Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates

Isabell Klawonn*, Stefano Bonaglia, Volker Brüchert, Helle Ploug

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Resumé

Colonies of N 2 -fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. 15 N-isotope labelling experiments and nutrient analyses revealed that N 2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N 2 were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (≥1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ≥0.1 mm) may only arise in low-oxygenated waters (≤25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO 3 - -depleted, fully oxygenated (surface) waters. In NO 3 - -enriched (>1.5 μM), O 2 -depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes.

OriginalsprogEngelsk
TidsskriftISME Journal
Vol/bind9
Udgave nummer6
Sider (fra-til)1456-1466
Antal sider11
ISSN1751-7362
DOI
StatusUdgivet - 23. jun. 2015
Udgivet eksterntJa

Fingeraftryk

Nitrogen
Ammonium Compounds
Nodularia spumigena
nitrogen
nitrate reduction
Recycling
nitrification
recycling
ammonium
nitrate
Isotope Labeling
ammonification
Snow
isotope labeling
Nitrous Oxide
Microelectrodes
mesopelagic zone
marine snow
nitrous oxide
Baltic Sea

Citer dette

Klawonn, Isabell ; Bonaglia, Stefano ; Brüchert, Volker ; Ploug, Helle. / Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates. I: ISME Journal. 2015 ; Bind 9, Nr. 6. s. 1456-1466.
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abstract = "Colonies of N 2 -fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. 15 N-isotope labelling experiments and nutrient analyses revealed that N 2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N 2 were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (≥1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ≥0.1 mm) may only arise in low-oxygenated waters (≤25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO 3 - -depleted, fully oxygenated (surface) waters. In NO 3 - -enriched (>1.5 μM), O 2 -depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes.",
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Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates. / Klawonn, Isabell; Bonaglia, Stefano; Brüchert, Volker; Ploug, Helle.

I: ISME Journal, Bind 9, Nr. 6, 23.06.2015, s. 1456-1466.

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

TY - JOUR

T1 - Aerobic and anaerobic nitrogen transformation processes in N2-fixing cyanobacterial aggregates

AU - Klawonn, Isabell

AU - Bonaglia, Stefano

AU - Brüchert, Volker

AU - Ploug, Helle

PY - 2015/6/23

Y1 - 2015/6/23

N2 - Colonies of N 2 -fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. 15 N-isotope labelling experiments and nutrient analyses revealed that N 2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N 2 were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (≥1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ≥0.1 mm) may only arise in low-oxygenated waters (≤25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO 3 - -depleted, fully oxygenated (surface) waters. In NO 3 - -enriched (>1.5 μM), O 2 -depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes.

AB - Colonies of N 2 -fixing cyanobacteria are key players in supplying new nitrogen to the ocean, but the biological fate of this fixed nitrogen remains poorly constrained. Here, we report on aerobic and anaerobic microbial nitrogen transformation processes that co-occur within millimetre-sized cyanobacterial aggregates (Nodularia spumigena) collected in aerated surface waters in the Baltic Sea. Microelectrode profiles showed steep oxygen gradients inside the aggregates and the potential for nitrous oxide production in the aggregates' anoxic centres. 15 N-isotope labelling experiments and nutrient analyses revealed that N 2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium oxidation (anammox) can co-occur within these consortia. Thus, N. spumigena aggregates are potential sites of nitrogen gain, recycling and loss. Rates of nitrate reduction to ammonium and N 2 were limited by low internal nitrification rates and low concentrations of nitrate in the ambient water. Presumably, patterns of N-transformation processes similar to those observed in this study arise also in other phytoplankton colonies, marine snow and fecal pellets. Anoxic microniches, as a pre-condition for anaerobic nitrogen transformations, may occur within large aggregates (≥1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (<1 to ≥0.1 mm) may only arise in low-oxygenated waters (≤25 μM). We propose that the net effect of aggregates on nitrogen loss is negligible in NO 3 - -depleted, fully oxygenated (surface) waters. In NO 3 - -enriched (>1.5 μM), O 2 -depleted water layers, for example, in the chemocline of the Baltic Sea or the oceanic mesopelagic zone, aggregates may promote N-recycling and -loss processes.

U2 - 10.1038/ismej.2014.232

DO - 10.1038/ismej.2014.232

M3 - Journal article

VL - 9

SP - 1456

EP - 1466

JO - I S M E Journal

JF - I S M E Journal

SN - 1751-7362

IS - 6

ER -