Advancing our understanding of novel nitrous oxide reducers

<p>Sources of N<sub>2</sub>O (nitrous oxide) are multiple in the biosphere, but the only known process consuming N<sub>2</sub>O is the microbial reduction of N<sub>2</sub>O to dinitrogen (N<sub>2</sub>), which has traditionally been attributed to denitrifying bacteria and archaea. Recently, N<sub>2</sub>O reductase genes (nosZ) clearly phylogenetically differentiated from “typical” NosZ (Clade I) were shown to be more abundant in many soil ecosystems than “typical” nosZ genes, suggesting that our understanding of the role of nosZ in controlling soil N<sub>2</sub>O emissions was incomplete. This more abundant group of nosZ genes was designated as “atypical NosZ” or Clade II.  Here, by synthesizing a meta-data of the 631 peer-reviewed papers published on NosZ in the six years since NosZ Clade II was first reported in the literature, we found that only 10% of studies evaluated Clade II NosZ and an additional 7% of papers merely mentioned Clade II NosZ showing little awareness of this novel gene. In addition, disciplinary silos also contribute to the slow spread of awareness about Clade II nosZ. A lack of consensus on the terminology used to refer to Clade I versus Clade II nosZ (more than 17 terminologies) may contribute to confusion about the two clades. Finally, we proposed several recommendations to accelerate progress in understanding the roles of Clade I versus Clade II N<sub>2</sub>O reducers in controlling soil N<sub>2</sub>O emissions.</p>