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Phytoplankton responses to bacterially regenerated iron in a Southern Ocean eddy

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Fourquez, M, Strzepek, RF ORCID: 0000-0002-6442-7121, Ellwood, MJ, Hassler, C, Cabanes, D, Eggins, S, Pearce, I, Deppeler, S ORCID: 0000-0003-2213-2656, Trull, TW, Boyd, PW ORCID: 0000-0001-7850-1911 and Bressac, M ORCID: 0000-0003-3075-3137 2022 , 'Phytoplankton responses to bacterially regenerated iron in a Southern Ocean eddy' , Microorganisms, vol. 10, no. 8 , pp. 1-20 , doi: 10.3390/microorganisms10081655.

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Abstract

In the Subantarctic sector of the Southern Ocean, vertical entrainment of iron (Fe) triggers the seasonal productivity cycle but diminishing physical supply during the spring to summer transition forces microbial assemblages to rapidly acclimate. Here, we tested how phytoplankton and bacteria within an isolated eddy respond to different dissolved Fe (DFe)/ligand inputs. We used three treatments: one that mimicked the entrainment of new DFe (Fe-NEW), another in which DFe was supplied from bacterial regeneration of particles (Fe-REG), and a control with no addition of DFe (Fe-NO). After 6 days, 3.5 (Fe-NO, Fe-NEW) to 5-fold (Fe-REG) increases in Chlorophyll a were observed. These responses of the phytoplankton community were best explained by the differences between the treatments in the amount of DFe recycled during the incubation (Fe-REG, 15% recycled c.f. 40% Fe-NEW, 60% Fe-NO). This additional recycling was more likely mediated by bacteria. By day 6, bacterial production was comparable between Fe-NO and Fe-NEW but was approximately two-fold higher in Fe-REG. A preferential response of phytoplankton (haptophyte-dominated) relative to high nucleic acid (HNA) bacteria was also found in the Fe-REG treatment while the relative proportion of diatoms increased faster in the Fe-NEW and Fe-NO treatments. Comparisons between light and dark incubations further confirmed the competition between picophytoplankton and HNA for DFe. Overall, our results demonstrate great versatility by microorganisms to use different Fe sources that results in highly efficient Fe recycling within surface waters. This study also encourages future research to further investigate the interactions between functional groups of microbes (e.g. HNA and cyanobacteria) to better constraint modeling in Fe and carbon biogeochemical cycles.

Item Type: Article
Authors/Creators:Fourquez, M and Strzepek, RF and Ellwood, MJ and Hassler, C and Cabanes, D and Eggins, S and Pearce, I and Deppeler, S and Trull, TW and Boyd, PW and Bressac, M
Keywords: iron regeneration, particles, Southern Ocean, eddies, vertical supply, Subantarctic
Journal or Publication Title: Microorganisms
Publisher: MDPIAG
ISSN: 2076-2607
DOI / ID Number: 10.3390/microorganisms10081655
Copyright Information:

Copyright 2022 by the authors. Licensee MDPI, Basel, Switzerland.This article is an open access article distributed under the terms andconditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)

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