Aims The relationships between plant species and soil microorganisms remain indeterminable in different ecosystems worldwide. In karst ecosystems, soil microbial (SM) community structure and their environmental driving factors are poorly explored, and the relationships between plant species and soil microorganisms are unclear. This study aimed to characterize the general patterns of SM community composition and biomass, and to explore the specific tree species and soil physiochemical properties highly related to SM community diversity and biomass in a karst forest.

Methods The effects of tree species on SM community composition and biomass were firstly investigated on the basis of 212 soil samples collected from five dominant tree species (Lithocarpus confinis Huang, Platycarya longipes Wu, Itea yunnanensis Franch., Machilus cavaleriei H. Lev. and Carpinus pubescens Burkill) through phospholipid fatty acid (PLFA) analysis of a karst evergreen and deciduous broad-leaved mixed forest in central Guizhou Province, southwestern China. The relationships between SM community structure and tree species and soil physiochemical properties were statistically analysed.

Important Findings A total of 132 SM-PLFA biomarkers were detected. The average number of SM-PLFA biomarkers and microbial biomass in each soil sample were 65.97 and 11.22 mu g g(-1), respectively. Tree species influenced the number of SM-PLFA biomarkers but not the SM biomass. The number of SM-PLFA biomarkers of C. pubescens was significantly higher than that of other species (P < 0.05); the numbers of SM-PLFA biomarkers amongst other species showed no significant difference. Microbial biomass showed no relationships with the soil physiochemical properties of nutrient-rich surface soils but positively correlated (P < 0.05) with soil organic carbon, nitrogen and phosphorus concentrations in deeper soils. The karst forest in the plateau-surface terrain of central Guizhou Province presented a low fungal-to-bacterial ratio, low microbial biomass storage and high microbial community diversity. Specific tree species affect the SM community diversity in this kind of karst forest.