Soils release CO₂ to atmosphere through the mineralization of soil organic carbon (SOC) and this contributes to the increasing atmosphere CO2 concentration. Meanwhile, soils also sequestrate atmospheric CO₂ through organic material and plant root inputs. When the carbon input to soil is larger than the carbon output from soil, the soil will accumulate organic carbon, as well as sequestrate the atmospheric CO₂. Any measures to increase soil organic carbon favor the mitigation of atmospheric CO₂ concentration.

Paddy soils for rice cultivation are common land resources in subtropical and tropical regions, and are distinctive in their physical and biological conditions under artificial water logging. These unique soil conditions make the difference in the process of SOC mineralization from the upland soils, as well as the role of soil conditions (such as soil clay content). Recently, soil winter warming in subtropical and tropical regions are reported as a consequence of global climatic change. Such increasing soil temperature may influence SOC mineralization and the relative role of soil conditions.

Using field sampling and laboratory incubation, a team of researchers from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) explore the dynamics of SOC mineralization, and the relative effect of temperature and clay content for subtropical paddy soils.

The researchers found that CO₂ evolution through SOC mineralization during the incubation followed the order of clay loam > silty clay > sand loam. The temperature response coefficients (Q10) followed the order of clay loam (2.36) > sand loam (1.92) > silty clay (2.10). The soil clay content followed the order of silty clay > clay loam > sand loam. Even though the sand loam has lower contents of soil clay, its SOC mineralization and Q10 were not higher than the other two soils. It seems that soil clay content was not a control factor of SOC mineralization.

The researchers also found that the size of active soil C pool increased with increasing temperature. The silty clay soil had the smallest active C pool (1.40%) and the largest Q10 value (6.33) in the active C pool as compared with the other two soils. SOC mineralization and its temperature response in subtropical paddy soils was probably dominantly controlled by the substrate availability and the specific stabilization mechanisms of SOC.

The research was supported by "the Strategic Priority Research Program — Climate Change: Carbon Budget and Related Issues" of the Chinese Academy of Sciences (grant no. XDA05050505), the Natural Science Foundation of China (grants no. 41090283, 41001141), and the International S&T cooperation program of China (grant no. 2011DFA30770)

The study entitled “Organic carbon mineralization responses to temperature increases in subtropical paddy soils” has been published in Volume 14, Januarly 2014 of Journal of soils and sediments, details could be found at http://link.springer.com/article/10.1007%2Fs11368-013-0781-4