Longitudinal variability of diazotroph abundances in the subtropical North Atlantic Ocean

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