## 3 Results
### Factors Influencing Soil Organic Carbon Mineralization  
Overall, SOC mineralization in soil profiles showed significant positive correlations with MAP, SOC, POC, and SWOC (\(p<0.01\)) and a significant negative correlation with elevation (\(p<0.05\)) (Figure 8). However, it was observed that SOC mineralization in the 0-50 cm soil layer had a highly significant positive correlation with precipitation (\(p<0.001\)), while the 50-100 cm soil layer was highly significantly correlated with SOC and POC (\(p<0.001\)). It suggested that precipitation primarily controls SOC mineralization in the 0-50 cm soil layer, while the mineralization in the 50-100 cm layer was more closely related to soil-associated carbon. Notably, Clay + Silt showed a significant positive correlation with SOC mineralization in the 50-100 cm soil layer (\(p<0.05\)) but no significant correlation with the 0-50 cm layer. The mineralization of organic carbon in soil aggregates exhibited a highly significant positive correlation with precipitation (\(p<0.001\)), indicating that precipitation was a dominant factor affecting the mineralization of soil aggregates. Additionally, SOC and SWOC showed a highly significant positive correlation with the mineralization of 1-2 mm diameter soil aggregates (\(p<0.001\)) and POC was significantly positively correlated with the mineralization of all sizes of soil aggregates (\(p<0.05\)), suggesting that soil-associated carbon is also a dominant factor in the mineralization of soil aggregates, with a particularly close relationship with 1-2 mm diameter aggregates. The results of Redundancy Analysis (RDA) (Figure 9) showed that the first and second axes explained 99.14% of the relationship between environmental factors and changes in soil organic carbon mineralization in the soil profiles of the Loess Plateau area (a). Among these, MAP was the primary factor influencing the spatial variation in soil organic carbon mineralization, accounting for 84.00% of the explanation (\(p<0.01\)). The vectors of MAP, SOC, POC, and SWOC were quite long and the angles with C\({}_{\text{M}}\) 0-10 cm, C\({}_{\text{M}}\) 10-30 cm, C\({}_{\text{M}}\) 30-50 cm, and C\({}_{\text{M}}\) 50-100 cm were acute, indicating that these indicators had a strong positive impact on soil organic carbon mineralization. MAP and SOC had a greater influence on C\({}_{\text{M}}\) 0-10 cm than on C\({}_{\text{M}}\) 50-100 cm, whereas C\({}_{\text{M}}\) 50-100 cm was more influenced by SOC and POC. Soil pH, elevation, and BD, with obtuse angles, had a negative impact. In Figure 9b, the first and second axes explained 99.14% of the relationship between environmental factors and changes in organic carbon mineralization of soil aggregates in the Loess Plateau area. Here, MAP was the main factor affecting the spatial variation in organic carbon mineralization in soil aggregates, explaining 83.00% (\(p<0.01\)). The  
Figure 8: Correlation analysis between soil organic carbon mineralization in soil profiles (**a**) and soil aggregates (**b**) of the Loess Plateau and environmental and soil factors (* \(p<0.05\), ** \(p<0.01\), and *** \(p<0.001\)). Blue indicates a positive correlation, while red indicates a negative correlation. MAP, mean annual precipitation; MAT, mean annual temperature; BD, bulk density; POC, particulate organic carbon; ROC, readily oxidizable carbon; SWOC, water-soluble organic carbon; MWD, mean weight diameter. in the structural equation analysis, the model exhibited high fit (\(\chi^{2}\) = 4.023, df = 4.000, \(p\) = 0.403, rmsea = 0.025) (Figure 10). The spatial variation in soil organic carbon was explained by 80.0%, with MAP having the most significant impact, with a factor coefficient of 0.89 (\(p\) < 0.001). The spatial variation in soil organic carbon mineralization in the 0-10 cm layer was 88.0%, with the most influential variable being MAP, followed by SOC (\(p\) < 0.05). For the 50-100 cm layer, the spatial variation in soil organic carbon mineralization was 77.0%, most influenced by Clay + Silt, followed by POC (\(p\) < 0.05).