Land use impacts on soil organic carbon stratification and sequestration in a karst region of Guizhou, China

This study focuses on the vulnerability of soil carbon storage and the ecological restoration processes in karst regions. Given that land-use changes significantly influence the stability and functionality of soil carbon pools, this study investigated the vertical and temporal dynamics of soil organic carbon (SOC) and its labile fractions under five land-use types in a fragile karst region of Guizhou, China. Soil samples from five depths (0–100 cm) were collected in 2019 and 2020 from agricultural land, abandoned land, shrubland, and middle-aged and over-mature Pinus massoniana forests. Analyses showed that SOC, readily oxidizable organic carbon (ROOC), and water-soluble organic carbon (WSOC) decreased significantly with depth (P < 0.001). Mean SOC was 10.51 g·kg^-1, with the highest topsoil content in agricultural land (13.24–15.14 g·kg^-1). Shrubland exhibited the highest surface carbon sequestration efficiency, indicated by a Carbon Management Index (CMI) of 149.37 in the 0–20 cm layer and higher carbon pool activity (L=1.31 at 0–40 cm). Redundancy analysis identified total potassium, total phosphorus, and ROOC as key factors governing CMI variability (97.75% variance explained). The results advocate for stratified land management promoting shrubland for surface carbon sequestration and adopting reduced tillage in agriculture to enhance carbon retention in karst ecosystems.