New insights into the distributions of nitrogen fixation and diazotrophs revealed by high-resolution sensing and sampling methods

• Published in: The ISME Journal
• Main Authors: Tang, Weiyi, Cerdan-Garcia, Elena, Berthelot, Hugo, Polyviou, Despo, Wang, Seaver, Baylay, Alison, Whitby, Hannah, Planquette, Helene, Mowlem, Matthew, Robidart, Julie, Cassar, Nicolas
• Other Authors: Department of Earth and Ocean Sciences Durham (EOS), Duke University Durham, National Oceanography Centre Southampton (NOC), University of Southampton, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Duke Graduate School, Duke Interdisciplinary Studies through The Dissertation Research Travel Award: Graduate Student Training Enhancement Grant (GSTEG), "Laboratoire d'Excellence" LabexMER ANR-10-LABX-19, French government under the program "Investissements d'Avenir"French National Research Agency (ANR), NERCNERC Natural Environment Research Council NE/N006496/1, AtlantOS (Horizon 2020), NSF-CAREER grantNational Science Foundation (NSF)NSF - Office of the Director (OD) 1350710, ANR-10-LABX-0019,LabexMER,LabexMER Marine Excellence Research: a changing ocean(2010), European Project: 633211,H2020,H2020-BG-2014-2,AtlantOS(2015)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; North Atlantic
• Online Access: https://hal.science/hal-02933395; https://hal.science/hal-02933395/document; https://hal.science/hal-02933395/file/74648.pdf; https://doi.org/10.1038/s41396-020-0703-6

International audience Nitrogen availability limits marine productivity across large ocean regions. Diazotrophs can supply new nitrogen to the marine environment via nitrogen (N-2) fixation, relieving nitrogen limitation. The distributions of diazotrophs and N-2 fixation have been hypothesized to be generally controlled by temperature, phosphorus, and iron availability in the global ocean. However, even in the North Atlantic where most research on diazotrophs and N-2 fixation has taken place, environmental controls remain contentious. Here we measure diazotroph composition, abundance, and activity at high resolution using newly developed underway sampling and sensing techniques. We capture a diazotrophic community shift from Trichodesmium to UCYN-A between the oligotrophic, warm (25-29 degrees C) Sargasso Sea and relatively nutrient-enriched, cold (13-24 degrees C) subpolar and eastern American coastal waters. Meanwhile, N-2 fixation rates measured in this study are among the highest ever recorded globally and show significant increase with phosphorus availability across the transition from the Gulf Stream into subpolar and coastal waters despite colder temperatures and higher nitrate concentrations. Transcriptional patterns in both Trichodesmium and UCYN-A indicate phosphorus stress in the subtropical gyre. Over this iron-replete transect spanning the western North Atlantic, our results suggest that temperature is the major factor controlling the diazotrophic community structure while phosphorous drives N-2 fixation rates. Overall, the occurrence of record-high UCYN-A abundance and peak N-2 fixation rates in the cold coastal region where nitrate concentrations are highest (similar to 200 nM) challenges current paradigms on what drives the distribution of diazotrophs and N-2 fixation.