Drivers and spatial distribution of soil organic carbon and total nitrogen in China's drylands

Aridity has serious impacts on the pools, fluxes and processes of terrestrial carbon (C) and nitrogen (N) cycles. Drylands, with high aridity, also being particularly sensitive to global shifts, require accurate estimation of soil organic carbon (SOC) and total nitrogen (STN) pools for a comprehensive grasp of dryland C and N dynamics within the global C and N cycle. Hence, SOC and STN of 2895 soil samples combined with 11 selected environmental covariates were collected from 175 sampling sites in the drylands of China, the spatial distributions of SOC density (SOCD) and STN density (STND) were mapped with best-performing random forest model. SOC0- 100cm and STN 0-100cm stocks were 30.84 and 2.02 Pg, respectively. Mean annual precipitation and soil moisture were identified as the primary drivers of SOCD 0-30cm and STND 0-30cm , while mean annual temperature influenced SOCD 30-50cm and STND 30-50cm , and soil clay content affected SOCD 50-100cm and STND 50-100cm . Future warming is projected to reduce both SOCD and STND, whereas increased precipitation is expected to have a positive effect on both variables in drylands. Under future climate scenarios outlined by the Representative Concentration Pathway, declines in both SOCD and STND are anticipated, with STND exhibiting a more pronounced decrease. A 1.5 degrees C increase in temperature had the greatest effect on SOCD, while a 15 % decrease in precipitation had the greatest effect on STND. In conclusion, the spatiotemporal estimations presented in this study serve as a valuable supplement to existing SOC and STN stock measurements, enhancing our understanding of C and N cycling in drylands. Our findings are instrumental for effective C and N sinks management, providing valuable data for informed decision-making. For example, afforestation in drylands can lead to significant increases in soil C and N stocks. However, In the future, further warming may lead to large losses of soil C and N in drylands.