Diversity and function of soil bacterial communities in response to long-term intensive management in a subtropical bamboo forest

Intensive forest management practices, such as fertilization, understory removal and deep tilling, play an important role in improving plant growth in forests through altering nutrient availability and soil structure. However, how such management affects soil microbial community diversity and functions related to nutrient cycling remains largely unknown. In this study, we investigated the responses of soil bacterial community composition and enzyme activities involved in C, N and P cycling to long-term intensive management, and identified the critical determinants that regulated them across a chronosequence of Moso bamboo forests (0, 10, 15, 20 and 25 years of intensive management) in subtropical China. Our results demonstrated that intensive management decreased soil pH and aggregation and increased mineral nutrient contents. Illumina MiSeq sequencing showed that significant (P < 0.05) shifts of the soil bacterial community composition occurred after 15 years of management. Diversity indices (phylogenetic diversity, OTU richness and Chao1) generally decreased after 15 years of management. Soil pH, NO3−-N, and available P and K contents were key factors shaping the bacterial community composition. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) predicted lower functional diversity of soil bacterial microbiomes as related to the cycling of amino acids and carbohydrates after 15 and 20 years. The activities of β-glucosidase and phosphatase decreased markedly after 15 years of intensive management, but rebounded after 25 years. Structural equation modeling provided evidence that the response of soil enzyme activities to forest management was mediated by changes in bacterial composition and diversity. Our study suggests that intensive forest management decreases microbial diversity indices and changed community composition, which could have direct consequences for soil functioning.