## 4 Discussion
### Effect of Different Land Use Patterns on Soil LOC  
DOC and EOC are the fractions with the fastest turnover rates in SOC and are vital components of the soil labile organic carbon pool [55]. DOC and EOC are regarded as the primary energy sources for soil microorganisms, which are significantly influenced by factors such as land use practices, vegetation type, temperature, and humidity [56], these fractions can respond rapidly to changes in soil management strategies, making them important indicators for assessing alterations in soil organic carbon, soil fertility, and soil quality. Previous research has shown that converting farmland to grassland and woodland can significantly increase the levels of DOC and EOC in the soil, which aligns with the findings of this study [57; 58]. On the one hand, the decomposition of plant residues directly facilitates the formation of the labile organic carbon pool in the soil. On the other hand, plant residues enhance the activity of soil microorganisms, thereby promoting the conversion of plant residue carbon into soil labile organic carbon [59]. As an important fractions of soil labile organic carbon, MBC is sensitive to changes in soil environment and is an important indicator reflecting soil microbial activity and organic carbon quality [60]. In this study, FB significantly increased the content of MBC in soil. This result may be due to the decomposition characteristics of litter in soil. Since plant residues are mainly composed of cellulose, hemicellulose, lignin and other fractions, it takes a certain period of time for them to be fully degraded in soil before they can become nutrients directly utilized by soil microorganisms, so the microbial population in the soil also increases significantly [61]. As a constituent of LOC, DOC was significantly influenced by hydrothermal conditions. Favorable hydrothermal conditions during the rainy season enhance the metabolic rates of microorganisms and vegetation, thereby sustaining high levels of DOC in the soil [62]. EOC and MBC were notably affected by land use patterns, soil depth, and their interactions. This may be attributed to the fact that EOC and MBC are components of soil carbon that exhibit rapid turnover rates and respond quickly to changes in soil management practices and surrounding environmental conditions [63]. In this study, the concentrations of EOC and MBC were lowest in cultivated land and highest in the forest belt and grass belt. The increased DOC content in the grass belt (GB) and forest belt (FB) may be due to lower vegetation density, sufficient light and heat conditions, and relatively fast vegetation regeneration, which collectively enhance the litter input both on the surface and underground. Prolonged cultivation in agricultural land leads to significant soil nutrient depletion, which hampers microbial growth, inhibiting both their quantity and activity, and consequently reducing the source of LOC [64]. Furthermore, researchers found that tillage disrupts the aggregate structure, releasing organic carbon previously protected by this structure, which facilitates microbial utilization of organic carbon and accelerates the mineralization and decomposition of organic carbon, ultimately resulting in a decrease in the content of labile organic carbon [65]. As DOC serves as the primary carbon source directly utilized in microbial growth, its concentration reflects the carbon availability for soil microorganisms, which may be a crucial factor in maintaining high EOC and MBC levels in deeper soil layers [66]. [PERSON] posited that the soil's ability to stabilize organic carbon is pivotal for SOC accumulation; if this ability is low, the risk of loss for input organic carbon increases [67]. POC refers to the organic carbon bound to sand particles (53-2000 \(\upmu\)m), consisting of incompletely decomposed root systems and plant and animal residues. It plays a crucial role in soil organic carbon turnover and aggregation and can function as a sensitive indicator reflecting the extent of soil disturbance [68].