Soil aggregate stability in karst peak-cluster depressions: How do organic–inorganic cements work together?

Abstract

Karst peak-cluster depressions are among the most ecologically fragile regions in China. Organic–inorganic cementing agents increase soil aggregate stability, but their mechanisms of action are not fully understood. This study assessed the relationships between these cementing agents and soil aggregate stability were assessed by analyzing organic carbon (SOC) and calcium forms in each aggregate across five typical land-use types: cultivated land (CL), citrus plantation (CP), plantation forest (PF), coppice forest (CF), and secondary forest (SF) in the southwest karst region of China. The results showed that the mean weight diameter (MWD) of soil aggregates was influenced by the type of land use and depth of the soil layer, and was the highest in the surface soil of SF, while the subsoil of CL was the lowest. The SOC content in each aggregate size class decreased with depth, with the surface macroaggregates (>0.25 mm) containing more SOC; which was the highest in SF and lowest in CL. Polysaccharide-C dominated CL, CP, and SF soils, while Aromatic-C was predominant in PF and CF and served as the key functional group controlling organic carbon and aggregate stability. The calcium content was the highest in SF and lowest in CL, with acid-soluble calcium (Ca-As) being the most prevalent form across land use types. Among soil aggregate fractions, SOC content and Ca-As exhibited the strongest correlations with aggregate stability metrics. Notably, SOC and Ca-As in 2–3 mm aggregates were the primary contributors to soil aggregate stability, both parameters exerted direct effects on the mean weight diameter of MWDwet, with SOC playing a predominant role (R² = 0.680). The study indicated the key mechanisms by which organic–inorganic cementing substances synergistically regulate soil aggregate stability, offering critical data support and scientific guidance for soil and water conservation in karst areas.