JPR Advance Access originally published online on January 23, 2007
Journal of Plankton Research 2007 29(3):263-274; doi:10.1093/plankt/fbm013
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Physiological responses of Sargasso Sea picoplankton to nanomolar nitrate perturbations


1 Department of Natural and Social Sciences, University of Maine at Augusta, Maine 04330, USA 2 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: trees{at}nurc.nato.int
Received on August 30, 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 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.
This manuscript is dedicated to C. Garside (Deceased), colleague and friend.
Present Address: Nato Undersea Research Centre, 19138 La Spezia, Italy