Diazotroph derived nitrogen supports diatom growth in the South West Pacific: A quantitative study using nanoSIMS

Sophie Bonnet, Hugo Berthelot, Kendra Turk-Kubo, Véronique Cornet-Barthaux, Sarah Fawcett, Ilana Berman-Frank, Aude Barani, Gérald Grégori, Julien Dekaezemacker, Mar Benavides, Douglas G. Capone

Research output: Contribution to journalArticlepeer-review

Abstract

Nitrogen is essential for life but is often a major limiting nutrient for growth in the ocean. Biological dinitrogen fixation is a major source of new nitrogen to surface waters and promotes marine productivity. Yet the fate of diazotroph-derived nitrogen (DDN) in marine ecosystems has been poorly studied, and its transfer to auto- and heterotrophic plankton has not been measured. Here, we use high-resolution nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labelling and flow cytometry cell sorting to examine the DDN transfer to specific groups of natural phytoplankton and bacteria during three diazotroph blooms dominated by the cyanobacterium Trichodesmium spp. in the South West Pacific. During these experiments, 13% ± 2% to 48% ± 5% of the fixed 15N2 was released into the dissolved pool and 6% ± 1% to 8% ± 2% of this DDN was transferred to non-diazotrophic plankton after 48 h. The primary beneficiaries of this DDN were diatoms (45% ± 4% to 61% ± 38%) and bacteria (22% ± 27% to 38% ± 12%), followed by pico-phytoplankton (3% ± 1% to 21% ± 14%). The DDN was quickly converted to non-diazotrophic plankton biomass, in particular that of diatoms, which increased in abundance by a factor of 1.4–15 over the course of the three experiments. The single-cell approach we used enabled quantification of the actual transfer of DDN to specific groups of autotrophic and heterotrophic plankton in the surface ocean, revealing a previously unseen level of complexity in the pathways that occur between N2 fixation and the eventual export of DDN from the photic zone.

Original languageEnglish
Pages (from-to)1549-1562
Number of pages14
JournalLimnology and Oceanography
Volume61
Issue number5
DOIs
StatePublished - 1 Sep 2016
Externally publishedYes

Bibliographical note

Funding Information:
We acknowledge the captains and crews of the R/Vs Aldric, Alis and Thompson, the divers from IRD and Cécile Dupouy and Fabrice Lazzaro for their help collecting samples from E1 at sea. The LAMA (LAboratoire des Moyens Analytiques) is thanked for providing nutrient analyzes, F. Van Wambeke for proving bacteria production data, M. Rodier for calculating NH4+ concentrations from E1, and D. Sigman for providing analytical support for the

Publisher Copyright:
© 2016 Association for the Sciences of Limnology and Oceanography

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science

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