Longitudinal variability of diazotroph abundances in the subtropical North Atlantic Ocean

• Published in: Journal of Plankton Research
• Main Authors: Benavides, Mar, Moisander, Pia H., Daley, Meaghan C., Bode, Antonio, Aristegui, Javier
• Other Authors: Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.ES]Environmental Sciences/Environment and Society; [SDE.MCG]Environmental Sciences/Global Changes; [SDE.IE]Environmental Sciences/Environmental Engineering; North Atlantic
• Online Access: https://hal.science/hal-01443608; https://doi.org/10.1093/plankt/fbv121

International audience Diazotrophy-related studies in the North Atlantic have largely focused on its western tropical area, leaving the subtropics and the east undersampled. We studied the longitudinal distribution of Trichodesmium, UCYN-A, UCYN-B, the putative Gammaproteobacterium g-24774A11 and Richelia (Het1) along 24.5 degrees N, using quantitative polymerase chain reaction on different size fractions (10, 10-3 and 3-0.2 mm) and additional filament counts for Trichodesmium. Trichodesmium was the most abundant phylotype, followed by UCYN-A, gamma-24774A11 and Het1, with maximum abundances of 8.8 x 10(5), 2.0 x 10(5), 3.3 x 10(3) and 3.4 x 10(2) nifH copies L-1, respectively, whereas UCYN-B was mostly undetected. A clear shift in the diazotroph community was observed at similar to 30 degrees W, coinciding with the transition between the North Atlantic Subtropical Gyre boundary and inner core. This transition zone divided the transect into an eastern half dominated by UCYN-A and western half dominated by Trichodesmium and gamma-24774A11. gamma-24774A11 was only detected in the 10-3 mu m fraction, suggesting their association with larger microbes or aggregates. Our results indicate that typical size fractionation by 10 mu m is not optimal for reconciling diazotroph phylotypes to N-2 fixation rates and that non-cyanobacterial diazotrophs may contribute importantly to bulk diazotrophic activity in the western subtropical North Atlantic.