Quantification of the soil organic carbon balance in the Tai-Lake paddy soils of China

Rising temperatures and elevated atmospheric CO2 are two factors that simultaneously affect the dynamics of soil organic carbon (SOC). This study separately examines the effects arise from these two factors in Tai-Lake Paddy soils using DeNitrification–DeComposition (DNDC) model, with the currently most detailed soil database for the paddy region of China. The soil database is at a scale of 1:50,000, containing 52,034 paddy soil polygons derived from 1107 unique paddy soil profiles. Our simulations indicate that, the SOC in the top soils (0-30 cm) increases 0.83, 1.09, 1.32, and 1.51 Tg C under conventional management (3.44 Tg C) in the 2.32 Mha paddy soils of the Tai-Lake region from 2001 to 2019, respectively, with the atmospheric CO2 concentration increases at 1.5, 2.0, 2.5, and 3.0 times the normal rate (1.9 ppm year−1). By contrast, with rising air temperature of 0.5, 1.0, 1.5, 2.0, 3.0, and 4 °C, the SOC decreases 0.09, 0.54, 0.69, 1.13, 1.80, and 2.51 Tg C under conventional management, respectively. Thus, the effect of carbon sink induced from CO2 fertilization at the 2.0 times normal CO2 concentration increase rate could generally offset the effect of carbon source resulted from a 2.0 °C air temperature increase. In addition, the paddy soils in this region tend to persistently be a sink of atmospheric CO2 under warming and elevated CO2 scenarios, even if when the air temperature has increased by 4 °C. These results suggest that SOC storage in paddy soils of this region is prone to benefit from future global climate change and this carbon sequestration potential in the agro-ecosystems is likely to contribute to climate mitigation under current agricultural practices, despite any negative effects derived from warming. As a representative of paddy soils in eastern China, the insights gained from the Tai-Lake region may be potentially transferable to other paddy soils in eastern China where 95% of the total of China is located.