Desertification control on soil inorganic and organic carbon accumulation in the topsoil of desert grassland in Ningxia, northwest China

Soil carbon is an essential part of the terrestrial carbon pool, which includes soil organic carbon (SOC) and soil inorganic carbon (SIC). Soils contain a huge amount of inorganic carbon in arid and semiarid regions, which may be a potential source of CO₂ emitted to the atmosphere. Neglecting soil inorganic carbon could result in erroneous or misleading interpretations of the soil carbon pool of arid and semiarid ecosystems. Nevertheless, only a few studies have focused on variations of SIC, or have further used the soil stable carbon isotope to explore the inherent mechanism of SIC variations in semiarid regions. The study was designed to estimate the dynamic of SOC and SIC with the development of desertification in the topsoil. Here, four desertification stages were chosen, including potential desertification (PD), light desertification (LD), severe desertification (SD), and very severe desertification (VSD) stages, to evaluate the horizontal and vertical distributions of SOC and SIC, and the stable carbon isotope (δ¹³C) of SOC and SIC with the desertification development in the topsoil (0–30 cm soil layer). The SOC and SIC contents and storage changed significantly with desertification development. The PD stages had the highest SOC (21.01 mg/hm²) and SIC (11.60 mg/hm²) storage at 0–30 cm, while the contrary result for VSD stages, with the average of SOC and SIC, was 8.27 mg/hm² and 6.15 mg/hm², respectively. The vertical distribution of SIC and SOC has varied sharply with soil depth. The δ¹³C-SIC within the 0–30 cm soil profile in the PD stages were more negative than those in other desertification stages and gradually increased with desertification development. In contrast, the δ¹³C-SOC generally decreased with desertification progress. The entire data (108 soil samples) exhibited that δ¹³C-SIC were significantly and negatively correlated with δ¹³C-SOC and SIC content, while SIC storage was significantly and positively correlated with SOC storage. The results demonstrated that an increase of SOC might be related to enhancing accumulation of SIC. The results of this study provide information about the variation of SIC and SOC with the desertification development and contribute to our understanding of the important role of SIC in estimating the carbon sequestration capacity in the degraded grassland ecosystems in arid and semiarid regions.