## 4 Discussion  
### Effect of Different Land Use Patterns on SOC Distribution  
Land use patterns are among the primary anthropogenic factors influencing changes in SOC content. Variations in vegetation types resulting from shifts in land use patterns can affect the quantity and quality of plant residues entering the soil ecosystem [33]. Additionally, the amount and nature of organic matter migration from surface soil to underlying layers also change, impacting the distribution of SOC within the humus layers [34; 35]. SOC content serves as a crucial indicator for assessing soil quality and fertility [36]. Numerous studies have demonstrated that land use patterns significantly influence SOC storage and accumulation [37; 38]. Some research indicates that the effect of ecosystems on SOC in soil humus layers diminishes with increasing depth [39; 40]. The results of this experiment revealed that the impacts of different land use patterns on organic carbon in the humus layers of mollus varied even at a depth of 60 cm, with the organic carbon content in forested and bushy (FB) soils being higher than that in grassland and farmland. This finding underscores the significant influence of land use patterns on SOC in mollus [41]. In comparison to tillage land, both GB and FB significantly enhanced SOC content in the 0-60 cm layer, with FB demonstrating a particularly positive effect on SOC content increase, aligning with findings from [PERSON] et al. 's study on topsoil in North China. This study reported that plantation soils had the highest SOC content (17.21 g kg\({}^{-1}\)), followed by grassland (17.07 g kg\({}^{-1}\)), both exceeding that of cultivated land (14.04 g kg\({}^{-1}\)). In Northeast China, SOC content is notably elevated (26.55 g kg\({}^{-1}\)) due to low temperatures [42]. Furthermore,  
Figure 8: Correlation coefficients between soil LOC and CPMI. Note: “\(\star\)” means \(p<0.05\), “\(\star\)” means \(p<0.01\), (SOC, soil organic carbon; EOC, easily oxidizable carbon; MBC, microbial biomass carbon; POC, particulate organic carbon; DOC, dissolved organic carbon; CPMI, carbon pool management index; _Kos_, oxidation stability coefficients). \(n=3\). compared to continuous cropping, crop rotation significantly reduced SOC content in soil layers, suggesting that crop rotation, particularly conventional practices, is not conducive to SOC retention in soil humus layers [43]. Tillage disrupts the soil aggregate structure, exposing the organic matter it protects and consequently accelerating the decomposition rate of soil organic matter [44]. Cultivating the same crop in successive years leads to the one-sided consumption of soil nutrients, resulting in an imbalance of soil nutrient levels [45]. Research indicates that reasonable crop rotation can optimize land resource utilization, enhance yield, and promote a balanced use of soil nutrients, although it may also accelerate the decomposition of soil organic matter [46]. Additionally, different vegetation types influence the input of litter and root systems. Compared to fallow grass belts and forest belts, the root systems of farmland are shallower, resulting in lower litter and root biomass input, this limits the capacity to extract nutrients from the soil and import sufficient organic matter, particularly as crop roots are less prevalent in deeper soil layers [47]. In contrast, natural vegetation in fallow grass belts and litter in forest belts provide a more abundant source of organic matter [48]. The accumulation rate of SOC is generally higher in humid areas [49]. Under the climatic conditions of Northeast China, vegetation in grass belts and forest belts is relatively abundant, producing substantial above-ground litter and root exudates annually, which serve as a rich source of SOC [50].