Biochar as electron donor for reduction of N(2)O by Paracoccus denitrificans

Biochar (BC) has been shown to influence microbial denitrification and mitigate soil N(2)O emissions. However, it is unclear if BC is able to directly stimulate the microbial reduction of N(2)O to N(2). We hypothesized that the ability of BC to lower N(2)O emissions could be related not only to its ability to store electrons, but to donate them to bacteria that enzymatically reduce N(2)O. Therefore, we carried out anoxic incubations with Paracoccus denitrificans, known amounts of N(2)O, and nine contrasting BCs, in the absence of any other electron donor or acceptor. We found a strong and direct correlation between the extent and rates of N(2)O reduction with BC's EDC/EEC (electron donating capacity/electron exchange capacity). Apart from the redox capacity, other BC properties were found to regulate the BC's ability to increase N(2)O reduction by P. denitrificans. For this specific BC series, we found that a high H/C and ash content, low surface area and poor lignin feedstocks favored N(2)O reduction. This provides valuable information for producing tailored BCs with the potential to assist and promote the reduction of N(2)O in the pursuit of reducing this greenhouse gas emissions.