[Impacts of exogenous carbon inputs on soil carbon budget and the underlying regulatory mechanisms.]

Soil is one of the largest carbon reservoirs in terrestrial ecosystems. Soil carbon sequestration plays a critical role in mitigating global climate change. Exogenous carbon inputs are key drivers regulating soil organic carbon mineralization and stabilization processes, which are widely present in both natural ecosystems and agricultural management practices. However, the effects of exogenous carbon inputs on soil carbon budget remain highly uncertain. Such exogenous carbon inputs may enhance carbon accumulation, but can also suppress or accelerate the decomposition of soil organic carbon through priming effects. We systematically synthesized the major mechanisms by which exogenous carbon inputs influence soil carbon turnover and stability, focused on the transformation and allocation pathways of exogenous carbon in soil, as well as the formation efficiency. Furthermore, we summarized the key regulatory factors, including microbial processes, mineral protection, and soil physical mechanisms. On this basis, we discussed the main controversies and limitations in current research and proposed future research directions, aiming to provide a theoretical foundation for enhancing soil carbon sink capacity.