Soil microbial community changes in response to the environmental gradients of urbanization in Guangzhou City

Soil microbes play important roles in many terrestrial ecological processes. Rapid urbanization causes drastic changes in land use and land cover, thus forming a heterogeneous environmental gradient and directly or indirectly affecting the composition and function of soil microbial communities. To investigate the effects of rapid urbanization on soil microbial community composition and function, we analyzed soil microbial communities by quantifying phospholipid fatty acids among the land cover categories (rural forests, urban low-impacted forest fragments, urban high-impacted forest fragments, and urban parks) in Guangzhou. We found that soil microbial communities differed across this urbanization gradients. Specifically, compared to the rural forest ecosystems, the biomass of Actinobacteria and gram-positive bacteria in urban high-impacted forest fragments ecosystems were 53.8% and 31.23% greater, respectively, while the biomass of Actinobacteria and gram-positive bacteria in urban park ecosystems were 67.8% and 37.45% greater respectively. Microbial communities of rural forests and urban low-impacted forest fragments, characterized by lower urbanization intensity, were dominated by the microbial groups, 19:0cy, i16:0, i15:0, 15:0, 18:0 (bacterial biomarkers), 18:2ω6c (fungal biomarkers), and 10Me17:0 (Actinobacterial biomarkers), whereas the urban park and urban high-impacted forest fragments, characterized by higher urbanization intensity were dominated by the microbial groups, 18:1ω5c, 18:1ω7c, cy17:0, i17;0, a17:0, 16:1ω9c, a15:0, i14:0 (bacterial biomarkers), 16:1ω5c (fungal biomarkers), and 10Me16:0 (Actinobacterial biomarkers). Fungal biomass was positively correlated with soil pH and the metal comprehensive index, whereas bacteria were only positively correlated with soil organic matter. Soil pH, organic matter, total nitrogen content and the heavy metal comprehensive index were all positively correlated with total soil microbial biomass and Actinobacterial biomass. These results suggest that rapid urbanization caused land use and land cover changes that significantly affect soil microbial community composition, and urbanization impacts soil properties which then affect soil microbes.