Grazing disturbance reduces soil organic carbon sequestration and stability in desert steppe

While grazing effects on soil organic carbon (SOC) stocks are documented, how stocking rates repartition carbon between labile and stable fractions in desert steppes remains unknown. Previous studies have focused predominantly on individual carbon pool stocks rather than on inter-component equilibrium. Here, we evaluated the results of a twenty-year controlled grazing experiment, systematically analyzing how prolonged stocking pressure alters the proportional stability of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) by disrupting the formation of POC and MAOC from plant and microbial precursors. We found that, despite maintaining stable proportions relative to total SOC, POC and MAOC sub-pools exhibited parallel declines under overgrazing. This demonstrates that SOC destabilization arises from systemic changes to carbon repartitioning rather than from isolated pool depletion. Grazing-induced shifts in plant community composition and soil structural features impaired microbial functionality and enzymatic processes, limiting the transformation of organic substrates into more stable forms of soil carbon. These findings advance desert steppe management by highlighting the importance of prioritizing component ratio stability over conventional stock-based metrics and offers actionable strategies to balance carbon sequestration.