Influence of Lithology on the Stability of Organic Carbon in Typical Soils of Karst in Northwest China

Soils in Guangxi’s karst region, China, were analyzed to investigate variations in soil organic carbon and their physicochemical characteristics linked to different bedrock development. Four land use types, paddy, dryland, grassland, and scrubland, under the development of two bedrocks (dolomite and limestone) were selected. Soil samples were collected from 0–20 cm depth, and 60-day indoor incubation experiments were carried out. The study revealed that the pH levels in dolomite-developed soils were higher compared to their limestone counterparts, except for scrub soils. The nutrient content in the topsoil of dolomite parent material was also found to be higher. Additionally, the dolomite parent soil had a significantly higher organic carbon (SOC) content than the limestone parent soil. The maximum value of SOC content in dolomite parent soil was 37.96 g·kg⁻¹, which was approximately twice the amount present in the limestone parent soil. The respiration rate of the soil from the limestone parent material was remarkably lower than that of the soil from the dolomite parent material. The C₀/SOC ratio indicated that the dolomite parent soil possessed a higher potential for carbon sequestration. Scrub soils demonstrated the greatest carbon sequestration potential among the four land use types, while dryland soils had the least. The study indicated that lithology significantly affected the soil’s organic carbon content and its potential to sequester carbon. Dolomite soil had higher SOC content and greater carbon sequestration potential. The cultivation and utilization methods of paddy fields among various land use types should be actively promoted to enhance soil organic carbon in karst agricultural land.