Factors influencing and changes in the organic carbon pattern on slope surfaces induced by soil erosion

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).