SOC stabilisation shifts from carbon accumulation in temperate soils to mineral association in subtropical soils

Soil organic carbon (SOC) is operationally partitioned into particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) to infer soil carbon persistence and sensitivity to disturbance or management. Yet the combined roles of climate, mineralogy, and land use in shaping these fractions remain unresolved across continental gradients. Here, we analysed 249 Australian topsoils from 65 paired sites along a 550 mm rainfall isohyet. Samples were grouped into four climate–texture clusters (Subtropical Coarse, Subtropical Fine, Temperate Coarse, Temperate Fine) to disentangle the effects of thermal and hydrological regimes, soil properties, and land use on SOC partitioning and stabilisation. Subtropical soils consistently exhibited a high proportion of MAOC (fMAOC ≈ 0.8) despite low SOC stocks, reflecting preferential retention of mineral–organic interactions under carbon-limited and water-stressed conditions. In contrast, temperate soils stored greater SOC and POC, indicating higher carbon inputs and slower decomposition. In subtropical fine-textured soils, agriculture elevated fMAOC through microbial activity and nutrient inputs, yet this occurred alongside depleted SOC and POC, highlighting a trade-off between stabilisation efficiency and carbon stock depletion. Across all clusters, land use effects were detectable but secondary to climate and mineral properties. These findings show that temperate and subtropical soils follow contrasting carbon stabilisation pathways: temperate systems store more carbon overall, while subtropical systems allocate a larger share of their carbon to mineral-associated carbon. Our climate–texture framework highlights region-specific management priorities: enhancing mineral–organic interactions through increased root inputs and organic or mineral amendments in subtropical soils, and protecting vulnerable carbon stocks through reduced disturbance and residue retention in temperate systems. • SOC stability is context dependent, not universal. • Temperature and clay jointly control particulate and mineral-associated pools. • Agriculture reduces both particulate and mineral-associated carbon stocks. • Soil carbon responses to land use depend on climate and texture. • The climate–texture framework identifies region-specific pathways.