Temperature sensitivity of biochar-C in soils is not well understood. To acquire this information, we incubated two delta 13C-depleted (-36.3 or -36.5 per mil) wood biochars produced at 450 and 550°C, under controlled laboratory conditions at 20, 40 and 60°C in four contrasting soils (Inceptisol, Entisol, Oxisol and Vertisol). The respired CO 2 and associated delta 13C were analysed periodically (12-22 times) over two years. The temperature sensitivity of biochar-C and native SOC mineralisation was computed as: (i) averaged Q 10 (Q 10a) for the whole (2-year) time series using a temperature-incorporated mineralisation model to estimate a temperature scaling function for the exponential Q 10 model; (ii) instantaneous Q 10 (Q 10i) by using a time series of C mineralisation rates for a simple Q 10 model; and (iii) cumulative Q 10 (Q 10c) by using cumulative C mineralised over certain incubation periods for a simple Q 10 model. The mineralisation rates of biochar-C and native SOC increased with increasing temperature and their temperature sensitivities were significantly ( p<0.001) affected by soil type. For example, biochar-C Q 10a was the greatest (also for native SOC) in the Vertisol (2.74-2.77), followed by Inceptisol (2.47-2.66) and Entisol (2.39-2.45), and the smallest in the Oxisol (1.93-2.20) for the 20-40°C range. Biochar and native SOC Q 10a were the smallest in the Vertisol for the 40-60°C range. Biochar-C Q 10a was not influenced by biochar type (450 or 550°C). The presence of biochar decreased Q 10a of the native SOC in the Entisol, Vertisol and Inceptisol, but this influence did not occur in the Oxisol, especially at 20-40°C. The temperature sensitivity of biochar-C (Q 10a and Q 10c) and SOC (Q 10a and Q 10i) decreased with increasing incubation temperature range. The Q 10i values of biochar-C and SOC increased with time in the 20-40°C range. Even though biochar-C was found to be more stable than native SOC (based on their mineralisation rate constants), the Q 10a, Q 10c and Q 10i values for biochar-C were either smaller or similar to that of native SOC. In conclusion, the findings of this study which was conducted in the absence of plant suggest that soil characteristics can alter the temperature sensitivity of biochar-C. Furthermore, biochar can decrease the temperature sensitivity of native SOC mineralisation and consequently enhance C sequestration in soil under climate warming.
