AME 72:195-213 (2014)  -  DOI: https://doi.org/10.3354/ame01695

ABSTRACT: We investigated the relationship between picoeukaryote phytoplankton (<2 µm) and the deep layer of new production (NO₃^- uptake) in the nitracline of the eastern subtropical North Atlantic Ocean. Indices of NO₃^- uptake kinetics obtained within the lower 15% of the euphotic zone demonstrate that subsurface NO₃^- uptake maxima are coincident with localised peaks in maximum uptake rates (V_max) and, crucially, with maximum picoeukaryote abundance. The mean rate of NO₃^- utilization at the nitracline is typically 10-fold higher than in surface waters despite much lower in situ irradiance. These observations confirm a high affinity for NO₃^-, most likely by the resident picoeukaryote community, and we conservatively estimate mean cellular uptake rates of between 0.27 and 1.96 fmol NO₃^- cell^-1 h^-1. Greater scrutiny of the taxonomic composition of the picoeukaryote group is required to further understand this deep layer of new production and its importance for nitrogen cycling and export production, given longstanding assumptions that picoplankton do not contribute directly to export fluxes.

KEY WORDS: Nitracline · Picoeukaryote · Nitrate uptake · Subtropical Atlantic Ocean

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Cite this article as: Painter SC, Patey MD, Tarran GA, Torres-Valdés S (2014) Picoeukaryote distribution in relation to nitrate uptake in the oceanic nitracline. Aquat Microb Ecol 72:195-213. https://doi.org/10.3354/ame01695 Export citation Share:    Facebook - - linkedIn