Advanced

Aerobic and anaerobic nitrogen transformation processes in N-2-fixing cyanobacterial aggregates

Klawonn, Isabell; Bonaglia, Stefano LU ; Bruchert, Volker and Ploug, Helle (2015) In The Isme Journal 9(6). p.1456-1466
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. N-15-isotope labelling experiments and nutrient analyses revealed that N-2 fixation, ammonification, nitrification, nitrate reduction to ammonium, denitrification and possibly anaerobic ammonium... (More)
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. N-15-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 lowoxygenated waters (<= 25 mu M). We propose that the net effect of aggregates on nitrogen loss is negligible in NO3--depleted, fully oxygenated (surface) waters. In NO3--enriched (>1.5 mu M), 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. (Less)
Please use this url to cite or link to this publication:
author
publishing date
type
Contribution to journal
publication status
published
subject
in
The Isme Journal
volume
9
issue
6
pages
1456 - 1466
publisher
Nature Publishing Group
external identifiers
  • wos:000354786700016
  • scopus:84929656119
ISSN
1751-7362
DOI
10.1038/ismej.2014.232
language
English
LU publication?
no
id
02656293-378a-4064-8ca5-b5676e8029f0 (old id 8522751)
date added to LUP
2016-01-18 17:07:42
date last changed
2017-11-12 03:12:42
@article{02656293-378a-4064-8ca5-b5676e8029f0,
  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. N-15-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 (&gt;= 1 mm) even when suspended in fully oxygenated waters, whereas anoxia in small aggregates (&lt;1 to &gt;= 0.1 mm) may only arise in lowoxygenated waters (&lt;= 25 mu M). We propose that the net effect of aggregates on nitrogen loss is negligible in NO3--depleted, fully oxygenated (surface) waters. In NO3--enriched (&gt;1.5 mu M), 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.},
  author       = {Klawonn, Isabell and Bonaglia, Stefano and Bruchert, Volker and Ploug, Helle},
  issn         = {1751-7362},
  language     = {eng},
  number       = {6},
  pages        = {1456--1466},
  publisher    = {Nature Publishing Group},
  series       = {The Isme Journal},
  title        = {Aerobic and anaerobic nitrogen transformation processes in N-2-fixing cyanobacterial aggregates},
  url          = {http://dx.doi.org/10.1038/ismej.2014.232},
  volume       = {9},
  year         = {2015},
}