Objective  This paper aims to analyze the variation of soil microbial community structure characteristics of larch plantation at different plantation ages, clarify the response mechanism of soil microbial community structure to the changes of plantation age and its key influencing factors, provide theoretical basis for sustainable management of the plantation and feedback effect of soil microbial community to environmental changes.

  Method  Based on the characteristics of soil microbial community structure, soil physical and chemical properties and understory vegetation characteristics database, this study explored the regulation mechanism of soil physical and chemical properties and understory vegetation characteristics on the formation of soil microbial communities by redundancy analysis.

  Result  The change of plantation age had a significant impact on soil physical and chemical properties and microbial community structure, such as soil temperature, water content, pH, total carbon, total nitrogen, total phosphorus, ammonium nitrogen and nitrate nitrogen content increased significantly with the increase of plantation age, but the soil available phosphorus content showed the opposite trend (P < 0.05). Meanwhile, the growth of the plantation age also significantly increased the abundance of gram-positive bacteria, gram-negative bacteria, fungi and actinomycetes in the soil, while the ratio of fungi: bacteria and gram-positive bacteria: gram-negative bacteria showed a downward trend. The diversity of understory shrubs and herb layers also showed a trend of increasing with the increase of forest age, and the differences between different forest ages did not reach a significant level. The results of redundant analysis showed that the soil physical and chemical properties and the understory vegetation diversity index explained 86.1% of the total variation of the soil microbial community, while the soil water content, soil temperature, available phosphorus, nitrate nitrogen content, and the richness index of shrub and herb layer explained 22.7%, 18.4%, 11.8%, 10.6%, 7.9% and 5.6% of the variation of microbial community structure, respectively.

  Conclusion  The structural characteristics of soil microbial community, soil physical and chemical properties, and understory plant diversity (ie shrub layer and herb layer) are all affected by changes of plantation age. Notably, soil temperature, water content, available phosphorus, nitrate nitrogen, and understory vegetation diversity are key factors to drive the changes of soil microbial community structure in different plantation ages.