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Cycling of organic nitrogen in marine plankton communities studied in enclosed water columns
Authors:J. T. Hollibaugh  A. B. Carruthers  J. A. Fuhrman  F. Azam
Affiliation:(1) Scripps Institution of Oceanography, Institute of Marine Resources, A-018, University of California, San Diego, La Jolla, California;(2) Department of Oceanography, University of British Columbia, V6T 1W5 Vancouver, British Columbia, Canada
Abstract:Concentrations of fluorescamine-positive substances (primary amines) and turnover rates of L-leucine pools were measured concurrently in seawater samples taken from 1300 m3 plastic enclosures moored in Saanich Inlet, British Columbia, Canada. Concentration and turnover rates of dissolved free amino acids were calculated and then used to determine the instantaneous flux of dissolved free amino acids, which ranged from 0.09 to 2.42 mgrM d-1 (i.e.,5 to 145 mgrgC l-1 d-1). This flux was highest in the euphotic zone, and was related to net primary production but not to the type of dominant primary producer. Comparison of the flux to changes in the concentration of ammonia in deep water suggested that amino acid degradation accounted for 60% of the flux into the ammonia pool. For a given sample, the amino acid carbon flux ranged from 17 to 210% (mean=78%) of the primary production. Such fluxes of amino acid carbon, if used exclusively by the bacterioplankton, would give growth rates ranging from 0.3 to 3.0 (mean=1.7) bacterial doublings d-1. These calculations indicate that a large fraction of the community carbon and nitrogen flux passes through the bacterioplankton.
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