Land use change impacted profile distributions of soil organic carbon fractions in the Yanqi Basin

Soil organic carbon (SOC), the largest carbon pool on land, plays an important role in the global carbon cycle. The global SOC pool is proximately 1500 Pg C in the topsoil of 1 m, which is two times of the global terrestrial biomass. Thus, small changes in the SOC stock may have large impacts on the atmospheric CO₂ concentration. Therefore, the stability of SOC is critical to the global carbon cycle and climate change. 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.

The researchers carried out a study of land use changes since 1950, i.e., converting native land to cropland in a typical arid area, the Yanqi Basin in Xinjiang, northwest China. Soil samples in the study were taken from 1 m soil profiles in both native land and cropland, and labile, semi-labile, and recalcitrant SOC fractions were determined for examining the vertical distributions of SOC fractions, and evaluating the impacts of land use change.

The results show that all SOC fractions have a gradual decrease with the soil 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 a longer-term SOC storage. The study was published in Catena in April 2014.