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Competition for inorganic and organic forms of nitrogen and phosphorous between phytoplankton and bacteria during an Emiliania huxleyi spring bloom
Lovdal, T.; Eichner, C.; Grossart, H.; Carbonnel, V.; Chou, L.; Martin-Jezequel, V.; Thingstad, T. (2008). Competition for inorganic and organic forms of nitrogen and phosphorous between phytoplankton and bacteria during an Emiliania huxleyi spring bloom. Biogeosciences 5(2): 371-383. hdl.handle.net/10.5194/bg-5-371-2008
In: Gattuso, J.P.; Kesselmeier, J. (Ed.) Biogeosciences. Copernicus Publications: Göttingen. ISSN 1726-4170, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Lovdal, T.
  • Eichner, C.
  • Grossart, H.
  • Carbonnel, V., more
  • Chou, L., more
  • Martin-Jezequel, V.
  • Thingstad, T.

Abstract
    Using 15N and 33P, we measured the turnover of organic and inorganic nitrogen (N) and phosphorus (P) substrates, and the partitioning of N and P from these sources into two size fractions of marine osmotrophs during the course of a phytoplankton bloom in a nutrient manipulated mesocosm. The larger size fraction (>0.8 µm), mainly consisting of the coccolithophorid Emiliania huxleyi, but also including an increasing amount of large particle-associated bacteria as the bloom proceeded, dominated uptake of the inorganic forms NH4+, NO3-, and PO43-. The uptake of N from leucine, and P from ATP and dissolved DNA, was initially dominated by the 0.8–0.2 µm size fraction, but shifted towards dominance by the >0.8 µm size fraction as the system turned to an increasing degree of N-deficiency. Normalizing uptake to biomass of phytoplankton and heterotrophic bacteria revealed that organisms in the 0.8–0.2 µm size fraction had higher specific affinity for leucine-N than those in the >0.8 µm size fraction when N was deficient, whereas the opposite was the case for NH4+. There was no such difference regarding the specific affinity for P substrates. Since heterotrophic bacteria seem to acquire N from organic compounds like leucine more efficiently than phytoplankton, our results suggest different structuring of the microbial food chain in N-limited relative to P-limited environments.

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