Land-use change is a major long-term driver shaping the evolution of subtropical ecosystems, and its cumulative effects profoundly alter soil environments and microbial processes. In this study, we employed a 70-year land-use chronosequence in Qingpu District, Shanghai—spanning natural woodland, paddy fields, orchards, and urban green spaces—to systematically evaluate how long-term land-use transitions reshape soil functions, microbial communities, and co-occurrence networks, as well as their cascading regulatory mechanisms. Our results show that land-use transitions markedly restructured soil functions, particularly inducing strong functional divergence in soil carbon and nitrogen cycling. Anthropogenic management led to a decoupling pattern of “increased total nutrient pools but reduced nutrient lability,” indicating a structural decline in soil nutrient supply capacity and a reconfiguration of transformation pathways. Microbial communities exhibited clear shifts in ecological strategies: natural woodland was dominated by oligotrophic taxa, whereas managed systems favored copiotrophic or stress-tolerant groups, accompanied by reduced spatial heterogeneity—a pattern reflecting environmental filtering and biotic homogenization. Microbial interaction networks also underwent structural reorganization: orchard and urban-green-space networks became more tightly connected but less modular, while the paddy network was simplified under persistent anaerobic stress. Structural equation modeling further revealed a cascading pathway of “functions → taxa → networks”: land-use change regulates soil pH and dissolved organic nitrogen, which influence microbial metabolic activity and community heterogeneity; these two factors jointly determine network stability—heterogeneous communities enhance robustness, whereas elevated metabolic activity weakens stability by intensifying resource competition. This study provides a multidimensional understanding of soil ecosystem responses to long-term anthropogenic disturbance and offers critical scientific insights for sustainable land management and ecological restoration in subtropical regions.