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Both microbes and plants contribute to soil organic carbon (SOC) formation and retention, but their roles in controlling SOC dynamics in forest soils under Moso bamboo (Phyllostachys edulis) expansion remain unclear. Here, amino sugars and lignin monomers were measured to represent microbial necromass and plant‐derived components, respectively. The observed decline in both amino sugars and lignin monomers during Moso bamboo expansion indicates a reduction in microbial necromass and recalcitrant plant contributions to SOC composition. This could be attributed to a limitation of microbial substrates and proliferation caused by the reduced litter inputs resulting from the expansion. The proportion of microbial necromass contributing to the SOC pool increased, but that of lignin monomers decreased, as SOC content decreased with Moso bamboo expansion. This suggests that the decrease of SOC during bamboo expansion was mainly due to the reduction of lignin, while the increased contribution of microbial‐derived carbon to SOC may serve to improve SOC stability. Our study sheds light on the altered SOC source inputs resulting from Moso bamboo expansion and emphasizes the need for sustainable forestry management practices that differentiate between microbial‐ and plant‐derived carbon pools. [ABSTRACT FROM AUTHOR]

• Bamboo invasion consistently increased soil pH and organic C content across three sites. • Bamboo invasion consistently decreased fungal ITS gene abundances across the sites. • Bamboo invasion improved the closeness of soil bacterial but not fungal communities. • Total soil enzyme activities positively correlated with the abundances of fungi rather than bacteria. Moso bamboo (Phyllostachys edulis) invasions into adjacent forests have been reported to threaten aboveground biodiversity and alter belowground soil processes. However, the impacts of bamboo invasion on soil microbial community composition, co-occurrence network and enzyme activity remain largely unknown. We presented a cross site field investigation on soil bacterial and fungal communities and enzyme activities in three forests (an original broadleaf forest, a mixed bamboo-broadleaf forest and a pure bamboo forest) at three sites in South China. Our results showed that bamboo invasion consistently increased soil pH (by 6.72% − 17.56%) and soil organic carbon concentrations (by 11.75% − 40.63%) across the three sites. Bamboo invasion consistently decreased fungal ITS gene abundances across the sites, but had little effect on bacterial 16S rRNA gene abundances and diversity indices. The community composition of both bacteria and fungi and their functional guilds differed among the three sites and were significantly (P < 0.05) affected by bamboo invasion. Bamboo invasion significantly decreased the relative abundances of ectomycorrhizal but increased those of soil saprotrophs. The complexity of co-occurrence network of bacterial communities was increased whereas that of fungal communities was decreased due to bamboo invasion. The activities of soil enzymes involved in C, N and P cycling were also altered by bamboo invasion, and they were significantly positively correlated with the abundances of fungal ITS gene and ectomycorrhizal rather than those of bacteria and predicted metabolic function. This study suggested that bamboo invasions into adjacent broadleaf forests had contrasting effects on soil bacterial and fungal communities by shifting microhabitats towards a condition that is unfavorable for some fungal functional guilds, which were tightly associated with soil functioning. These results highlight the need for sustainable forestry management against bamboo invasion to maintain fungal diversity and network complexity. [ABSTRACT FROM AUTHOR]

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, NO 3 −-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. • The effects of intensive forest management on soil microbial community were investigated. • Prolonged intensive management decreased bacterial diversity indices and metabolic function. • Changes in enzyme activity were tightly linked to bacterial community and function. • The observed decreases in microbial diversity may have direct consequences for soil functioning. [ABSTRACT FROM AUTHOR]