Temperature sensitivity of soil organic matter decomposition varies with biochar application and soil type

Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide (CO₂) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar (0, 6.25, 12.5, and 25 Mg ha⁻¹) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40°C. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO₂ emissions when compared to untreated soils; ii) CO₂ emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils; iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils; and iv) for clay soils, relative increases in soil CO₂ emissions from biochar-amended soils were higher when the temperature increased from 30 to 40 °C, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30 °C. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil- and weather-specific timing of biochar application.