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Microbial competition in the subpolar southern ocean: an Fe–C Co-limitation experiment

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Fourquez, M, Bressac, M ORCID: 0000-0003-3075-3137, Deppeler, SL ORCID: 0000-0003-2213-2656, Ellwood, M, Obernosterer, I, Trull, TW and Boyd, PW ORCID: 0000-0001-7850-1911 2020 , 'Microbial competition in the subpolar southern ocean: an Fe–C Co-limitation experiment' , Frontiers in Marine Science, vol. 6, no. JAN , pp. 1-15 , doi: 10.3389/fmars.2019.00776.

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Abstract

Iron (Fe) is a paradox in the modern ocean – it is central to many life-critical enzymes but is scarce across most surface waters. The high cellular demand and low bioavailability of Fe likely puts selective pressure on marine microorganisms. Previous observations suggest that heterotrophic bacteria are outcompeted by small diatoms for Fe supply in the subantarctic zone of Southern Ocean, thereby challenging the idea of heterotrophic bacteria being more competitive than phytoplankton in the access to this trace metal. To test this hypothesis, incubation experiments were carried out at the Southern Ocean Time Series site (March–April 2016). We investigated (a) whether dissolved organic carbon (DOC), dissolved Fe, or both limit the growth of heterotrophic bacteria and, (b) if the presence of potential competitors has consequences on the bacterial Fe acquisition. We observed a pronounced increase in both bulk and cell-specific bacterial production in response to single (+C) and combined (+Fe+C) additions, but no changes in these rates when only Fe was added (+Fe). Moreover, we found that +Fe+C additions promoted increases in cell-specific bacterial Fe uptake rates, and these increases were particularly pronounced (by 13-fold) when phytoplankton were excluded from the incubations. These results suggest that auto- and heterotrophs could compete for Fe when DOC limitation of bacterial growth is alleviated. Such interactions between primary producers and nutrient-recyclers are unexpected drivers for the duration and magnitude of phytoplankton blooms in the Southern Ocean.

Item Type: Article
Authors/Creators:Fourquez, M and Bressac, M and Deppeler, SL and Ellwood, M and Obernosterer, I and Trull, TW and Boyd, PW
Keywords: iron, carbon, Southern Ocean, competition, heterotrophic bacteria, pico-nanoplankton, Fe uptake, bacterial production
Journal or Publication Title: Frontiers in Marine Science
Publisher: Frontiers Research Foundation
ISSN: 2296-7745
DOI / ID Number: 10.3389/fmars.2019.00776
Copyright Information:

Copyright © 2020 Fourquez, Bressac, Deppeler, Ellwood, Obernosterer, Trull andBoyd. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

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