Factors Controlling the Year-Round Variability in Carbon Flux Through Bacteria in a Coastal Marine System |
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Authors: | Laura Alonso-Sáez Evaristo Vázquez-Domínguez Clara Cardelús Jarone Pinhassi M Montserrat Sala Itziar Lekunberri Vanessa Balagué Maria Vila-Costa Fernando Unrein Ramon Massana Rafel Simó Josep M Gasol |
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Institution: | (1) Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar-CMIMA, CSIC, Barcelona, Catalunya, Spain;(2) Department of Ecology and Evolution, Uppsala University, Uppsala, Sweden;(3) Present address: Marine Microbiology, Department of Biology and Environmental Sciences, University of Kalmar, Kalmar, Sweden;(4) Present address: Department of Marine Sciences, University of Georgia, Athens, Georgia, USA;(5) Present address: IIB-INTECH, Chascomús, Buenos Aires, Argentina |
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Abstract: | Data from several years of monthly samplings are combined with a 1-year detailed study of carbon flux through bacteria at
a NW Mediterranean coastal site to delineate the bacterial role in carbon use and to assess whether environmental factors
or bacterial assemblage composition affected the in situ rates of bacterial carbon processing. Leucine (Leu) uptake rates
as an estimate of bacterial heterotrophic production (BHP)] showed high interannual variability but, on average, lower values
were found in winter (around 50 pM Leu−1 h−1) as compared to summer (around 150 pM Leu−1 h−1). Leu-to-carbon conversion factors ranged from 0.9 to 3.6 kgC mol Leu−1, with generally higher values in winter. Leu uptake was only weakly correlated to temperature, and over a full-year cycle
(in 2003), Leu uptake peaked concomitantly with winter chlorophyll a (Chl a) maxima, and in periods of high ectoenzyme activities in spring and summer. This suggests that both low molecular weight
dissolved organic matter (DOM) released by phytoplankton, and high molecular weight DOM in periods of low Chl a, can enhance BHP. Bacterial respiration (BR, range 7–48 μg C l−1 d−1) was not correlated to BHP or temperature, but was significantly correlated to DOC concentration. Total bacterial carbon
demand (BHP plus BR) was only met by dissolved organic carbon produced by phytoplankton during the winter period. We measured
bacterial growth efficiencies by the short-term and the long-term methods and they ranged from 3 to 42%, increasing during
the phytoplankton blooms in winter (during the Chl a peaks), and in spring. Changes in bacterioplankton assemblage structure (as depicted by denaturing gradient gel electrophoresis
fingerprinting) were not coupled to changes in ecosystem functioning, at least in bacterial carbon use. |
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Keywords: | bacterioplankton production respiration carbon marine seasonality growth efficiency coastal |
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