Land Use Impacts on Soil Organic and Inorganic Carbon and Their Isotopes in the Yanqi Basin

Assessments of both soil organic carbon (SOC) and inorganic carbon (SIC) under different land use types are lacking in arid regions. To advance the understanding of soil carbon dynamics and impacts of land use changes, a study was conducted in the central Xinjiang, the Yanqi Basin that had significant land use changes since the 1950s. Soil samples were collected at representative sites under various types of land use and vegetation, and SOC and SIC and their isotopes were measured over the 0–100 cm. This study revealed that both SOC and SIC stocks were the lowest in the desert land, but the highest in the agricultural land. Conversion of native land to cropland has caused a significant increase of SOC in the topsoil, and SIC in the subsoil. Total soil carbon stocks in the 0–100 cm are 11.6 ± 4.8, 44.7 ± 10.4, and 51.2 ± 5.6 kg C m⁻² in the desert land, shrub land, and agricultural land, respectively. On average, soil inorganic carbon counts more than 80% of the total carbon stock in the soil profiles. δ¹³C of SOC shows no significant differences between land use types, but δ¹³C of SIC is much different among land use types, following an order: desert land (−0.6‰) > shrub land (−2.2‰) > agricultural land (−3.4‰). Our finding of SIC increase with depletion of ¹³C in the agricultural land indicates that there has been enhanced accumulation of pedogenic carbonate as a result of cropping.