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Aquatic Microbial Ecology

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AME 30:263-274 (2003)  -  doi:10.3354/ame030263

Plankton community composition in relation to availability and uptake of oxidized and reduced nitrogen

Gry Mine Berg1,*, Maija Balode2, Ingrida Purina2, Santa Bekere2, Christian Béchemin3, Serge Y. Maestrini3

1Department of Marine Biogeochemistry, Institut für Meereskunde an der Universität Kiel, Düsternbrookerweg 20, 24105 Kiel, Germany
2Institute of Aquatic Ecology, University of Latvia, 3 Miera Street, Salaspils 2169, Latvia
3Centre de Recherche en Ecologie Marine et Aquaculture de L¹Houmeau (CNRS-IFREMER), BP 5, 17137 L¹Houmeau, France

ABSTRACT: Trends in nitrogen utilization, determined with 15N-labeled substrates, were related to blooms of distinct phytoplankton groups in the Gulf of Riga, Baltic Sea, during May, June and July 1999. The dominant phytoplankton groups included diatoms, cryptophytes, dinoflagellates, and filamentous cyanobacteria. As the water column became progressively more stratified over the growing season, diatoms comprised a smaller proportion of the total phytoplankton assemblage and almost disappeared by late summer. Their disappearance correlated with undetectable surface-water nitrate concentrations and low nitrate uptake rates (5 to 8% of total nitrogen uptake). Diatoms were the only phytoplankton group significantly associated with the uptake of oxidized nitrogen (nitrate). Cryptophytes, filamentous cyanobacteria and dinoflagellates were significantly associated with uptake of reduced nitrogen including ammonium, urea, dissolved free amino acids and adenine. Our results indicate that uptake of oxidized and reduced forms of nitrogen can be separated in time and space due to association with distinct phytoplankton groups.

KEY WORDS: Nitrogen uptake · DON · Nitrate · Diatoms · Cyanobacteria · Cryptophytes · Baltic Sea · Gulf of Riga

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