Effects of Long-Term Land Use Patterns on Labile Organic Carbon Fractions and Carbon Pool Management Index of Mollisols Humus Layers  
[PERSON]  
1 College of Resources and Environment Sciences, Jilin Agricultural University, Changchun 130118, China; [EMAIL_ADDRESS] (X.D. ); [EMAIL_ADDRESS] (W.C.)1 College of Resources and Environment Sciences, Jilin Agricultural University, Changchun 130118, China; [EMAIL_ADDRESS] (X.D. ); chengweltonghua@163.  
soil [1]. The estimated global stocks of SOC, extending to a depth of 2 m, are approximately 2400 Gt C [2], which is three times the amount of carbon present in the atmosphere [3]. The global carbon cycle was influenced by the interactions among SOC, the biosphere, and the atmosphere; SOC frequently exchanges carbon dioxide with the atmosphere, with approximately two-thirds of the carbon in terrestrial ecosystems being actively exchanged through SOC [4]. Consequently, changes in SOC can influence atmospheric CO\({}_{2}\) concentrations, thereby impacting the global carbon cycle [5]. This indicates that even minor fluctuations in SOC stocks can significantly affect atmospheric CO\({}_{2}\) levels and contribute to climate change [6; 7]. The primary factors influencing changes in SOC levels include land management practices, land use changes, and climate change [8]. Therefore, it is crucial to prioritize land use strategies that enhance organic carbon levels and contribute to climate change mitigation. The stability and decomposability of SOC are influenced by a multitude of factors. The rate of decomposition of soil organic matter is contingent upon the chemical composition of the input materials, including plant litter and exogenous organic matter [9]. Variations in land use patterns lead to differences in litter types, which directly affect the quantity, quality, and rate of carbon input, thereby significantly impacting biomass and organic carbon reserves. Consequently, the chemical properties and recalcirance of substances introduced into the soil play a critical role in their sequestration, influencing the accumulation of SOC, its composition, structure, and its vital role in nutrient cycling and carbon emissions to the atmosphere [10]. Additionally, the conversion and accumulation of plant biomass into SOC are markedly affected by factors such as crop types and land use. The intricate interactions among plant biomass, soil microorganisms, soil organic matter, and mineral matrices, along with their dependence on land use and vegetation types, render it exceedingly challenging to elucidate the processes and mechanisms underlying the formation and stabilization of soil organic matter [11]. Soil labile organic carbon (LOC) serves as the principal energy source for plants and soil microorganisms and is directly correlated with nutrient cycling and bioavailability. It is utilized as a sensitive indicator of variations in soil quality. labile organic carbon fractions, such as dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC), particulate organic carbon (POC), and microbial biomass carbon (MBC), are highly susceptible to the influences of planting patterns, land use practices, and agricultural management measures [12; 13; 14]. In contrast to maize-soybean rotation, continuous maize cultivation inputs more biomass carbon into the soil, resulting in a higher content of soil particulate organic matter (POM) [15]. Studies examining land use patterns on the Loess Plateau indicate that the response rates of EOC, light fraction organic carbon (LFOC), DOC, and POC to different land use patterns are more rapid than those of SOC. Furthermore, the total amounts of SOC and EOC in grassland and forestland exceed those in farmland [16]. The transformation of evergreen broadleaf forests into tea and bamboo plantations reduces the concentrations of water-soluble organic carbon (WSOC), light/heavy-fraction organic carbon (LFOC, HFOC), and humic carbon (HC) [13].