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Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. IGB-Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany.
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Number of Authors: 112020 (English)In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 14, no 2, p. 399-412Article in journal (Refereed) Published
Abstract [en]

Trichodesmium is an important dinitrogen (N-2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N-2 fixation. However, rates of these transformations and concentration gradients of N compounds in Trichodesmium colonies remain largely unresolved. We combined isotope-tracer incubations, micro-profiling and numeric modelling to explore carbon fixation, N cycling processes as well as oxygen, ammonium and nitrate concentration gradients in individual field-sampled Trichodesmium colonies. Colonies were net-autotrophic, with carbon and N-2 fixation occurring mostly during the day. Ten percent of the fixed N was released as ammonium after 12-h incubations. Nitrification was not detectable but nitrate consumption was high when nitrate was added. The consumed nitrate was partly reduced to ammonium, while denitrification was insignificant. Thus, the potential N transformation network was characterised by fixed N gain and recycling processes rather than denitrification. Oxygen concentrations within colonies were similar to 60-200% air-saturation. Moreover, our modelling predicted steep concentration gradients, with up to 6-fold higher ammonium concentrations, and nitrate depletion in the colony centre compared to the ambient seawater. These gradients created a chemically heterogeneous microenvironment, presumably facilitating diverse microbial metabolisms in millimetre-sized Trichodesmium colonies.

Place, publisher, year, edition, pages
2020. Vol. 14, no 2, p. 399-412
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Biological Sciences
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URN: urn:nbn:se:su:diva-179576DOI: 10.1038/s41396-019-0514-9ISI: 000509197100007PubMedID: 31636364OAI: oai:DiVA.org:su-179576DiVA, id: diva2:1416772
Available from: 2020-03-25 Created: 2020-03-25 Last updated: 2020-03-25Bibliographically approved

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Klawonn, IsabellEichner, Meri J.Wilson, Samuel T.Thamdrup, Bo
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