Forest ecosystem changes under monodominant plant expansion represent one of the most pressing ecological challenges globally, as they are associated with significant shifts in biogeochemical cycles and ecosystem functioning. Despite extensive research, the fundamental knowledge gap regarding microbial taxonomic diversity and its functional linkage persists. Here, we investigated how Moso bamboo ( Phyllostachys edulis) expansion reconfigures soil microbiome functional potential across a forest transition gradient (from non-expanded forest to mixed to bamboo-dominated forests) in the Jinggangshan National Nature Reserve, China. Through shotgun metagenomic analysis, we found that bamboo forests exhibited significant enrichment in diverse metabolic pathways spanning carbon ( glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules), nitrogen ( nitrification, denitrification, dissimilatory nitrate reduction, organic nitrogen processing), and phosphorus ( organic phosphoester hydrolysis, transporters, pentose phosphate pathway, phosphotransferase systems, phosphonate and phosphinate metabolism and pyruvate metabolism) cycling genes compared to non-expanded forests, creating a specialized metabolic infrastructure supporting bamboo’s acquisitive ecological strategy. Notably, co-occurrence network analysis revealed distinct patterns in bamboo-dominated soils, with functional gene networks exhibiting higher connectivity, more dense clustering, and a predominance of positive correlations compared to non-expanded forests. Soil calcium concentration showed the strongest statistical association with functional gene composition, explaining 20-28% of the observed variability in functional gene profiles. Our findings reveal specific functional gene signatures and network properties potentially supporting bamboo’s acquisitive ecological strategy and rapid expansion, suggesting that distinctive plant-soil-microbe functional relationships may play an important role in the success of monodominant vegetation in subtropical forest ecosystems.