Objective The aims were to analyze the relationship between soil aggregate fractions and soil organic carbon (SOC) contents in soils developed from different parent rocks, and to reveal the mechanisms by which parent rock types affect soil aggregate stability and SOC storage in the mountainous areas of southwestern Hubei Province.

Method The yellow soil developed from four typical parent rocks (limestone, conglomerate, sandstone, and shale) in the southwestern mountainous area of Hubei Province was taken as the research object. Through field sampling and indoor analysis, the composition of soil aggregates, stability indicators, and SOC content and storage were determined. Combined with multivariate statistical models, the relationship between the stability level of soil aggregates and the distribution characteristics of SOC in soils with different parent rock developments was analyzed.

Result The soils developed from four types of parent rocks were dominated by <0.25 mm aggregates, with an average proportion of 37.05%. Among them, the soil aggregates developed by shale had the best stability, while those developed by conglomerate had the worst. The mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates in shale-derived soil were significantly higher than those in conglomerate-derived soil, with the increases of 44.35% and 36.73%. Conglomerate-derived soil had the highest erodibility factor (K), whereas limestone- and shale-derived soils demonstrated significantly higher aggregate ratios (AR) compared to other parent materials (P < 0.05). Shale-derived soil contained the highest SOC content (13.86 g kg⁻¹), with SOC stocks significantly exceeding those of conglomerate- and sandstone-derived soils by 33.90% and 61.44%. Correlation analysis combined with partial least squares path modeling (PLS-PM) revealed that soil properties and aggregate characteristics were primary factors influencing SOC storage. The explanatory ratio (R²) of all factors for SOC is 0.87, confirming that parent rock material significantly affects SOC storage through its regulatory effects on aggregate size distribution, physicochemical properties and SOC content.

Conclusion The parent rock is one of the key factors controlling the stability of soil aggregates and SOC storage in the southwestern mountainous areas of Hubei Province. It mainly affects SOC storage by regulating changes in soil properties, aggregate distribution characteristics, and other factors.