Aims This study aimed to determine the influence of tree species on soil microbial community structure. Methods We conducted a litter and root manipulation and a short-term nitrogen (N) addition experiment in 19-yearold broadleaf Mytilaria laosensis (Hamamelidaceae) and coniferous Chinese fir (Cunninghamia lanceolata) plantations in subtropical China. Phospholipid fatty acid (PLFA) analysis was used to examine treatment effects on soil microbial community structure. Redundancy analysis (RDA) was performed to determine the relationships between individual PLFAs and soil properties (soil pH, carbon (C) and N concentration and C:N ratio). ResultsSoil C:N ratio was significantly greater in M. laosensis (17.9) than in C. lanceolata (16.2). Soil C:N ratio was the key factor affecting the soil microbial community regardless of tree species and the litter, root and N treatments at our study site. The fungal biomarkers, 18:1ω9 and 18:2ω6,9 were significantly and positively related to soil C:N ratio and the abundance of bacterial lipid biomarkers was negatively related to soil C:N ratio. N addition for 8 months did not change the biomass and structure of the microbial community in M. laosensis and C. lanceolata soils. Soil nutrient availability before N addition was an important factor in determining the effect of N fertilization on soil microbial biomass and activity. PLFA analysis showed that root exclusion significantly decreased the abundance of the fungal biomarkers and increased the abundance of the Gram-positive bacteria. Rootless plots had a relatively lower Gram-positive to Gram-negative bacteria ratio and a higher fungi to bacteria ratio compared to the plots with roots under both M. laosensis and C. lanceolata. The response of arbuscular mycorrhizal fungi (16:1ω5) to root exclusion was species-specific. Conclusions These observations suggest that soil C:N ratio was an important factor in influencing soil microbial community structure. Further studies are required to confirm the long-term effect of tree species on soil microbial community structure.

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Aim Although global patterns are emerging for the soil total microbial biomass pool, our understanding of the distribution of the finer groups, especially bacterial and fungal biomass, remains limited. Moreover, we lack mechanistic insights into the global variation of soil microbial biomass. Location Global terrestrial ecosystems. Time period 1990–2019. Major taxa studied Bacteria and fungi. Methods By conducting a global synthesis of 4,472 observations from 577 sites published in 404 studies, we examined the global patterns and drivers of the soil total microbial biomass, bacterial and fungal biomass and fungi‐to‐bacteria ratio. Results We found that soil total microbial, bacterial and fungal biomass peaked concurrently in tundras, with lower values in deserts, and that intensification of land use reduced soil total microbial, bacterial and fungal biomass and the fungi‐to‐bacteria biomass ratio. Soil organic carbon was the most important driver for global distribution patterns of both bacterial and fungal biomass. Our structural equation models indicated that soil bacterial and fungal biomass increased with water availability through its positive effect on soil organic carbon on a global scale. In contrast, soil total, bacterial and fungal biomass decreased with mean annual temperature and intensification of land use via their negative effects on soil organic carbon. Main conclusions Our results suggest that decreasing water availability and land‐use intensification could reduce soil microbial biomass and the relative abundance of soil fungi to bacteria, impairing their functions and the services they provide.

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