Modeling the impact of climate change on soil organic carbon stock in upland soils in the 21st century in China

Soil organic carbon (SOC) is an important carbon pool which can ameliorate the increasing concentration of atmospheric carbon dioxide as part of the carbon cycling process. Organic carbon in cropland soils is an active pool which is strongly influenced by anthropogenic activities. SOC in cropland soils accounted for 14.5% of the total organic carbon stock of 89.61 Mt C in China. In this study, RothC model was used to simulate the change of SOC in upland soils at 626 original 50 km × 50 km grids under B2 and A2 climate scenarios during the upcoming decades in China. Future climate data under B2 and A2 scenarios were predicted by Providing Regional Climates for Impacts Studies (PRECIS) regional climate model downscaled based on HadCM3. The simulation results showed that SOC will generally decrease during the next decades and the decrease rate of SOC will be higher over time if there is no addition of organic material (e.g. organic manure application or straw return) adopted in China. Simulations got the following results: (i) SOC will decrease in most areas of China, especially in northern China; the increase of SOC only occurred in a few scattered grids in Southwest China and mid-south China. The decrease rate of SOC in northern China was higher than in southern China under either B2 or A2 climate scenarios. (ii) The changing rate of SOC over time under B2 scenario was minor during the early 21st century and quite large during the late 21st century. In contrast, the changing rate of SOC over time under A2 scenario was somewhat constant over time. The percentage decrease (decrease rate divided by its basic value in 1980s) of SOC in northern China was around 5.5%, 12%, and 15% by the year 2020, 2050, and 2080 under B2 and A2 scenarios, while it was about 2.3%, 7.7%, and 10.9% under B2 scenario and 3.3%, 4.5%, and 5.5% under A2 scenario in southern China. (iii) Upland soils would lose organic carbon by 2.7 t C/ha, 6.0 t C/ha, and 7.8 t C/ha at the 0–30 cm depth by the year 2020, 2050, and 2080, respectively, under the typical conventional tillage without organic material amendment under B2 scenario in China, which accounted for about 4.2%, 9.3%, and 12.1%, respectively, of the basic SOC of 1980s in the upland soils. SOC would decrease by 2.9 t C/ha, 6.8 t C/ha, and 8.2 t C/ha by the year 2020, 2050, and 2080, respectively, under A2 scenario in China, which accounted for about 4.5%, 10.5%, and 12.7%, respectively, of that in 1980s under the conventional tillage and management practices. (iv) Our simulations of future change in SOC suggest it is the influence of combination by temperature, precipitation, evaporation, and original soil properties together and that the predominant factors and the interaction among these factors will vary in different geographical regions. The limitations and uncertainties of the simulation are also discussed.