PARENT SESSION
Contributed Oral Session 25: Aquatic Trophic Systems II
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 518 A, Level 5, Palais des congrès de Montréal
Incorporating bacterioplankton in the Plankton Ecology Group model of succession of planktonic groups in fresh waters: How bacterioplankton diversity and metabolism vary in relation to abiotic resources and predators?
Cauchie, Henry*,1, Delgoulet, Sébastien1, Jacquet, Véronique1, Bonjean, Nicolas1, Thys, Isabelle1, Hoffmann, Lucien, 1 Centre de Recherche Public-Gabriel Lippmann, Belvaux, Luxembourg
ABSTRACT- The study objective was to determine how bacterioplankton diversity and metabolism connect with the other compartments of the ecosystem along a eutrophication gradient in temperate freshwater reservoirs. Therefore the bacterioplankton diversity and metabolism were monitored in three reservoirs with contrasting trophic status (oligotrophy, mesotrophy and eutrophy). Sampling was conducted during 2003 at high temporal frequency (from once a month to once a week). Bacterioplankton diversity was determined using 16S-DNA DGGE fingerprinting. The following metabolism indicators were monitored: density, biovolume, biomass production, monosaccharide assimilation, glucosidase and chitinase activity. Besides, variables such as temperature, pH, conductivity, nutrient concentration, zooplankton biomass... were monitored. Multivariate analyses were performed in order to determine whether seasonality existed within the reservoirs and whether common patterns were shared between the reservoirs. It appeared that 5 to 6 periods were detected in each reservoir. The intrinsic characteristics of these periods in terms of bacterioplankton metabolism appeared to be similar across reservoirs. Periods of the year were mainly discriminated by biovolume and biomass production. The major biotic and abiotic variables that presumably influence the metabolism dynamics were temperature, nutrients and virus density. On the basis of the multivariate analyses, it was possible to define hypotheses concerning the forces potentially regulating the bacterioplankton dynamics. During all the year, bacterioplankton appears to be highly influenced by physical factors such as temperature. Biotic top-down control or abiotic bottom-up control seems to play significant roles at some periods. To test the effect of these latter factors, in situ experiments were carried out. A synergistic, stimulating effect of added inorganic (ammonium and phosphate) and organic (glucose) was detected on biovolume and density indicating that bacterioplankton is nutrient-limited during clear water phase in the oligotrophic reservoir. On the other hand, biovolume increased when predators were removed indicating that bacterioplankton is somewhat top-down controlled during most productive periods in the meso- and eutrophic reservoirs.
Key words: bacteria, diversity, plankton, eutrophication