Direct biological fixation provides a freshwater sink for N2O

Si, Yueyue; Zhu, Yizhu; Sanders, Ian; Kinkel, Dorothee B.; Purdy, Kevin J.; Trimmer, Mark

doi:10.1038/s41467-023-42481-2

Cited by 8 publications

(1 citation statement)

References 76 publications

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“…N2O consumption via denitrification is more sensitive to oxygen than N2O production via denitrification (Farías et al 2009;Dalsgaard et al 2014;Babbin et al 2015;Frey et al 2020), although the oxygen inhibition constant for N2O consumption remains difficult to define (Sun et al 2021b). N2O may also be consumed through N2O fixation, although the importance of N2O fixation in the ocean has yet to be determined (Farías et al 2013;Si et al 2023).…”

Section: Introductionmentioning

confidence: 99%

Isotopomer labeling and oxygen dependence of hybrid nitrous oxide production

Kelly,

Travis,

Baya

et al. 2023

Preprint

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Abstract. Nitrous oxide (N2O) is a potent greenhouse gas and ozone depletion agent, with a significant natural source from marine oxygen deficient zones (ODZs). Open questions remain, however, about the microbial processes responsible for this N2O production, especially hybrid N2O production when ammonia-oxidizing archaea are present. Using 15N-labeled tracer incubations, we measured the rates of N2O production from ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-) in the Eastern Tropical North Pacific ODZ, as well as the isotopic labeling of the central (α) and terminal (β) nitrogen atoms of the N2O molecule. We observed production of both doubly- and singly labeled N2O from each tracer, with the highest rates of labeled N2O production at the same depths as the near-surface N2O concentration maximum. At most stations and depths, the production of 45N2Oα and 45N2Oβ were statistically indistinguishable, but at a few depths, there were significant differences in the labelling of the two nitrogen atoms in the N2o molecule. Implementing the rates of labeled N2O production in a forward-running model, we found that N2O production from NO3- dominated at most stations and depths, with rates as high as 1.6±0.2 nM N2O/day. Hybrid N2O production, one of the mechanisms by which ammonia-oxidizing archaea produce N2O, had rates as high as 0.23±0.08 nM N2O/day that peaked in both the near-surface and deep N2O concentration maxima. We inferred from the 45N2Oα and 45N2Oβ data that hybrid N2O production by ammonia-oxidizing archaea may have a variable site preference that depends on the 15N content of each substrate. We also found that the rates and yields of hybrid N2O production exhibited a clear [O2] inhibition curve, with the hybrid N2O yields as high as 20 % at depths where dissolved [O2] was 0 µM but nitrification was still active. Finally, we identified a few incubations with dissolved [O2] up to 20 µM where N2O production from NO3- was still active. A relatively high O2 tolerance for N2O production via denitrification has implications for the feedbacks between marine deoxygenation and greenhouse gas cycling.

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Section: Introductionmentioning

confidence: 99%

Isotopomer labeling and oxygen dependence of hybrid nitrous oxide production

Kelly,

Travis,

Baya

et al. 2023

Preprint

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Nutrient enrichment—but not warming—increases nitrous oxide emissions from shallow lake mesocosms

Audet,

Levi,

Jeppesen

et al. 2024

Limnology & Oceanography

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Shallow lakes and ponds play a crucial role in the processing of carbon and other nutrients. However, many lakes and ponds worldwide are affected by climate change and nutrient pollution. How these pressures affect the emission of the greenhouse gas nitrous oxide (N2O) is unclear. Warming and eutrophication are expected to increase the production and emission of N2O in lakes and ponds, but changes in ecological structure and function may complicate these seemingly straightforward relationships. In this study, we used the world's longest running, mesocosm‐based, freshwater climate change experiment to disentangle the effect of nutrient enrichment and warming on N2O emissions. We gathered a large dataset on N2O concentrations and ancillary variables, comprising three sampling campaigns between 2011 and 2020 and a total of 687 individual mesocosm measurements. Our results demonstrated that nutrient enrichment increased N2O emissions, while warming (+2.5–4.0°C and +3.75–6.0°C) had no discernable effect. Our study indicates that curtailing nitrogen influxes into lakes and ponds is the most effective strategy to minimize N2O emissions, and while warming may influence N2O emissions, it does not appear to be a direct driver. These findings underscore the importance of prioritizing nitrogen mitigation efforts to curb N2O emissions from shallow lakes and ponds.

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