In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N2 fixation (OUTPACE cruise)

Type Article
Date 2018-07
Language English
Author(s) Bonnet Sophie1, 2, Caffin Mathieu2, Berthelot Hugo2, 3, Grosso Olivier2, Benavides Mar4, Helias-Nunige Sandra2, Guieu Cecile5, 6, Stenegren Marcus7, Foster Rachel Ann7
Affiliation(s) 1 : Aix Marseille Univ, Univ Toulon, CNRS, IRD,MIO UM 110, Noumea 13288, New Caledonia.
2 : Aix Marseille Univ, Univ Toulon, CNRS, IRD,MIO UM 110, F-13288 Marseille, France.
3 : Univ Brest, UMR 6539, Lab Sci Environm Marin, CNRS,UBO,IRD,Ifremer,IUEM, Plouzane, France.
4 : Univ Copenhagen, Dept Biol, Marine Biol Sect, DK-3000 Helsingor, Denmark.
5 : Sorbonne Univ, UPMC Univ Paris 06, CNRS, LOV, F-06230 Villefranche Sur Mer, France.
6 : New York Univ Abu Dhabi, Ctr Prototype Climate Modeling, POB 129188, Abu Dhabi, U Arab Emirates.
7 : Stockholm Univ, Dept Ecol Environm & Plant Sci, S-10690 Stockholm, Sweden.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-07 , Vol. 15 , N. 13 , P. 4215-4232
DOI 10.5194/bg-15-4215-2018
WOS© Times Cited 22
Note Special issue Interactions between planktonic organisms and biogeochemical cycles across trophic and N2 fixation gradients in the western tropical South Pacific Ocean: a multidisciplinary approach (OUTPACE experiment) Editor(s): T. Moutin, S. Bonnet, K. Richards, D. G. Capone, E. Marañón, and L. Mémery
Abstract

Here we report N2 fixation rates from a  ∼ 4000km 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°E to 160°W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultra-oligotrophy in the South Pacific Gyre (GY) waters. N2 fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631±286µmol N m−2 d−1 (range 196–1153µmol N m−2 d−1) in MA waters and of 85±79µmol N m−2 d−1 (range 18–172µmol N m−2 d−1) in GY waters. Two cyanobacteria, the larger colonial filamentous Trichodesmium and the smaller UCYN-B, dominated the enumerated diazotroph community ( > 80%) and gene expression of the nifH gene (cDNA > 105 nifH copies L−1) in MA waters. Single-cell isotopic analyses performed by nanoscale secondary ion mass spectrometry (nanoSIMS) at selected stations revealed that Trichodesmium was always the major contributor to N2 fixation in MA waters, accounting for 47.1–83.8% of bulk N2 fixation. The most plausible environmental factors explaining such exceptionally high rates of N2 fixation in MA waters are discussed in detail, emphasizing the role of macro- and micro-nutrient (e.g., iron) availability, seawater temperature and currents.

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Discussion paper DOI 10.5194/bg-2017-567 29 1 MB Open access
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Bonnet Sophie, Caffin Mathieu, Berthelot Hugo, Grosso Olivier, Benavides Mar, Helias-Nunige Sandra, Guieu Cecile, Stenegren Marcus, Foster Rachel Ann (2018). In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N2 fixation (OUTPACE cruise). Biogeosciences, 15(13), 4215-4232. Publisher's official version : https://doi.org/10.5194/bg-15-4215-2018 , Open Access version : https://archimer.ifremer.fr/doc/00419/53049/