Land use change directly influences soil microbial communities by altering vegetation cover. However, how soil
microbial community structure responds spatially to plant distribution within a land use type following afforestation remains unclear. Here, we investigated the spatial variations in soil microbial biomass [e.g., bacteria (B), fungi (F), gram-positive bacteria (G+), and gram-negative bacteria (G？)] and community composition (the F:B ratio and G+:G- ratio) in woodland, shrubland and adjacent open areas (i.e., control) in the Danjiangkou
Reservoir of central China, using geostatistical methods and phospholipid fatty acid (PLFA) analysis. We also explored the underlying mechanisms of whether or not and how environmental drivers, including biotic factors (e.g., tree distribution, present litter and root biomass) and abiotic factors [e.g., soil organic carbon (SOC) and total nitrogen (TN), soil pH, and soil moisture], regulated the spatial variations in these microbial properties using partial Mantel tests. Afforestation increased the PLFA content and the G+:G- ratio but reduced the F:B ratio compared to that of the open area. Spatial analysis revealed that spatial variations in microbial communities were governed by local environmental drivers affected by tree distribution. Generally, SOC was a critical control on microbial biomass and community composition in all land use types, but the major drivers varied with land use type. Soil pH, SOC and TN affected almost all types of microbial PLFAs in shrubland, whereas litter biomass, SOC and TN were selectively correlated with specific groups of PLFAs (mainly from bacteria) in woodland. Soil pH affected the F:B ratio rather than the G+:G- ratio in both woodland and shrubland, while root biomass, SOC and TN were proved to be determinants of the F:B ratio and G+:G- ratio in shrubland. Other than SOC, the soil pH and N level were the primary controls on spatial variations in microbial biomass following afforestation. Overall, our results revealed that tree distribution-induced shifts in local environments controlled the spatial variations in soil microbial community structure within one land use type, highlighting that the role of spatial heterogeneity in microbial communities has important implications for land management.