A Critical Review on Nitrous Oxide Production by Ammonia-Oxidizing Archaea

The continuous increase of nitrous oxide (N 2 O) in the atmosphere has become a global concern because of its property as a potent greenhouse gas. Given the important role of ammonia-oxidizing archaea (AOA) in ammonia oxidation and their involvement in N 2 O production, a clear understanding of the knowledge on archaeal N 2 O production is necessary for global N 2 O mitigation. Compared to bacterial N 2 O production by ammonia-oxidizing bacteria (AOB), AOA-driven N 2 O production pathways are less-well elucidated. In this Critical Review, we synthesized the currently proposed AOA-driven N 2 O production pathways in combination with enzymology distinction, analyzed the role of AOA species involved in N 2 O production pathways, discussed the relative contribution of AOA to N 2 O production in both natural and anthropogenic environments, summarized the factors affecting archaeal N 2 O yield, and compared the distinctions among approaches used to differentiate ammonia oxidizer-associated N 2 O production. We, then, put forward perspectives for archaeal N 2 O production and future challenges to further improve our understanding of the production pathways, putative enzymes involved and potential approaches for identification in order to potentially achieve effective N 2 O mitigations.