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JPR Advance Access published online on January 23, 2007
Journal of Plankton Research, doi:10.1093/plankt/fbm013
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© The Author 2007. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Physiological responses of Sargasso Sea picoplankton to nanomolar nitrate perturbations

Hilary E. Glover1, Christopher Garside2,* and Charles C. Trees3,**,

1 Department of Natural and Social Sciences, University of Maine at Augusta, Maine 04330, USA 2 (Deceased) Bigelow Laboratory for Ocean Sciences, W. Boothbay Harbor, Maine 04575, USA 3 Center for Hydro-Optics and Remote Sensing, San Diego State University, San Diego, CA, 92120, USA

Corresponding author: Charles C. Trees, NATO Undersea Research Centre, 19138, La Spezia, Italy Email: trees{at}nurc.nato.int

Received on August 30, 2006; revised on November 28, 2006; accepted on January 12, 2007


  Abstract

A study was conducted in July 1989 at three stations in the northern Sargasso Sea, where picoplankton (< 1 µm) provided approximately half of the standing crop of chlorophyll. Temporal changes in the position of the nitracline at a single location indicated that the vertical supply of nitrate was not at ‘steady-state’ and phytoplankton distributions tracked the nitracline. Our main experimental objective was to examine the short-term effects of ecologically significant nitrate perturbations (+20 ;nM and +100 nM) on the physiology of <1 µm communities growing at low (nanomolar) ambient nitrate concentrations. A chemiluminescent nitrate method was used to measure the time course (up to 4 h) of nitrate disappearance at in situ irradiance, in parallel with measurements of photosynthetic 14CO2 assimilation. Picoplankton growing at <60 ;nM nitrate rapidly responded to nanomolar nitrate supplements with luxury consumption and enhanced photosynthesis in proportion to their ambient nitrate environment. Light-saturated Synechococcus populations from the most nitrate-depleted waters (13 nM) had doubled their cellular rate of photosynthesis after 4 h, in response to a 20 nM nitrate pulse.

Key Words: Sargasso Sea • picophytoplankton • Synechococcus • nitrate • chemiluminescence • photosynthesis • chlorophyll

* This manuscript is dedicated to C. Garside, colleague and friend.

** Current Address, NATO Undersea Research Centre, 19138 La Spezia, Italy

Communicating editor: KJ Flynn


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