Soil carbon dioxide dynamics in deep profiles under erosional and depositional conditions on the Chinese Loess Plateau

Soil erosion alters soil structure, hydrology, and carbon dynamics, yet the mechanisms driving subsoil CO₂ emissions are not well understood, particularly in the highly erodible Chinese Loess Plateau. This study investigated the effects of erosion and deposition on vertical CO₂ fluxes and associated controls in 0–200 cm soil profiles of representative check dam systems. We conducted monthly measurements of CO₂ flux, soil temperature, moisture, physicochemical properties, and δ¹³C signatures from June to October 2022. Although total soil organic carbon (SOC) stocks were similar between erosional and depositional sites, their vertical patterns differed: SOC exhibited deeper accumulation at erosional sites but was enriched near the surface at depositional sites. Deeper soil layers (140–200 cm) in depositional sites also exhibited higher soil inorganic carbon (SIC) stocks than erosional sites, likely due to carbonate accumulation. CO₂ fluxes were significantly higher at depositional sites (11.77 – 146.58 μmol m^–2 s^–1) than at erosional sites (1.25 – 34.58 μmol m^–2 s^–1), with subsoil emissions contributing up to 33.4 % of total fluxes. Surface CO₂ fluxes were mainly influenced by temperature, SOC, and pH, while subsoil fluxes were regulated by temperature, moisture, SOC, and SIC. δ¹³C signatures indicated SOC mineralization as the dominant CO₂ source at erosional sites, whereas carbonate-derived CO₂ was dominant in depositional subsoils. These findings reveal the crucial role of geomorphic processes and subsoil conditions in regulating CO₂ emissions and provide a scientific basis for improving soil carbon management in erosion-prone regions.