Temperature sensitivity of biochar and native carbon mineralisation in biochar-amended soils

Abstract

Temperature sensitivity of biochar-C in soils is not well understood. To acquire this information, we incubated two δ13C-depleted (−36.3 or −36.5‰) 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 CO2 and associated δ13C were analysed periodically (12–22 times) over two years. The temperature sensitivity of biochar-C and native SOC mineralisation was computed as: (i) averaged Q10 (Q10a) for the whole (2-year) time series using a temperature-incorporated mineralisation model to estimate a temperature scaling function for the exponential Q10 model; (ii) instantaneous Q10 (Q10i) by using a time series of C mineralisation rates for a simple Q10 model; and (iii) cumulative Q10 (Q10c) by using cumulative C mineralised over certain incubation periods for a simple Q10 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 Q10a 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 Q10a were the smallest in the Vertisol for the 40–60°C range. Biochar-C Q10a was not influenced by biochar type (450 or 550°C). The presence of biochar decreased Q10a 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 (Q10a and Q10c) and SOC (Q10a and Q10i) decreased with increasing incubation temperature range. The Q10i 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 Q10a, Q10c and Q10i 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.