Impact of urbanization on soil microbial diversity and composition in the megacity of Shanghai

Urbanization alters the physicochemical environment on an unprecedented scale and strongly affects biodiversity. How urbanization affects the biodiversity of soil microbial communities, especially in large cities, however, is poorly known. We investigated soil microbial communities from 258 sites covering a variety of environmental gradients in the megacity of Shanghai, China, to determine the impact of urbanization on soil microbial biodiversity. Using the distance to city centre, urbanized land cover, and road density as three proxies to characterize the levels of urbanization, we revealed that increased urbanization was associated with slightly homogenized communities of prokaryotes, total fungi, and arbuscular mycorrhizal fungi but not ectomycorrhizal fungi. The richness of soil prokaryotes and total fungi was weakly but positively related to urbanization as well. For the abundance of microbial phylotypes along urban gradients, we observed synchronous increases and decreases of many phylotypes at relatively high and low urbanization levels, respectively. Further, urbanization explained an independent part of microbial variances in richness and community composition, although the contribution of soil properties in explaining the variances was generally larger than that of urbanization. Together, this work provides evidence for the influences of urbanization on the biodiversity of soil microbes and highlights the importance of considering taxa and the level of urbanization to assess the impacts of urbanization on biodiversity.