## 1 Introduction  
In recent years, global climate change has emerged as a significant environmental issue. Soil is pivotal in controlling the global carbon cycle, serving as the largest carbon reservoir in the terrestrial biosphere [1]. It is estimated that 1500 Pg C is stored in soils as organic matter, three times that in the atmosphere or terrestrial vegetation [2, 3]. Consequently, even minor variations in SOC content can profoundly impact the concentration of carbon dioxide (CO\({}_{2}\)) in the atmosphere [4]. In this context, research on the stability of SOC has become a focal point in scientific studies. Studies indicated that water is a fundamental driver for nearly all chemical and biological processes, including plant growth and survival, photosynthesis, microbial activity, and soil respiration [5]. Based on this, precipitation is considered a primary factor affecting SOC inputs, with different precipitation patterns significantly impacting the function and structure of terrestrial ecosystems. A meta-analysis of precipitation manipulation experiments showed that increased precipitation stimulatessoil respiration by an average of 30%, while reduced precipitation decreases it by 12% [6]. Soil aggregates, as the main reservoirs of SOC, provide physical protection for SOC and are crucial for carbon sequestration [7; 8]. Alternating wet-dry and freeze-thaw cycles, driven by precipitation and temperature, were primary factors affecting aggregate stability [9; 10; 11] and the stability of soil aggregates was vital for maintaining ecosystem functions. It is well-known that surface soils contain a substantial amount of organic carbon, which can be rapidly decomposed and transformed by microorganisms, releasing CO\({}_{2}\) into the atmosphere [12]. However, it is estimated that over 50% of soil carbon is located in subsoil (below 30 cm), where the carbon dynamics may significantly differ from those in the topsoil [13]. For instance, deep soil layers were more susceptible to nutrient inputs and temperature increases than the surface layers [14]. Yet, in soil carbon dynamics research, subsoil studies are sparse and this aspect of soil organic carbon mineralization has been overlooked often. Additionally, the factors influencing carbon mineralization in topsoil and subsoil may differ and research into subsoil carbon mineralization could make a significant contribution to reducing atmospheric carbon in the context of global climate change [15; 16]. Overall, the vertical distribution patterns and regulatory factors of soil protection present significant research value. The mineralization of organic carbon is a vital biogeochemical process occurring naturally in soil, crucial for maintaining soil fertility, nutrient release, mitigating greenhouse gas emissions, and impacting global climate change. The mineralization of organic carbon is influenced by factors such as the quality of SOC and biological elements like microorganisms, both of which are indirectly controlled by abiotic factors like temperature and precipitation [17; 18]. Soil aggregates also play a vital role in the decomposition of SOC. Studies have shown that factors influencing the formation of aggregates also affect the mineralization of SOC [19]. The physical protection ability of soil aggregates for SOC varies with the particle size of aggregates. This highlights the necessity of considering soil structure when predicting future SOC dynamic trajectories. The steppe soils of the Loess Plateau have garnered attention due to their crucial role in China's national carbon budget. Steppe ecosystems, with substantial organic carbon storage, are susceptible to global climate change. The Loess Plateau is located in central China and is the largest concentrated area of loess distribution in China. It falls within the temperate monsoon climate zone, with the eastern and southern parts being characterized by a warm temperate semi-humid monsoon climate, while the northwest part experiences a temperate semi-humid monsoon climate.