Dynamics and driving mechanisms of soil organic carbon sequestration in grasslands after grazing exclusion: A review.

Abstract

Grazing exclusion is the most effective measure to restore the structure and function of degraded grasslands, and plays a crucial role in increasing ecosystem carbon (C) sequestration capacity. The dynamics and dri-ving mechanisms of soil organic carbon (SOC) after grazing exclusion have attracted great concerns, especially in the context of global change. By reviewing the current research on the SOC sequestration dynamics and its driving mechanisms after grazing exclusion, we aimed to clarify the SOC sequestration dynamics, explore the influencing mechanisms of plant C input and microbial community on SOC, analyze the driving mechanisms of photosynthetic C input and litter decomposition on SOC sequestration, and explore the contribution of plant and microbial necromass C to SOC sequestration after grazing exclusion. Long-term grazing exclusion improve the structure and function of soil microorganisms by increasing plant carbon inputs, and increase the content and proportion of soil stable organic C (such as mineral-associated organic C, plant and microbial necromass C, etc.), reducing mineralization efficiency of SOC and improving microbial C utilization efficiency, and consequently promoting SOC accumulation. In addition, SOC sequestration shows two trends of "first increasing and then stabilizing" and "first decreasing, following increasing and then stabilizing", which are affected by the initial SOC level. Future studies should be strengthened in the SOC fraction dynamics, the C flow of SOC input, the decomposition process of SOC, and the microbial dri-ving mechanism after grazing exclusion.