Longitudinal changes in protistan bacterivory and bacteria production in two canyon-shaped reservoirs of different trophic status

摘要

We studied bactrialproduction and mortality due to heterotrophic nanoflagellate(HNF) and cilicate grazing on longitudinal transects conducted on two canyon-shaped reservoirs of different trophic status,Rimov and Orlik (Czech republic).Special attention was paid to the changes in these processes related to depth,spatial distribution of sampling points,different of planktonic succession and to the taxon-specific bacterivory of cilicates.Bacterial production (BP) in obht reservoirs was,on average,reaching similar values (ranging from 1.2 X 10~6 to 4 X 10~6 bacteria ml~-1d~-1).In Rimov (mesoeutrophic,mean retention time 100 days),when seasonally averaged,total protistan grazing accounted for 35% of BP and was consistantly lower in the layer R(layer with the same temperature and conductivity as the river inflow).On the contrary,the seasonal average for the Orlik reservoir (eutrophic,mean retention time of 23 days) showed roughly two times higher proportion of BP (70% of the total) removed by protists.In both reservoirs,there was little or no difference in contribution of ciliates and HNF to total protistan bacterivory.Overall,oligotrichous cilicates bacterivory in Rimov and Orlik,respectiely) followed by peritrichous ciliates that contributed to total ciliate bactrivory from 23%(Rimov) to 28%(Orlik).A small omnivorous oligotrichous ciliate Halteria cf.grandinella was the major bacterivore within the whole ciliate community in both reservoirs,contributing as much as 48 and 34% to the total ciliate bacterivory,in the Rimov and Orlik reservoirs,respectively.