Soil microbial biomass, primarily composed of bacteria and fungi, features a short turnover time and rapid rate, responding promptly to alterations in land use patterns and management. MBC and nitrogen regulate the C and N cycles in terrestrial ecosystems and play a crucial role in nutrient transformation and supply. This not only reflects soil microbial activity but also characterizes the available LOC fractions in the soil [17]. [PERSON] et al. [18] confirmed that shrubs and forestland can enhance SOC storage more effectively than farmland. However, [PERSON]'s study indicated that the contents of MBC and microbial biomass nitrogen (MBN) in farmland are higher than those found in grassland and forestland. In the wheat-pearl millet farmland, the MBC and MBN contents in the 0-10 cm soil layer were measured at 418.2 \(\mu\)g/g and 52.9 \(\mu\)g/g, respectively; in con trast, the lowest values were observed in teak forestland, with measurements of 281.2 ug/g for carbon and 36.02 ug/g for nitrogen, while grassland exhibited slightly higher values than teak forestland, at 298.3 ug/g and 37.28 ug/g, respectively [19]. It suggests that soil LOC fractions are highly sensitive to land use patterns, and this sensitivity is not dependent on the soil's inherent organic carbon reserves [20]. The spatial heterogeneity of SOC content leads to a slow response to subtle variations in the soil environment [21]. Measuring SOC and LOC content does not provide a comprehensive or real-time assessment of changes in soil quality [22]. This limitation highlights the necessity for more holistic approaches that capture the complexity of soil health and its evolution. In this context, CPMI, CPI, and CAI have emerged as innovative tools that address these challenges. By integrating these indices, the CPMI enables dynamic and continuous monitoring of the soil carbon pool, which is essential for understanding the various factors that influence soil health. Furthermore, the CPMI facilitates a detailed examination of how different elements, such as climate change and land use patterns, affect soil carbon dynamics [23]. This capability is particularly important as it allows researchers and land managers to effectively quantify and analyze fluctuations in soil organic carbon across diverse soil environments. By employing the CPMI, stakeholders can achieve a more timely and accurate characterization of the changes occurring within the soil carbon pool, ensuring that their strategies for soil management and conservation are informed by robust data and insights [24]. Additionally, the oxidation stability coefficient (\(K_{OS}\)) serves as an effective parameter for measuring changes in the LOC fractions of soil and its fertility. \(K_{OS}\) gauges soil oxidation stability and is related to different factors, such as the difficulty of soil organic carbon decomposition and nutrient release [25]. A larger \(K_{OS}\) value indicates greater oxidation stability, signifying that the decomposition of soil organic carbon is more challenging and nutrient release is relatively slow, which positively contributes to maintaining soil fertility [26]; conversely, a smaller \(K_{OS}\) value reflects lower oxidation stability, suggesting that the decomposition of soil organic carbon is easier and nutrient release is faster, potentially jeopardizing the long-term maintenance of soil fertility [27]. This study utilized mollusids from Northeast China as the test soil and, based on long-term positioning experiments, analyzed and compared the effects of five different land use methods on the organic carbon and labile organic carbon components of soil humus layers at depths of 0-20 cm, 20-40 cm, and 40-60 cm. This study conducted an in-depth examination of soil organic carbon and its active components, as well as the distribution characteristics of CPMI and \(K_{OS}\) within the black soil humus layer, under different land use patterns.