Weathering intensity and mineral association facilitate the accumulation of soil organic carbon along an alpine toposequence

Alpine and other cold region ecosystems store globally important soil organic carbon (SOC) stocks that are vulnerable to warming. Therefore, determining the mechanisms that regulate SOC persistence is key to identifying the susceptibility to loss. In this study, we examined how climate, mineralogy and soil properties shape SOC accumulation, partitioning between particulate organic matter (POM) and mineral-associated OM (MAOM) and the associated C functional group composition along an alpine toposequence (1100 m to 2200 m elevation) in Kosciuszko National Park, Australia. Bulk SOC increased seven-fold (from 20.1 to 148 g C kg −1 soil) from 1100 to 1700 m, before declining over two-fold to 2200 m. Across all elevations, SOC was predominantly mineral associated (ca. 64%). Higher SOC concentrations coincided with a greater degree of mineral alteration and abundance of reactive minerals, consistent with enhanced MAOM formation. Despite large differences in SOC concentrations, the proportional distribution of C functional groups remained consistent across elevations and fractions, indicating that the accumulation and persistence of SOC was not associated with the selective preservation or loss of specific biomolecules. These results suggest that sensitivity of alpine SOC cannot be inferred from climate or productivity alone – it also depends on how pedogenesis and weathering regulate the accumulation of OC as MAOM. Consequently, our study provides evidence that mineral associations are driving the accumulation and stabilisation of the SOC pool and that these associations may help explain differences in warming sensitivity among alpine and other cold-region ecosystems.