layers, bacterial communities were dominated by Actinobacteriota, Proteobacteria, and Acidobacteriota, while fungal communities were primarily composed of Ascomycota and Basidiomycota. By 14 years post-fire bacterial absolute abundance exceeded that in unburned plots, whereas fungal absolute abundance remained lower. (4) Symbiotrophic and saprotrophic fungi exhibited differentiated recovery trends across soil layers, whereas the relative abundance of multitrophic fungi showed an initial increase followed by a decrease. (5) Post-fire recovery time significantly affected the community structures of both soil bacteria and fungi in the 0–5 cm and 5–10 cm layers (P < 0.05), with pH, organic matter, and nitrogen and phosphorus availability closely associated with microbial community differentiation. 

Conclusion: Long-term recovery following fire disturbance led to significant changes in soil organic matter, total nitrogen, total phosphorus, pH, and nitrate nitrogen, which indirectly influenced the Shannon index of bacterial communities in the 0–5 cm layer and the overall microbial community structure in both soil layers. Multitrophic fungi, capable of utilizing multiple carbon sources simultaneously, gained a competitive advantage for resources after fire disturbance, resulting in a relative increase in abundance in the short term. As recovery time increases, the ecosystem gradually stabilizes, allowing monotrophic fungi to reoccupy their ecological niches. Because environmental factors were highly synchronized between the two soil layers, microbial community structure did not differ significantly along the vertical (depth) gradient within any given recovery stage.

Key words: fire disturbance, absolute abundance, soil recovery, pinus densata, recovery stage