Abstract

Biochar amendment has been proven to generally reduce soil nitrous oxide (N2O) emissions. However, the effects and underlying mechanisms of biochar-derived reactive oxygen species (ROS) on soil N2O emissions are still unclear. Thus, we firstly weakened the intensities of persistent free radicals (PFRs) within biochar using triethanolamine (TEA) as a quencher, and then used soil incubation methods to compare the potentials of TEA-quenched and un-quenched biochar in mitigating soil N2O emissions. The TEA-quenched biochar generated less hydrogen peroxide (H2O2) and hydroxyl radical (•OH), while having a higher soil N2O emission mitigation potential, than the un-quenched biochar. The N2O emissions and the N2O/(N2O + N2) ratio were significantly, positively, correlated with the generated H2O2 and •OH contents. These results demonstrated that biochar-derived ROS weakened biochar's mitigation of soil N2O emissions. The specific mechanisms of biochar-derived ROS on soil N2O emissions were further explored by a ROS scavenging experiment. It was found that scavenging H2O2 by catalase efficiently hindered the generation of •OH, resulting in decreases in N2O emissions and the N2O/(N2O + N2) ratio. Meanwhile, biochar-derived ROS exhibited a more severe inhibition on N2O reductase gene (nosZ) expression than that on the expression of genes responsible for N2O production (nirK and nirS), indicating that biochar-derived ROS weakened biochar's mitigation of soil N2O emissions by inhibiting microbial N2O reduction. Our results imply that controlling the content of biochar-derived ROS is a promising strategy to maximize biochar's potential for mitigating soil N2O emission.

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