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Competition for inorganic and organic forms of nitrogen and phosphorous between phytoplankton and bacteria during an Emiliania huxleyi spring bloom
1Department of Biology, University of Bergen, Jahnebakken 5, PO Box 7800, 5020 Bergen, Norway
2Leibniz Institute of Freshwater Ecology and Inland Fisheries, Department of Limnology of Stratified Lakes, Alte Fischehuette 2, 16775 Stechlin, Germany
3Laboratoire d'Océanographie Chimique et Géochimie des Eaux, Université Libre de Bruxelles, Campus Plaine – CP 208, 1050 Brussels, Belgium
4Laboratoire 'Mer, Molécule, Santé', EA 2160, EA2663, Université de Nantes, BP 92208, 44322 Nantes, France
*present address: Department of Mathematics and Natural Sciences, Faculty of Science and Technology, University of Stavanger, 4036 Stavanger, Norway
**present address: Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway
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.
Final Revised Paper (PDF, 406 KB) Discussion Paper (BGD)
Citation: Løvdal, T., Eichner, C., Grossart, H.-P., Carbonnel, V., Chou, L., Martin-Jézéquel, V., and Thingstad, T. F.: Competition for inorganic and organic forms of nitrogen and phosphorous between phytoplankton and bacteria during an Emiliania huxleyi spring bloom, Biogeosciences, 5, 371-383, 2008. Bibtex EndNote Reference Manager
