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Aquatic Microbial Ecology

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AME 72:195-213 (2014)  -  DOI:

Picoeukaryote distribution in relation to nitrate uptake in the oceanic nitracline

Stuart C. Painter1,*, Matthew D. Patey2, Glen A. Tarran3, Sinhué Torres-Valdés1

1National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
2Chemistry Department, University of Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain
3Plymouth Marine Laboratory, The Hoe, Prospect Place, Plymouth PL1 3DH, UK
*Corresponding author:

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 (Vmax) 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.

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