NanoSIMS single cell analyses reveal the contrasting nitrogen sources for small phytoplankton

Type Article
Date 2019-03
Language English
Author(s) Berthelot Hugo1, Duhamel Solange2, L’helguen Stéphane1, Maguer Jean-Francois1, Wang Seaver3, Cetinić Ivona5, Cassar Nicolas1, 3
Affiliation(s) 1 : Laboratoire des Sciences de l’Environnement Marin (LEMAR), UMR 6539 UBO/CNRS/IRD/IFREMER, Institut Universitaire Européen de la Mer (IUEM), Brest, France
2 : Division of Biology and Paleo Environment, Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA
3 : Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA
4 : NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Code 616, Greenbelt, MD, USA
5 : GESTAR/Universities Space Research Association, Columbia, MD, USA
Source Isme Journal (1751-7362) (Springer Nature America, Inc), 2019-03 , Vol. 13 , N. 3 , P. 651-662
DOI 10.1038/s41396-018-0285-8

Nitrogen (N) is a limiting nutrient in vast regions of the world’s oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO3−), ammonium (NH4+) and urea uptake rates at the single cell level in photosynthetic pico-eukaryotes (PPE) and the cyanobacteria Prochlorococcus and Synechococcus. To that end, we used dual 15N and 13C-labeled incubation assays coupled to flow cytometry cell sorting and nanoSIMS analysis on samples collected in the North Pacific Subtropical Gyre (NPSG) and in the California Current System (CCS). Based on these analyses, we found that photosynthetic growth rates (based on C fixation) of PPE were higher in the CCS than in the NSPG, while the opposite was observed for Prochlorococcus. Reduced forms of N (NH4+ and urea) accounted for the majority of N acquisition for all the groups studied. NO3− represented a reduced fraction of total N uptake in all groups but was higher in PPE (17.4 ± 11.2% on average) than in Prochlorococcus and Synechococcus (4.5 ± 6.5 and 2.9 ± 2.1% on average, respectively). This may in part explain the contrasting biogeography of these picoplankton groups. Moreover, single cell analyses reveal that cell-to-cell heterogeneity within picoplankton groups was significantly greater for NO3− uptake than for C fixation and NH4+ uptake. We hypothesize that cellular heterogeneity in NO3− uptake within groups facilitates adaptation to the fluctuating availability of NO3− in the environment.

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