Characteristics of soil organic carbon fractions and key factors in high-latitude cold-arid wetlands: a multi-type comparison in the Baotou Yellow River Basin

Wetlands act as essential global carbon sinks. In high-latitude cold-arid regions, soil carbon sequestration and SOC fraction stabilization may be uniquely regulated by regional conditions; however, carbon sequestration characteristics can vary substantially among wetland types. This study assessed the distribution of soil organic carbon (SOC) fractions and their controlling factors in four representative wetland types: riverine (RW), lacustrine (LW), artificial (AW), and marsh (MW). Topsoil (0–20 cm) and subsoil (40–60 cm) samples were analyzed for SOC and its fractions (particulate organic carbon, POC; mineral-associated organic carbon, MAOC), along with their associations with biotic and abiotic drivers. A significant interaction between wetland type and soil depth was observed,. In topsoil, MW had the highest POC and SOC contents (13.9 and 15.5 mg g - ¹), whereas RW and LW subsoils showed the highest soil carbon accumulation, with POC and SOC contents of 22.9.5-24.7 and 18.5-19.5 mg g - ¹, respectively. Furthermore, linear mixed-effects models (LMM) revealed divergent stabilization pathways: POC accumulation was primarily predicted by biogeochemical factors, with total nitrogen (TN) as the dominant positive driver (R 2m = 0.75). In contrast, MAOC accumulation was controlled by soil hydrology and the redox state, showing a strong negative correlation with saturated hydraulic conductivity (Ks, R 2m = 0.36). These findings elucidate type- and depth-specific SOC partitioning mechanisms, contributing to the knowledge for enhanced soil carbon management and ecological conservation in Yellow River wetlands.