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Grasslands store 10 –30% of the world's soil organic carbon (SOC) and have the potential to partially mitigate rising atmospheric CO 2 concentrations. Large ungulate grazing plays a crucial role in regulating SOC storage in grassland ecosystems. However, a more detailed mechanistic understanding of how grazing influences SOC dynamics is still needed. We investigated soil C formation among different C pools, including particulate organic carbon (POC) and mineral-associated soil organic carbon (MAOC) in a multiyear field experiment by quantifying litter-derived C inputs, in response to mowing, trampling, and dung and urine return (and combinations), treatments. We found that mowing significantly enhanced litter-derived SOC and POC formation. Trampling increased SOC, POC and MAOC pool, possibly by enhancing mixing of litter and soil, and increasing C accessibility for soil microorganisms. Our results elucidated the specific mechanisms of large ungulate grazing by quantifying the C inputs and formation processes. Accurately quantifying the contribution of plant C input to SOC pool under various management practices in grasslands is the next critical step toward improving predictions of SOC dynamics.