In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)

In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)

<p>Here we report N<sub>2</sub> fixation rates from a  ∼ &thinsp;4000&thinsp;km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east tran...

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Main Authors: S. Bonnet, M. Caffin, H. Berthelot, O. Grosso, M. Benavides, S. Helias-Nunige, C. Guieu, M. Stenegren, R. A. Foster
Format: Article
Language:English
Published: Copernicus Publications 2018-07-01
Series:Biogeosciences
Online Access:https://www.biogeosciences.net/15/4215/2018/bg-15-4215-2018.pdf
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spelling doaj-87c76ec8abac4694bbde8024092dac602020-11-24T23:11:22ZengCopernicus PublicationsBiogeosciences1726-41701726-41892018-07-01154215423210.5194/bg-15-4215-2018In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)S. Bonnet0S. Bonnet1M. Caffin2H. Berthelot3H. Berthelot4O. Grosso5M. Benavides6S. Helias-Nunige7C. Guieu8C. Guieu9M. Stenegren10R. A. Foster11Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Noumea, New CaledoniaAix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, FranceAix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, FranceAix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, FranceLaboratoire des sciences de l'énvironnement marin, IUEM, Université de Brest-UMR 6539 CNRS/UBO/IRD/Ifremer, Plouzané, FranceAix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, FranceMarine Biology Section, Department of Biology, University of Copenhagen, 3000 Helsingør, DenmarkAix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UM 110, 13288, Marseille, FranceSorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV), 06230 Villefranche-sur-Mer, FranceCenter for Prototype Climate Modeling, New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab EmiratesDepartment of Ecology, Environment, and Plant Sciences, Stockholm University, Stockholm, 10690, Sweden Department of Ecology, Environment, and Plant Sciences, Stockholm University, Stockholm, 10690, Sweden <p>Here we report N<sub>2</sub> fixation rates from a  ∼ &thinsp;4000&thinsp;km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east transect from 160°&thinsp;E to 160°&thinsp;W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultra-oligotrophy in the South Pacific Gyre (GY) waters. N<sub>2</sub> fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631&thinsp;±&thinsp;286&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup> (range 196–1153&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup>) in MA waters and of 85&thinsp;±&thinsp;79&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup> (range 18–172&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup>) in GY waters. Two cyanobacteria, the larger colonial filamentous <i>Trichodesmium</i> and the smaller UCYN-B, dominated the enumerated diazotroph community ( &gt; &thinsp;80&thinsp;%) and gene expression of the <i>nifH</i> gene (cDNA&thinsp; &gt; &thinsp;10<sup>5</sup> <i>nifH</i> copies L<sup>−1</sup>) in MA waters. Single-cell isotopic analyses performed by nanoscale secondary ion mass spectrometry (nanoSIMS) at selected stations revealed that <i>Trichodesmium</i> was always the major contributor to N<sub>2</sub> fixation in MA waters, accounting for 47.1–83.8&thinsp;% of bulk N<sub>2</sub> fixation. The most plausible environmental factors explaining such exceptionally high rates of N<sub>2</sub> fixation in MA waters are discussed in detail, emphasizing the role of macro- and micro-nutrient (e.g., iron) availability, seawater temperature and currents.</p>https://www.biogeosciences.net/15/4215/2018/bg-15-4215-2018.pdf
collection DOAJ
language English
format Article
sources DOAJ
author S. Bonnet
S. Bonnet
M. Caffin
H. Berthelot
H. Berthelot
O. Grosso
M. Benavides
S. Helias-Nunige
C. Guieu
C. Guieu
M. Stenegren
R. A. Foster
spellingShingle S. Bonnet
S. Bonnet
M. Caffin
H. Berthelot
H. Berthelot
O. Grosso
M. Benavides
S. Helias-Nunige
C. Guieu
C. Guieu
M. Stenegren
R. A. Foster
In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
Biogeosciences
author_facet S. Bonnet
S. Bonnet
M. Caffin
H. Berthelot
H. Berthelot
O. Grosso
M. Benavides
S. Helias-Nunige
C. Guieu
C. Guieu
M. Stenegren
R. A. Foster
author_sort S. Bonnet
title In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
title_short In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
title_full In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
title_fullStr In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
title_full_unstemmed In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N<sub>2</sub> fixation (OUTPACE cruise)
title_sort in-depth characterization of diazotroph activity across the western tropical south pacific hotspot of n<sub>2</sub> fixation (outpace cruise)
publisher Copernicus Publications
series Biogeosciences
issn 1726-4170
1726-4189
publishDate 2018-07-01
description <p>Here we report N<sub>2</sub> fixation rates from a  ∼ &thinsp;4000&thinsp;km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east transect from 160°&thinsp;E to 160°&thinsp;W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultra-oligotrophy in the South Pacific Gyre (GY) waters. N<sub>2</sub> fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631&thinsp;±&thinsp;286&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup> (range 196–1153&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup>) in MA waters and of 85&thinsp;±&thinsp;79&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup> (range 18–172&thinsp;µmol N m<sup>−2</sup> d<sup>−1</sup>) in GY waters. Two cyanobacteria, the larger colonial filamentous <i>Trichodesmium</i> and the smaller UCYN-B, dominated the enumerated diazotroph community ( &gt; &thinsp;80&thinsp;%) and gene expression of the <i>nifH</i> gene (cDNA&thinsp; &gt; &thinsp;10<sup>5</sup> <i>nifH</i> copies L<sup>−1</sup>) in MA waters. Single-cell isotopic analyses performed by nanoscale secondary ion mass spectrometry (nanoSIMS) at selected stations revealed that <i>Trichodesmium</i> was always the major contributor to N<sub>2</sub> fixation in MA waters, accounting for 47.1–83.8&thinsp;% of bulk N<sub>2</sub> fixation. The most plausible environmental factors explaining such exceptionally high rates of N<sub>2</sub> fixation in MA waters are discussed in detail, emphasizing the role of macro- and micro-nutrient (e.g., iron) availability, seawater temperature and currents.</p>
url https://www.biogeosciences.net/15/4215/2018/bg-15-4215-2018.pdf
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