Grazing Management Regimen Shapes Soil Carbon Stocks and Associated Bacterial Community Composition in a Semi-Arid Rangeland

Semi-arid rangelands are highly vulnerable to climate change and overgrazing, yet the functional coupling between soil carbon stabilization and microbial recovery remains largely unquantified. This study was carried out in Northern Mexico (24°0′33″ N, 104°42′28″ W, 1990 m.a.s.l.) and evaluated associations between a grazing management gradient comprising continuous grazing (CG), closed non-selective intensive grazing (GE), and open non-selective intensive grazing (SG) on soil carbon stocks and different labile fractions, bacterial community structures, and functional metabolic pathways in semi-arid soils. The results show that SG showed the highest observed organic and inorganic carbon stocks (SOC and SIC stocks, respectively), along with the labile carbon (LC) fraction. Conversely, GE favors the accumulation of stable, non-labile carbon (NLC). Although alpha diversity remained unaffected, grazing management induced differences in beta diversity. Redundancy and LEfSe analyses revealed a strong coupling between carbon fractions and microbial assembly, characterized by the exclusive enrichment of copiotrophic biomarker families (Burkholderiaceae and Sphingobacteriaceae) under SG. Furthermore, predictive functional profiling (PICRUSt2 and ANCOM) showed that pathways such as tRNA charging and nicotinate degradation were enriched under SG and GE, reflecting potential metabolic capacities and inferred microbial adjustments to heterogeneous, excreta-derived nutrient microenvironments during intermediate recovery states. Ultimately, the findings suggest that targeted rotational grazing may contribute to improved soil carbon stocks and microbial community recovery in semi-arid rangelands.