Soil properties, rather than urbanization time, drive shifts in soil bacterial communities in a subtropical city of China

Urbanization strongly alters soil environments and may reshape soil bacterial communities (SBC), yet their responses across long-term urbanization stages remain unclear. Using Shenzhen, China, a subtropical city that urbanized within 40 years, we investigated SBC diversity, composition, and co-occurrence network stability across different land-use types and urbanization stages. Soil bacterial α-diversity showed no significant differences between natural forests and urban ecosystems. However, bacterial composition shifted markedly during urbanization, with dominant taxa changing from Acidobacteriota and Verrucomicrobiota in forests to Actinobacteriota , Chloroflexi , and Firmicutes in urban soils. SBC composition remained strongly associated with soil physicochemical properties rather than converging across urbanization stages, indicating dominant environmental filtering effects. Network analyses further revealed non-linear changes in resistance and resilience stability along the urbanization chronosequence, associated with shifts in network topology and soil properties. Together, our results show that urbanization does not drive a uniform trajectory of SBC assembly; instead, soil environmental conditions under different land-use types primarily shape bacterial composition and potential stability type. IMPORTANCE Urbanization is rapidly transforming soil ecosystems worldwide, but its impacts on soil bacterial communities remain poorly understood. We show that urbanization in a subtropical city caused major shifts in dominant bacterial taxa. Urban soils were characterized by a transition from oligotrophic to copiotrophic taxa, accompanied by contrasting changes in network-inferred resistance and resilience stability. These patterns were primarily driven by changes in soil properties associated with land-use change, highlighting the importance of environmental filtering in shaping urban soil microbiomes. Our findings improve understanding of how urbanization restructures underground ecosystems and their potential stability under long-term environmental change.