Land use-driven shifts in labile carbon fractions regulated total profile sequestration of soil organic and inorganic carbon in arid environments

Effective climate change mitigation through land-based strategies requires maximizing soil carbon (C) sequestration across land uses and management practices. Yet, land-use and management impacts on soil C and nitrogen (N) fractions and their distribution in soil profiles in water-limited environments remain elusive. We evaluated various labile and stable pools of soil C and N at 0–15, 15–30, and 30–60 cm depths under four long-term land uses – continuous alfalfa and tall fescue systems, a conventionally managed annual cropping system, and cottonwood orchard – to understand land use-driven changes in soil C fractions in different depths, and total profile C sequestration. Results showed that C and N fractions were allocated differently across depth layers, suggesting divergent mechanisms of C sequestration at different depths. Perennial systems increased labile and stable C pools, specifically at 0–15 cm, thereby supporting biologically mediated soil organic C (SOC) sequestration. The annual cropping system accumulated greater mineral-associated organic C (MAOC) and inorganic C at 30–60 cm, mediated by the physicochemical pathway of C formation and stabilization. At 0–60 cm, soil inorganic N and potentially mineralizable N (PMN) were 2.4–7.3 and 3.8–8.4 times higher, respectively, under annual crops than other land uses. The profile distribution of labile N and C fractions relative to MAOC played a crucial role in SOC sequestration in various depths. The potential of arid soils to sequester C varied with vegetation type and land use. Management practices should focus on optimizing the distribution of labile C and N throughout the profile to promote microbial activity and enhance soil C sequestration. • Soil profile C and N distribution varied with diverse land-use systems. • Soil mineralizable C and N significantly influenced depth-wise organic C distribution. • Perennial crops promoted soil C storage in surface soils via biological processes. • Annual cropping supported the physicochemical pathway to sequester C in subsurface soils.