Diazotrophs are overlooked contributors to carbon and nitrogen export to the deep ocean

Type Article
Date 2023-01
Language English
Author(s) Bonnet SophieORCID1, Benavides Mar1, 2, Le Moigne Frédéric A. C.ORCID1, 3, Camps Mercedes1, Torremocha Antoine1, Grosso Olivier1, Dimier Céline4, Spungin Dina5, Berman-Frank Ilana5, Garczarek LaurenceORCID6, Cornejo-Castillo Francisco M.ORCID6, 7
Affiliation(s) 1 : Aix Marseille University, Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, France
2 : Turing Center for Living Systems, Aix-Marseille University, 13009, Marseille, France
3 : LEMAR, Laboratoire des sciences de l’environnement marin, UMR6539, CNRS, UBO, IFREMER, IRD, 29280, Plouzané, Technopôle Brest-Iroise, France
4 : Laboratoire d’Océanographie de Villefranche (LOV), Sorbonne Université, CNRS, 06230, Villefranche sur mer, France
5 : University of Haifa, The Leon H. Charney School of Marine Sciences, Haifa, 3498838, Israel
6 : Sorbonne Université, CNRS, UMR 7144 Adaptation and Diversity in the Marine Environment (AD2M), Station Biologique de Roscoff (SBR), Roscoff, France
7 : Institut de Ciènces del Mar (ICM-CSIC), E08003, Barcelona, Spain
Source Isme Journal (1751-7362) (Springer Science and Business Media LLC), 2023-01 , Vol. 17 , N. 1 , P. 47-58
DOI 10.1038/s41396-022-01319-3
WOS© Times Cited 13
Abstract

Diazotrophs are widespread microorganisms that alleviate nitrogen limitation in 60% of our oceans, thereby regulating marine productivity. Yet, the group-specific contribution of diazotrophs to organic matter export has not been quantified, which so far has impeded an accurate assessment of their impact on the biological carbon pump. Here, we examine the fate of five groups of globally-distributed diazotrophs by using an original combination of mesopelagic particle sampling devices across the subtropical South Pacific Ocean. We demonstrate that cyanobacterial and non-cyanobacterial diazotrophs are exported down to 1000 m depth. Surprisingly, group-specific export turnover rates point to a more efficient export of small unicellular cyanobacterial diazotrophs (UCYN) relative to the larger and filamentous Trichodesmium. Phycoerythrin-containing UCYN-B and UCYN-C-like cells were recurrently found embedded in large (>50 µm) organic aggregates or organized into clusters of tens to hundreds of cells linked by an extracellular matrix, presumably facilitating their export. Beyond the South Pacific, our data are supported by analysis of the Tara Oceans metagenomes collected in other ocean basins, extending the scope of our results globally. We show that, when diazotrophs are found in the euphotic zone, they are also systematically present in mesopelagic waters, suggesting their transport to the deep ocean. We thus conclude that diazotrophs are a significant part of the carbon sequestered in the deep ocean and, therefore, they need to be accounted in regional and global estimates of export.

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How to cite 

Bonnet Sophie, Benavides Mar, Le Moigne Frédéric A. C., Camps Mercedes, Torremocha Antoine, Grosso Olivier, Dimier Céline, Spungin Dina, Berman-Frank Ilana, Garczarek Laurence, Cornejo-Castillo Francisco M. (2023). Diazotrophs are overlooked contributors to carbon and nitrogen export to the deep ocean. Isme Journal, 17(1), 47-58. Publisher's official version : https://doi.org/10.1038/s41396-022-01319-3 , Open Access version : https://archimer.ifremer.fr/doc/00795/90702/