Abstract:

Aims: Soil bacterial communities serve as pivotal links sustaining plant–soil interaction processes. They play essential roles in regulating soil biogeochemical cycles, facilitating plant community succession, and driving the restoration of soil ecological functions. Currently, the compositional shifts, diversity patterns, functional succession, and underlying influence factors of soil bacterial communities during vegetation restoration in degraded high-altitude forest ecosystems remain poorly understood. 

Methods: We investigated degraded post-fire forest sites of Yulong Snow Mountain in Northwest Yunnan, China, restored with the native shrub Paeonia delavayi for 1-year (1Y), 3-year (3Y), and 6-year (6Y), as well as bare ground formed by post-fire forest undergoing natural succession. Soil physicochemical properties were characterized, and Illumina MiSeq high-throughput sequencing was employed to analyze the composition, diversity, and relationship of functional succession in soil bacterial communities in restoration years. 

Results: (1) With increasing restoration years, soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and soil moisture content (SMC) decreased significantly initially and then increased gradually. Conversely, total potassium (TK) and pH showed an initial increase followed by a decrease. Available phosphorus (AP) and available potassium (AK) in 6-year restoration sites were significantly higher than those in bare ground. (2) Shannon-Wiener, Simpson, and Pielou indices of soil bacterial communities were significantly lower in 3-year and 6-year restoration than in 1-year restoration and bare ground, though Chao1 index showed no significant differences across restoration years. β-diversity showed significant alterations across restoration years. The relative abundances of Pseudomonadota, Acidobacteriota, and Verrucomicrobiota declined markedly with restoration years, whereas Actinomycetota and Gemmatimonadota increased significantly. Chloroflexota peaked in 1-year restoration. The relative abundances of Bradyrhizobium and Mycobacterium (involved in nitrogen cycling) and Gemmatimonas (involved in phosphorus cycling) increased significantly with the restoration years, whereas the relative abundances of Reyranella and Bacillus (biocontrol-associated genera) showed a decreasing trend. (3) RDA analysis indicated that AN, AK, TK, TN, SOC, SMC, and pH significantly shaped bacterial community composition. Structural equation modeling demonstrated that: soil bacterial community diversity exhibited a significant negative correlation with restoration years, while SOC indirectly influenced the community composition by regulating total nutrient content and pH. Conversely, restoration years positively enhanced soil bacterial community composition through its indirect effects on available nutrient. 

Conclusion: A critical shift in the rhizosphere soil of Paeonia delavayi—encompassing physicochemical characteristics, bacterial diversity, abundance of dominant species, and the composition of functional groups—occurred at the 3-year mark of restoration in the degraded post-fire forest. Soil available nutrients continuously improved with restoration years, and the bacterial community composition was significantly enhanced in the later stages of vegetation restoration.

Key words: bacterial community, Paeonia delavayi, restoration years, post-fire forest sites