## 4 Discussion
### Effects of Agricultural Land Use Change on SOC Stability and Soil Fertility  
Some studies have suggested that the labile carbon content proportion within SOC may provide a more accurate reflection of the current state of the soil carbon pool than merely assessing the absolute amount of active carbon [71]. This observation is significant for understanding the dynamics of soil carbon, as it emphasizes the importance of labile carbon in characterizing soil health [72]. Moreover, the ratio of labile carbon to SOC can effectively diminish the effects of SOC content on the measurements of active carbon [73]. Thus, a focus on LOC is critical since its high content is generally beneficial for soil quality due to its rapid decomposition rate, while a lower content promotes carbon sequestration [74]. This highlights a nuanced balance between soil health and its capacity to store carbon,suggesting that both high and low LOC levels play vital roles, depending on the context [72]. The LOC/SOC ratio is recognized as an important measure of organic carbon stability in soil; it was noted that the LOC/SOC ratio was greater in the upper soil layer compared to the deeper layers. These findings align with earlier research [75]. Interestingly, the results of this study indicated that, although no significant difference was observed in the LOC/SOC ratio between tillage and non-tillage treatments, notable variations in both SOC and LOC contents were evident across different land use types, this finding challenges the reliance on the LOC/SOC ratio as the sole indicator for assessing soil organic carbon stability and quality, suggesting that additional factors should be considered. Furthermore, POC constituted the largest share of LOC, indicating its significance in the overall carbon stability within the soil. The distribution ratio of soil POC proved to be an effective measure for reflecting the intensity of organic carbon stability across different land use patterns while minimizing the impact of organic carbon variance [76]. Notably, the observed increase in SOC is primarily linked to the rise in soil POC, which is known to range from 30% to 85% [77]. The findings of this study, which ranged from 55.03% to 78.84%, align closely with the existing literature, thereby reinforcing the importance of POC in understanding soil carbon dynamics.  
However, the components of LOC are significantly influenced by agricultural land conversion, particularly the MBC/LOC ratio. MBC/SOC, also referred to as microbial entropy, effectively characterizes microbial carbon conversion efficiency and soil carbon loss, and can be utilized to infer the availability and stability of carbon [78]. A larger MBC/SOC indicates a higher utilization rate of organic carbon. Due to the lower MBC/LOC ratio, which does not provide sufficient nutrients to crops from organic carbon decomposition, additional fertilizers are required to enhance the supply of available nutrients to crops. This reliance on fertilizers may further exacerbate soil quality degradation and negatively impact the sustainability of agricultural land. DOC/LOC serves as an indicator of the stability of soil organic carbon; a higher proportion of DOC in organic carbon corresponds to increased activity and stability, facilitating utilization and enhancing soil fertility [79]. In contrast to [PERSON]'s [57] findings on paddy soil, it is evident that the proportion of LOC is influenced by land use patterns, organic matter input, and soil type. EOC/LOC is commonly used to represent the amount of organic carbon in soil that is readily decomposed through microbial oxidation, also known as the organic carbon oxidation rate [79]; therefore, greater attention should be directed towards changes in soil carbon in the deeper layers below the humus layer, as influenced by land use patterns [80].