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

Abstract

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.