Temperature and moisture driven changes in soil carbon sequestration and mineralization under biochar addition

Sequestering more carbon in soil is an effective approach to mitigate climate change. The temporal variability of soil organic carbon (SOC) that reflects its loss and accumulation potential is important to model SOC sequestration under climate change, but it is still poorly understood under biochar addition. To identify the temporal variability of SOC, induced by climate conditions (i.e. precipitation and temperature) under biochar addition, a field experiment with the biochar addition rates of 0 (CK), 1.8 (BL), 3.6 (BM), and 7.2 (BH) mega gram (Mg) ha(-1) yr(-1) and a laboratory incubation under controlled conditions at 20, 40, and 70% moisture under 10 and 20 degrees C in CK and BH soils was conducted. The results showed that biochar addition increased average annual SOC sequestration rates by 31.8-47.8% (369.8-556.6 kg ha(-1) yr(-1)), and led to higher stock compared with CK. However, the annual sequestration rates of biochar addition showed a decreasing trend from 2014 (0.8-4.0 Mg ha(-1) yr(-1)) to 2018 (-7.1 to -3.5 Mg ha(-1) yr(-1)), and BH had the lowest sequestration rate from 2017 to 2018 compared with CK. Because the coefficients of variation of SOC concentration under biochar addition (1.2-11.0%) were significantly higher than those of CK (0.8-2.9%), indicating that biochar enhanced the temporal variability of SOC. The incubation study also confirmed that higher temporal variability under biochar addition resulted from increased sensitivity of SOC mineralization to temperature at 0-10 cm and to moisture at 10-20 cm layer. The high temporal variability was not conducive to the rates of carbon inputs retention in soil, and BH decreased by 20.4% compared with CK. Therefore, higher temporal variability induced by biochar addition constrains the potential for SOC sequestration, and middle and low rates (1.8-3.6 Mg ha(-1) yr(-1)) of biochar addition are promising and cost-effective options in the North China Plain.