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N 2 -fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community

The ISME Journal, 2016-02, Vol.10 (2), p.450 [Peer Reviewed Journal]

ISSN: 1751-7370 ;ISSN: 1751-7362 ;EISSN: 1751-7370 ;DOI: 10.1038/ismej.2015.126

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  • Title:
    N 2 -fixation, ammonium release and N-transfer to the microbial and classical food web within a plankton community
  • Author: Adam, Birgit ; Klawonn, Isabell ; Svedén, Jenny B. ; Bergkvist, Johanna ; Nahar, Nurun ; Walve, Jakob ; Littmann, Sten ; Whitehouse, Martin J. ; Lavik, Gaute ; Kuypers, Marcel M. M. ; Ploug, Helle
  • Subjects: marin ekologi ; Marine Ecology
  • Is Part Of: The ISME Journal, 2016-02, Vol.10 (2), p.450
  • Description: We investigated the role of N 2 -fixation by the colony-forming cyanobacterium,  Aphanizomenon  spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with  15 N 2 ,  Aphanizomenon  spp. showed a strong  15 N-enrichment implying substantial  15 N 2 -fixation. Intriguingly,  Aphanizomenon  did not assimilate tracers of  15 NH 4 +  from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH 4 +  fluxes to  Aphanizomenon  colonies at low bulk concentrations (<250 nm) as compared with N 2 -fixation within colonies. No N 2 -fixation was detected in autotrophic microorganisms <5 μm, which relied on NH 4 + uptake from the surrounding water.  Aphanizomenon  released about 50% of its newly fixed N 2  as NH 4 + . However, NH 4 +  did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms ( Chaetoceros  sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon  releases about half of its recently fixed N 2  as NH 4 + , which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N 2 -fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.
  • Language: English
  • Identifier: ISSN: 1751-7370
    ISSN: 1751-7362
    EISSN: 1751-7370
    DOI: 10.1038/ismej.2015.126
  • Source: PubMed Central
    ProQuest Central
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