Impact of desertification and global warming on soil carbon in northern China

Abstract

While the global rise in mean day/night and seasonal air temperatures (ATE) of recent decades is well documented, its influence on levels of soil‐sequestered organic carbon, and on emission rates of CO2 and other greenhouse gases emanating therefrom, is only beginning to garner serious attention. This has resulted in a limited but growing understanding, particularly in the context of the lands of the Chinese subcontinent, of the mechanisms underlying such emissions. Some 340 soil samples from 12 different sandy land regions in China were analyzed for soil organic carbon (SOC) content. Stepwise regression identified correlations between SOC and a number of climatic factors measured at the sampling sites: winter, summer, nighttime and daytime ATE, and precipitation. In desertified lands, net SOC losses showed a direct correlation with precipitation but no significant relationship with mean ATE. However, in northwest and northeast China, decreases in SOC were linked to rises in day/night and seasonal ATE, while in north central China they were linked to a rise in mean ATE. Between 1900 and 1998, mean ATE in the northwest, northeast, and north central regions rose by 0.14E, 0.28E, and 0.15E decade−1, respectively. Meanwhile, precipitation dropped by 25 mm decade−1 across these regions. In this study, day/night and seasonal ATE showed differing levels of significance with respect to their linear relationships with SOC content. Driven by rises in day/night and seasonal ATE, long‐term alterations to global ecosystemic processes, particularly the carbon cycle, may quantitatively and qualitatively alter the flora of desertified ecosystems. Our study suggests that, over the last 40 years, anthropogenic factors, precipitation, and rises in ATE (particularly nighttime and winter) have contributed 47%, 26%, and 20%, respectively, of greenhouse gas emissions from SOC. It is apparent that for China's desertified lands, human activity is the primary causative factor in the release of SOC‐derived greenhouse gases to the atmosphere, while geography and climatic extremes individually play a lesser role.