Impact of land use change on profile distributions of soil organic carbon fractions in the Yanqi Basin

Land use change is recognized as one important driving force for soil organic carbon (SOC) dynamics. The arid regions in China have experienced significant land use changes over the past decades. A study was carried out to evaluate the impacts of land use change on SOC fractions in the Yanqi Basin, northwest China. Soil samples were collected from 24 profiles in cropland and native land, and labile, semi-labile, and recalcitrant organic carbon were measured. All SOC fractions showed a gradual decrease with depth over the 0-100 cm in the native land. However, SOC fractions in the cropland revealed uniform distributions over the 0-30 cm and 30-100 cm. On average, labile, semi-labile, and recalcitrant carbon contents in the cropland were 2.2 ± 0.3 (1.3 ± 0.4), 1.5 ± 0.4 (0.7 ± 0.3), and 8.5 ± 2.0 (3.1 ± 1.8) g kg− 1 over the 0-30 cm (30-100 cm), respectively. Converting native land to cropland resulted in significant increases of recalcitrant (2.0 kg m− 2), semi-labile (0.3 kg m− 2), and labile carbon (0.3 kg m− 2) over the 0-30 cm. The proportion of recalcitrant SOC stock increased from 59.9% in the native land to 64.8% in the cropland. This study suggests that converting native land to cropland in arid region not only enhances SOC stocks but also leads to longer-term SOC storage.