Plant Species Diversity Improves Soil Physicochemical Traits and Modulates Soil Microbial Community Structure, with a Pronounced Enhancement of Fungal Diversity in Urban Forests

Urban parks are key to urban ecosystems, where soil microbe-plant-soil interactions sustain ecosystem services. Using high-throughput sequencing and multivariate statistics, this study explored how plant species diversity affects soil microbial community structure, functional diversity, and environmental drivers. Results showed that fungal and bacterial OTUs differed across plant diversity gradients, with Ascomycota (fungi) and Actinobacteriota/Proteobacteria (bacteria) dominant. Soil organic carbon (SOC) was positively correlated with Verrucomicrobia, while Acidobacteriota increased with lower SOC. Fungi were more sensitive to pH than bacteria. Partial Least Squares Path Modeling (PLS-PM) indicated that plant diversity was significantly positively associated with fungal community structure and was indirectly associated with bacterial diversity via soil factors (e.g., SOC, pH), with fungal community variation more explained than bacterial. Higher plant diversity was associated with elevated SOC and a higher relative abundance of putative nutrient-cycling taxa (e.g., <i>Rhizobium</i>), suggesting a potential enhancement of soil nutrient cycling capacity. This study demonstrates that plant diversity shapes microbial communities directly and via soil properties, highlighting synergistic effects. We propose arbor-shrub-herb composite vegetation in urban forest management to optimize microbial habitats and ecological services.