Environmental coupling between metal resistance genes and bacterial communities in Beijing urban green-space soils

Urban green spaces are intensively managed ecosystems exposed to chronic, multisource, low-intensity anthropogenic inputs. These inputs may alter soil microbial communities and influence the distribution of metal resistance genes (MRGs). However, MRG distributions and their relationships with environmental conditions and bacterial communities remain unclear under the complex, non-extreme pollution conditions typical of these ecosystems. We investigated Beijing urban green spaces as a representative system using metagenomic sequencing and metagenome-assembled genome (MAG) analysis. We characterized soil MRG composition, its environmental associations, and the distribution of potential hosts. MRG composition differed significantly among ecological conservation (EC), transitional urban (TU), and central urban (CU) zones. These differences were closely associated with soil physicochemical properties and bacterial community structure. Available phosphorus (AP) was significantly associated with variation in both bacterial community structure and MRG composition. MAG-based analysis identified distinct potential-host compositions across the three functional zones. Proteobacteria were more frequently represented among dereplicated MAGs from EC soils, whereas Actinobacteria were more frequent in TU and CU soils. Heavy metal concentrations correlated with MRG composition. However, variation partitioning analysis did not identify an independent contribution from heavy metals after accounting for soil physicochemical properties and bacterial community structure. These findings indicate that urban green-space soil monitoring should incorporate environmental conditions and microbial community characteristics rather than rely solely on total metal concentrations.