Biochar's role as an electron shuttle for mediating soil N2O emissions

The functionality of biochar as an electron shuttle has been hypothesized to rationalize its suppressing effect on nitrous oxide (N2O) emissions from soil denitrification. However, this hypothesis has not yet been experimentally confirmed in soil matrices. In this study, we weakened biochar's function as an electron shuttle using a hydrogen peroxide pretreatment. Biochar addition supressed soil N2O emissions compare to a nil biochar control, but oxidized biochar increased soil N2O emission rates and N2O/(N2O + N2) emission ratio. The increasing extent of the soil N2O emission rate significantly correlated positively with the abundance of the biochar's oxidative moieties (e.g., C=O groups). These results imply that addition of biochar with a strong electron shuttle function will decrease soil N2O emissions whereas biochar aging will weaken or even reverse the suppressing effects on soil N2O emissions.