Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoir

Abstract

Summary We investigated net growth rates of distinct bacteri- oplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus avail- ability by analysing eight in situ manipulation experi- ments, conducted between 1997 and 2003, in the canyon-shaped ímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phos- phorus limitation (range of soluble reactive phospho- rus concentrations - SRP, 0.7-96 m g l - 1 ). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate con- stants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates S ˇ n ˇ rˇ s ˇ C ˇ e ˇ C ˇ e ˇ R ˇ mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betapro- teobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabili- ties for possible life strategies of different bacterial phylogenetic lineages are discussed.