Seasonal patterns of urea regeneration by size-fractionated microheterotrophs in well-mixed temperate coastal waters |
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Authors: | L'Helguen S; Slawyk G; Le Corre P |
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Institution: | 1 Laboratoire de Chimie Marine, Observatoire Océanologique de Roscoff, CNRS/INSU UMR 7127 Et Université de Bretagne Occidentale, BP 74, 29682 Roscoff, Cedex, France and 2 Laboratoire DOcéAnographie Et de Biogéochimie, UMR CNRS 6535, Campus de Luminy, Case 901, 13288 Marseille, Cedex 09, France |
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Abstract: | Urea regeneration by size-fractionated plankton was measuredover an annual cycle at a coastal station in the permanentlywell-mixed waters of the western English Channel. Rates of urearegeneration in the <200 µm fraction varied from 0.6to 20.6 nmol N L1 h1. Regeneration rates werelowest in winter and highest in summer. The ratio of the ratesof regeneration to uptake of urea was close to 1 on all time(seasonal and nycthemeral), and space (vertical) scales indicatingthat regeneration by microheterotrophs supplied the totalityof urea used by phytoplankton. On an annual basis, urea regeneratedby the microheterotrophs (0.98 mol N m2 year1)was equivalent to 33% of the total regenerated N (urea + ammonium).The major part of urea regeneration was due to the nanoplankton(51%) and microplankton fractions (36%). Regeneration of ureain the picoplankton was detectable only from April to Octoberand represented, on an average, 25% of the total urea regeneratedduring this period. Urea regeneration in micro- and nanoplanktonfractions was mainly associated with ciliates and in the picoplanctonfraction with bacteria. |
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