Biological nitrous oxide consumption in oxygenated waters of the high latitude Atlantic Ocean

Andrew P Rees,Amal Jayakumar,Gennadi Lessin,Ian J Brown,Paul J Somerfield,Bess B Ward

doi:10.1038/s43247-021-00104-y

Andrew P Rees, Amal Jayakumar + Show 4 more

Open Access

https://doi.org/10.1038/s43247-021-00104-y

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Abstract

Nitrous oxide (N2O) is important to the global radiative budget of the atmosphere and contributes to the depletion of stratospheric ozone. Globally the ocean represents a large net flux of N2O to the atmosphere but the direction of this flux varies regionally. Our understanding of N2O production and consumption processes in the ocean remains incomplete. Traditional understanding tells us that anaerobic denitrification, the reduction of NO3− to N2 with N2O as an intermediate step, is the sole biological means of reducing N2O, a process known to occur in anoxic environments only. Here we present experimental evidence of N2O removal under fully oxygenated conditions, coupled with observations of bacterial communities with novel, atypical gene sequences for N2O reduction. The focus of this work was on the high latitude Atlantic Ocean where we show bacterial consumption sufficient to account for oceanic N2O depletion and the occurrence of regional sinks for atmospheric N2O.

Highlights

Nitrous oxide (N2O) is important to the global radiative budget of the atmosphere and contributes to the depletion of stratospheric ozone
Constraining the magnitude of production and consumption processes is essential to understand how the biotic environment contributes to atmospheric concentrations[3]
Canonical understanding of the nitrogen cycle tells us that the only biological process that consumes N2O is the final stage of denitrification[5] where N2O is reduced to N2 under anoxic conditions by the enzyme nitrous oxide reductase (N2OR), encoded by the nosZ gene[6]

Summary

Introduction

Nitrous oxide (N2O) is important to the global radiative budget of the atmosphere and contributes to the depletion of stratospheric ozone. Traditional understanding tells us that anaerobic denitrification, the reduction of NO3− to N2 with N2O as an intermediate step, is the sole biological means of reducing N2O, a process known to occur in anoxic environments only. Constraining the magnitude of production and consumption processes is essential to understand how the biotic environment contributes to atmospheric concentrations[3]. Canonical understanding of the nitrogen cycle tells us that the only biological process that consumes N2O is the final stage of denitrification[5] where N2O is reduced to N2 under anoxic conditions by the enzyme nitrous oxide reductase (N2OR), encoded by the nosZ gene[6]. Whilst there are no reported observations of N2O consumption in oxygenated ocean waters, several authors have indicated the presence of microbial communities with the potential to reduce N2O21–26. Raes et al.[23] reported nosZ genes associated with Rhodobacteraceae in oxic waters of the south-eastern

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