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Oxygen sensitivity of anammox and coupled N-cycle processes in oxygen minimum zones

Oxygen sensitivity of anammox and coupled N-cycle processes in oxygen minimum zones
Oxygen sensitivity of anammox and coupled N-cycle processes in oxygen minimum zones
Nutrient measurements indicate that 30–50% of the total nitrogen (N) loss in the ocean occurs in oxygen minimum zones (OMZs). This pelagic N-removal takes place within only ~0.1% of the ocean volume, hence moderate variations in the extent of OMZs due to global warming may have a large impact on the global N-cycle. We examined the effect of oxygen (O2) on anammox, NH3 oxidation and NO3? reduction in 15N-labeling experiments with varying O2 concentrations (0–25 µmol L?1) in the Namibian and Peruvian OMZs. Our results show that O2 is a major controlling factor for anammox activity in OMZ waters. Based on our O2 assays we estimate the upper limit for anammox to be ~20 µmol L?1. In contrast, NH3 oxidation to NO2? and NO3? reduction to NO2? as the main NH4+ and NO2? sources for anammox were only moderately affected by changing O2 concentrations. Intriguingly, aerobic NH3 oxidation was active at non-detectable concentrations of O2, while anaerobic NO3? reduction was fully active up to at least 25 µmol L?1 O2. Hence, aerobic and anaerobic N-cycle pathways in OMZs can co-occur over a larger range of O2 concentrations than previously assumed. The zone where N-loss can occur is primarily controlled by the O2-sensitivity of anammox itself, and not by any effects of O2 on the tightly coupled pathways of aerobic NH3 oxidation and NO3? reduction. With anammox bacteria in the marine environment being active at O2 levels ~20 times higher than those known to inhibit their cultured counterparts, the oceanic volume potentially acting as a N-sink increases tenfold. The predicted expansion of OMZs may enlarge this volume even further. Our study provides the first robust estimates of O2 sensitivities for processes directly and indirectly connected with N-loss. These are essential to assess the effects of ocean de-oxygenation on oceanic N-cycling.
1932-6203
e29299
Kalvelage, Tim
216fac21-892d-46d7-995d-5e959962bc06
Jensen, Marlene M.
23ff1ce5-4644-4816-be78-4762c15266e0
Contreras, Sergio
7faae1cd-7a96-4023-9996-f6b19ea6627c
Revsbech, Niels Peter
38ea27cf-f8cf-4943-bf6c-7698528da7de
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
Günter, Marcel
d6dbe6e7-8d4e-469a-a77b-cb567a71d44d
LaRoche, Julie
21d1685a-3dbd-4ccd-9ae4-e968c8792297
Lavik, Gaute
29014780-d97c-41c0-8b59-a230bdfcdb37
Kuypers, Marcel M.M.
b6288cfb-42bc-469c-93fe-8fbb40d97bec
Kalvelage, Tim
216fac21-892d-46d7-995d-5e959962bc06
Jensen, Marlene M.
23ff1ce5-4644-4816-be78-4762c15266e0
Contreras, Sergio
7faae1cd-7a96-4023-9996-f6b19ea6627c
Revsbech, Niels Peter
38ea27cf-f8cf-4943-bf6c-7698528da7de
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
Günter, Marcel
d6dbe6e7-8d4e-469a-a77b-cb567a71d44d
LaRoche, Julie
21d1685a-3dbd-4ccd-9ae4-e968c8792297
Lavik, Gaute
29014780-d97c-41c0-8b59-a230bdfcdb37
Kuypers, Marcel M.M.
b6288cfb-42bc-469c-93fe-8fbb40d97bec

Kalvelage, Tim, Jensen, Marlene M., Contreras, Sergio, Revsbech, Niels Peter, Lam, Phyllis, Günter, Marcel, LaRoche, Julie, Lavik, Gaute and Kuypers, Marcel M.M. (2011) Oxygen sensitivity of anammox and coupled N-cycle processes in oxygen minimum zones. PLoS ONE, 6 (12), e29299. (doi:10.1371/journal.pone.0029299).

Record type: Article

Abstract

Nutrient measurements indicate that 30–50% of the total nitrogen (N) loss in the ocean occurs in oxygen minimum zones (OMZs). This pelagic N-removal takes place within only ~0.1% of the ocean volume, hence moderate variations in the extent of OMZs due to global warming may have a large impact on the global N-cycle. We examined the effect of oxygen (O2) on anammox, NH3 oxidation and NO3? reduction in 15N-labeling experiments with varying O2 concentrations (0–25 µmol L?1) in the Namibian and Peruvian OMZs. Our results show that O2 is a major controlling factor for anammox activity in OMZ waters. Based on our O2 assays we estimate the upper limit for anammox to be ~20 µmol L?1. In contrast, NH3 oxidation to NO2? and NO3? reduction to NO2? as the main NH4+ and NO2? sources for anammox were only moderately affected by changing O2 concentrations. Intriguingly, aerobic NH3 oxidation was active at non-detectable concentrations of O2, while anaerobic NO3? reduction was fully active up to at least 25 µmol L?1 O2. Hence, aerobic and anaerobic N-cycle pathways in OMZs can co-occur over a larger range of O2 concentrations than previously assumed. The zone where N-loss can occur is primarily controlled by the O2-sensitivity of anammox itself, and not by any effects of O2 on the tightly coupled pathways of aerobic NH3 oxidation and NO3? reduction. With anammox bacteria in the marine environment being active at O2 levels ~20 times higher than those known to inhibit their cultured counterparts, the oceanic volume potentially acting as a N-sink increases tenfold. The predicted expansion of OMZs may enlarge this volume even further. Our study provides the first robust estimates of O2 sensitivities for processes directly and indirectly connected with N-loss. These are essential to assess the effects of ocean de-oxygenation on oceanic N-cycling.

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Published date: 28 December 2011
Organisations: Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 349915
URI: https://eprints.soton.ac.uk/id/eprint/349915
ISSN: 1932-6203
PURE UUID: d22955b7-6611-46fc-a250-65e8339ae268
ORCID for Phyllis Lam: ORCID iD orcid.org/0000-0003-2067-171X

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Date deposited: 13 Mar 2013 13:50
Last modified: 10 Dec 2019 01:35

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