The mineralization of soil organic carbon (SOC) is a critical process in the soil carbon cycle. This study aimed to investigate the vertical distribution characteristics and mineralization dynamics of SOC in soils and their aggregates across different steppe types in the Loess Plateau (LP). Soil profiles from three steppe types under varying precipitation gradients were selected: meadow steppe (MS), typical steppe (TS), and desert steppe (DS). A 60-day controlled laboratory incubation study was conducted for carbon mineralization and the influence of climatic and soil properties on SOC mineralization was analyzed. The results showed that the SOC content and cumulative mineralization (C_M) in 1–2 mm aggregates were higher than in other particle sizes; SOC content and C_M followed the order MS > TS > DS and both decreased significantly with increasing soil depth. Correlation analysis revealed that precipitation significantly affected aggregate mineralization (p < 0.001) and that mineralization in the 1–2 mm aggregates was more closely related to mean annual precipitation (MAP), SOC, and water-soluble organic carbon (SWOC). Precipitation primarily controlled SOC mineralization in the 0–50 cm soil layer, while SOC mineralization in the 50–100 cm layer was influenced by soil-related carbon content. Structural Equation Modeling indicated that precipitation influences the mineralization of organic carbon in topsoil indirectly through its direct impact on SOC. In the context of global warming, the SOC turnover rate in high-precipitation areas (MS) was faster than in low-precipitation areas (TS, DS), necessitating greater attention to soil carbon dynamics in these regions.

The purpose of this study was to determine the mineral-associated organic carbon (MOC) and its relationship to clay minerals under different temperatures and precipitation. We selected three typical grassland transects in China: Titanium Plate (TP), Mongolian Plate (MP), and Loess Plate (LP) with natural temperature gradients. Along the transect, there is a gradient in the precipitation between the various types of grasslands. The surface soil (0–10 cm) was sampled to determine the MOC. Clay minerals were charactered by X-ray diffraction (XRD). According to the findings, the MOC content increased with decreasing temperature (5.41–14.89 g/kg). MOC had a positive correlation (r = 0.67) with the amount of clay mineral content. In the large-scale study of transects, precipitation masks the effect of temperature change on the MOC to a certain extent. It indirectly affected the MOC content by affecting the mixed-layer illite/smectite (I/Sme) content, and this effect was strongest at the lowest temperature TP (r = −0.73). Except for precipitation, CaO in the soil can affect soil organic carbon (SOC) stability by influencing the pH and I/Sme. The amount of bacteria increased as a result of I/Sme, and the influence of bacteria on the MOC was surpassed only by the soil pH. Climate and clay mineral composition characteristics affected the MOC to a certain extent. Among them, the effect of precipitation change on the MOC is higher than temperature, but it has little effect on soil with a higher weathering degree and CaO content.