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Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise)
1Aix-Marseille Université, Laboratoire d'Océanographie et de Biogéochimie, LOB-UMR 6535 CNRS, OSU/Centre d'Océanologie de Marseille, 13288 Marseille, Cedex 09, France
2Aix-Marseille Université, Laboratoire de Microbiologie, Géochimie et Ecologie Marines, LMGEM-UMR 6117 CNRS, OSU/Centre d'Océanologie de Marseille, 13288 Marseille, Cedex 09, France
3Department of Marine Chemistry and Geochemistry, Wood Hole Oceanographic Institution, MS #4, Wood Hole, MA 02543, USA
4CNRS, Laboratoire d'océanographie de Villefranche, 06230 Villefranche-sur-Mer, France; Université Pierre et Marie Curie-Paris 6, Laboratoire d'océanographie de Villefranche, 06230 Villefranche-sur-mer, France
Abstract. Predicting heterotrophic bacteria and phytoplankton specific growth rates (μ ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton μ. One widely used method is to estimate μ from data obtained on biomass or cell abundance and rates of biomass or cell production. According to Kirchman (2002), the most appropriate approach for estimating μ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate μ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate μ using phosphate (P) data. We showed that particulate phosphate (PartP) can be used to estimate biomass and that the P uptake rate to PartP ratio can be employed to assess μ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of μ for both autotrophic and heterotrophic organisms. We report values of P-based μ in three size fractions (0.2–0.6; 0.6–2 and >2 μm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. P-based μ values were higher in the 0.6–2 μm fraction than in the >2 μm fraction, suggesting that picoplankton-sized cells grew faster than the larger cells, whatever the trophic regime encountered. Picoplankton-sized cells grew significantly faster in the deep chlorophyll maximum layer than in the upper part of the photic zone in the oligotrophic gyre area, suggesting that picoplankton might outcompete >2 μm cells in this particular high-nutrient, low-light environment. P-based μ attributed to free-living bacteria (0.2-0.6 μm) and picoplankton (0.6–2 μm) size-fractions were relatively low (0.11±0.07 d−1 and 0.14±0.04 d−1, respectively) in the Southeast Pacific gyre, suggesting that the microbial community turns over very slowly.
Final Revised Paper (PDF, 1969 KB) Discussion Paper (BGD)
Citation: Duhamel, S., Moutin, T., Van Wambeke, F., Van Mooy, B., Rimmelin, P., Raimbault, P., and Claustre, H.: Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise), Biogeosciences, 4, 941-956, 2007. Bibtex EndNote Reference Manager
