Abstract
Soil microbes are crucial for biogeochemical cycles and their functional potential is greatly affected by ecosystem management. Yet, how does grass vegetation affect the composition of soil microbial communities and the abundance of key nutrient-cycling functional genes? In this study, based on an experimental plot built for 7 years, the long - term influence of two grass vegetation types (Carex breviculmis and Festuca arundinacea Schreb) on soil microbial community structure and C, N, P, and S cycles were explored by metagenomics. The results showed that both plants significantly increased the diversity and richness of soil bacteria and fungi, and the abundance of Pseudomonadota and Ascomycota in Carex breviculmis increased significantly, while those of Actinomycetota and Mucoromycota decreased. Microbial network analysis shows that Carex breviculmis forms a highly modular, low - complexity microbial interaction network, indicating specialized and stable microbial community functions. Conversely, Festuca arundinacea Schreb has a more complex and less modular network, suggesting enhanced microbial interactions. Carex breviculmis significantly increased the abundance of genes related to carbon fixation (fumA/B, pps, ppc) and phosphorus mineralization (phoR/P/B, phnF/P), and also enhanced soil denitrification potential. In contrast, Festuca arundinacea Schreb showed a enrichment of soil nitrogen fixation genes (nifh). Additionally, growing Carex breviculmis and Festuca arundinacea Schreb induced the growth of sulfur - oxidizing bacteria (e.g., Thiobacillus), enriching the abundance of sulfur - metabolism - related genes (apr, sox). Genes related to microbial C, N, P, and S cycles are positively correlated with soil pH, available P, and alkali-hydrolyzed nitrogen. Overall, this study reveals how different grass vegetation types regulate microbial community structure and functional gene abundance to drive nutrient cycling differentiation in grassland ecosystems, thereby providing a theoretical basis for optimizing grass vegetation configuration in managed and restored grasslands to enhance soil ecological functions.