Structure and function of the topsoil microbiome in Chinese terrestrial ecosystems.

While soil microorganisms underpin terrestrial ecosystem functioning, how their functional potential adapts across environmental gradients remains poorly understood, particularly for ubiquitous taxa. Employing a comprehensive metagenomic approach across China's six major terrestrial ecosystems (41 topsoil samples, 0-20 cm depth), we reveal a counterintuitive pattern: oligotrophic environments (deserts, karst) harbor microbiomes with significantly greater metabolic pathway diversity (KEGG) compared to resource-rich ecosystems. We provide a systematic catalog of key functional genes governing biogeochemical cycles in these soils, identifying: 6 core CAZyme genes essential for soil organic carbon (SOC) decomposition and biosynthesis; 62 nitrogen (N)-cycling genes (KOs) across seven critical enzymatic clusters; 15 sulfur (S)-cycling genes (KOs) within three key enzymatic clusters. These functional gene abundances exhibit distinct, geography-driven clustering patterns, strongly correlated with eight environmental drivers (latitude, NDVI, pH, EC, SOC, TN, C:N ratio, and MAP). This work provides a predictive framework and actionable genetic targets (e.g., specific CAZyme, N/S cycling genes) for potentially manipulating soil microbiomes to enhance ecosystem resilience and biogeochemical functions under stress.