Effect of Woodchips Biochar on Sensitivity to Temperature of Soil Greenhouse Gases Emissions.

Research Highlights: Biochar is the carbonaceous product of pyrolysis or the gasification of biomass that is used as soil amendment to improve soil fertility and increase soil carbon stock. Biochar has been shown to increase, decrease, or have no effect on the emissions of greenhouse gases (GHG) from soil, depending on the specific soil and biochar characteristics. However, the temperature sensitivity of these gas emissions in biochar-amended soils is still poorly investigated. Background and Objectives: A pot experiment was set up to investigate the impact of woodchips biochar on the temperature sensitivity of the main GHG (CO₂, CH₄, and N₂O) emissions from soil. Materials and Methods: Nine pots (14 L volume) were filled with soil mixed with biochar at two application rates (0.021 kg of biochar/kg of soil and 0.042 kg of biochar/kg of soil) or with soil alone as the control (three pots per treatment). Pots were incubated in a growth chamber and the emissions of CO₂, CH₄, and N₂O were monitored for two weeks with a cavity ring-down gas analyzer connected to three closed dynamic chambers. The temperature in the chamber increased from 10 °C to 30 °C during the first week and decreased back to 10 °C during the second week, with a daily change of 5 °C. Soil water content was kept at 20% (w/w). Results: Biochar application did not significantly affect the temperature sensitivity of CO₂ and N₂O emissions. However, the sensitivity of CH₄ uptake from soil significantly decreased by the application of biochar, reducing the CH₄ soil consumption compared to the un-amended soil, especially at high soil temperatures. Basal CO₂ respiration at 10 °C was significantly higher in the highest biochar application rate compared to the control soil. Conclusions: These results confirmed that the magnitude and direction of the influence of biochar on temperature sensitivity of GHG emissions depend on the specific GHG considered. The biochar tested in this study did not affect soil N₂O emission and only marginally affected CO₂ emission in a wide range of soil temperatures. However, it showed a negative impact on soil CH₄ uptake, particularly at a high temperature, having important implications in a future warmer climate scenario and at higher application rates. [ABSTRACT FROM AUTHOR]