Rôle du bactérioplancton en milieu lacustre pélagique : prépondérance des plus grosses bactéries

Abstract

Bacterioplankton abundance (AB), heterotrophic production (PB) (thymidine incorporation) and renewal time (tr = AB/PB) were determined in eight Canadian Shield lakes in two size classes of bacteria (< 1 μm and > 1 μm). Although large bacteria (> 1 μm) were often less than 50% in numbers, they produced most of the new cells in 20 out of 21 trials. Large bacteria had a tr shorter than that of small ones (< 1 μm). Large bacteria not only represent much of the biomass, but seem to be the principal site of carbon and energy flow within the bacterial community. There was a significant positive correlation between PB of the whole bacterial community and primary production (PP), but we found no correlation between PB and chlorophyll a concentration (CHL). Similar results were obtained for the large bacteria. On the opposite, we found no correlation between PB of the small bacteria and PP, but a significant positive correlation between PB and CHL. Only the small bacteria showed a significant correlation between PB and AB, as well as a more constant rate of reproduction. Our results modify the importance of AB values found in the literature, give a good reason for the weak correlation between PB and AB found in other studies, and change the generally accepted scheme of organic and energy flow in planktonic systems. Key words: bacterioplankton, size class, productivity, correlation.