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Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies

Lookup NU author(s): Professor Sam Wilson

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2019, The Author(s).Trichodesmium is an important dinitrogen (N2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N2 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 N2 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 ~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.

Publication metadata

Author(s): Klawonn I, Eichner MJ, Wilson ST, Moradi N, Thamdrup B, Kummel S, Gehre M, Khalili A, Grossart H-P, Karl DM, Ploug H

Publication type: Article

Publication status: Published

Journal: ISME Journal

Year: 2020

Volume: 14

Issue: 2

Pages: 399-412

Print publication date: 01/02/2020

Online publication date: 21/10/2019

Acceptance date: 11/09/2019

Date deposited: 16/12/2021

ISSN (print): 1751-7362

ISSN (electronic): 1751-7370

Publisher: Springer Nature

URL: https://doi.org/10.1038/s41396-019-0514-9

DOI: 10.1038/s41396-019-0514-9

PubMed id: 31636364

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