The "Grain for Green" project disrupts the original sediment distribution pattern on eroded slopes, leading to changes in the lateral transport and vertical deposition of organic carbon. The organic carbon fraction can further enhance our understanding of the dynamics of soil carbon pools during deposition, which can help enhance understanding of the role of soil erosion in the global carbon cycle. On the Loess Plateau, we chose retreating slope (grasslands) and original slope (cultivated land) for our study. Through field sampling combined with an indoor test analysis, we hope to explain dynamic changes in the soil carbon pool on the retired slope, in response to deposition resulting from eroded material. It was found that as the cultivated land was retired to grassland, the sediment transport deposition pattern on the slope altered from whole-slope erosion to alternating erosion-deposition changes. Vegetation restoration changed the composition of the soil carbon fraction: the ratio of grassland particulate organic carbon (POC) to total organic carbon increased from 48.62% to 61.36%, and the sensitivity index of the carbon fraction changed from light fraction organic carbon (LFOC) to dissolved organic carbon (DOC) following the transformation of cropland to grassland. Partial least squares path modeling (PLS-PM) was further conducted to quantify the effects of erosive sediment texture, carbon fraction, and stoichiometry on soil organic carbon (SOC). Erosive sediment texture was a key variable influencing SOC in cultivated soils (path coefficient:0.852), whereas the carbon fraction on the grassland slope had the greatest influence on the organic carbon (path coefficient:0.830). The soil erosion modulus negatively affected erosive sediment texture on both cultivated and grassland slopes. Studies have shown that on severely eroded slopes, attention should be paid to the transport of sediment and organic carbon allochthonous caused by erosion.When erosion intensity decreases, it may be more effective to reduce organic carbon mineralization and increase carbon sequestration by enhancing the physical protection of carbon components and reducing the accessibility of soil microorganisms, giving full play to the role of soil and water conservation in achieving the global sustainable development goal of carbon neutrality. This study provides a scientific support for further supplementing the turnover mechanism of the carbon fraction in the soil carbon cycle (in the context of soil erosion).

“退耕还林”工程破坏了侵蚀坡面原有的沉积物分布格局，导致有机碳的横向运移和垂直沉降发生变化。有机碳部分可以进一步增强我们对沉积过程中土壤碳库动态的理解，这有助于增强对土壤侵蚀在全球碳循环中作用的理解。在黄土高原上，我们选择了后退坡地（草地）和原始坡地（耕地）进行研究。通过现场采样与室内测试分析相结合，我们希望解释退役斜坡土壤碳库因侵蚀物质沉积而发生的动态变化。研究发现，随着耕地退耕还草，坡面上泥沙运移沉积模式由全坡侵蚀转变为侵蚀-沉积交替变化。植被恢复改变了土壤碳组分的组成：草地颗粒有机碳（POC）占总有机碳的比例由48.62%增加到61.36%，碳组分的敏感指数由轻组分有机碳（LFOC）变化农田转变为草地后溶解的有机碳（DOC）。进一步进行偏最小二乘路径模型（PLS-PM）来量化侵蚀性沉积物质地、碳分数和化学计量对土壤有机碳（SOC）的影响。侵蚀沉积物质地是影响耕地土壤SOC的关键变量（通径系数：0.852），而草地坡度上的碳分数对有机碳的影响最大（通径系数：0.830）。土壤侵蚀模数对耕地和草地斜坡的侵蚀沉积物质地产生负面影响。研究表明，在侵蚀严重的边坡上，应注意侵蚀引起的泥沙和外来有机碳的迁移。当侵蚀强度减弱时，通过加强物理保护，可能更有效地减少有机碳矿化，增加碳汇减少碳成分，减少土壤微生物的可及性，充分发挥水土保持在实现碳中和全球可持续发展目标中的作用。本研究为进一步补充土壤碳循环（土壤侵蚀背景下）碳组分的周转机制提供了科学支撑。