Biochar as electron donor for reduction of N2O by Paracoccus denitrificans.

Biochar has been shown to influence microbial denitrification and mitigate soil N2O emissions. However, it is unclear if biochar is able to directly stimulate the microbial reduction of N2O to N2. We hypothesized that the ability of biochar to lower N2O emissions could be related not only to its ability to store electrons, but to donate them to bacteria that enzymatically reduce N2O. Therefore, we carried out anoxic incubations with Paracoccus denitrificans, known amounts of N2O, and nine contrasting biochars, in the absence of any other electron donor or acceptor. We found a strong and direct correlation between the extent and rates of N2O reduction with biochar's EDC/EEC (electron donating capacity/electron exchange capacity). Apart from the redox capacity, other biochar properties were found to regulate the biochar; s ability to increase N2O reduction by Paracoccus denitrificans. For this specific biochar series, we found that a high H/C and ash content, low surface area and poor lignin feedstocks favoured N2O reduction. This provides valuable information for producing tailored biochars with the potential to assist and promote the reduction of N2O in the pursuit of reducing this greenhouse gas emissions.