<p>Urban parks, situated between cities and nature, act as ecological buffers and provide unique niches for soil microbial communities. However, it remains unclear how urbanization affects the functional diversity and evolutionary potential of microbial communities. Here, to address this, we conducted a large-scale field survey across 54 urban park and forest sites in the Pearl River Delta, one of the most rapidly urbanizing regions. Urban parks exhibited higher bacterial and archaeal alpha diversity, biomass, and functional genes related to nutrient cycling compared with forests. These differences were driven by nutrient enrichment and soil pH changes. Microbial genomic analysis revealed a trade-off between short-term ecological functionality and long-term evolvability. Urban parks enhanced immediate functionality but reduced genomic size and evolutionary flexibility, suggesting that urbanization pushes microbial communities toward functional specialization at the expense of adaptive capacity. In contrast, forest soils maintained higher genomic diversity, supporting resilience to environmental changes. These findings highlight the importance of integrating ecological and genomic approaches to predict ecosystem service sustainability in urbanizing areas.</p>