Land use, soil fertility, and heavy-metal concentrations in relation to soil microbial communities in urban green spaces

Urbanization introduces heavy-metal contamination while reshaping soil habitats through greenspace management, but their relative roles in structuring soil microbial communities remain unclear. We analyzed soils from industrial areas, urban parks and natural mountainous sites in Xiamen, China, using 16S rRNA gene sequencing, PICRUSt2 functional prediction, generalized linear models, distance-based redundancy analysis and piecewise structural equation modeling. Industry and park soils had approximately 42%—45% higher bacterial richness than mountainous soils (both p < 0.001), and richness reached its maximum when Cd < 0.25 mg.kg −1 and total phosphorus (TP) > 6 mg·kg −1 . Land use was the main driver of richness, while soil fertility (mainly TP and pH) was the main driver of community composition, independently explaining 15.85% of compositional variance versus 2.97% for heavy metals; under the moderate, sub-toxic contamination levels examined here, all measured metal concentrations remained below national soil-quality screening values, and heavy metals played only a secondary role in shaping community composition. Mountainous, park and industry soils showed predicted enrichment of biosynthesis, energy metabolism and stress-response pathways, respectively. Our research indicates that, under comparable background contamination levels, systematic greenspace management prioritizing soil fertility can help maintain microbial diversity without large-scale remediation.