摘要：The community structure and biomass of pelagic phototrophs, with particular attention to the picoplanktonic size fraction, were studied in a eutrophic Lake Strzeszyńskie in the Wielkopolska Lakeland (western Poland). Phototrophic community included prokaryotic cells, such as oxyphotobacteria (cyanobacteria), anoxyphotobacteria, eukaryotic cells representing cryptophytes, dinophytes, diatoms, chrysophytes, xanthophytes, haptophytes, and green algae. 112 taxa of the phototrophs were recorded. Most of them were eukaryotic cells (83 species), including chlorophytes (48) and diatoms (15). The range of the photortophs biomass was between 0.1 and about 3 mg l-1, and its maximum was at 8 m depth, mostly due to eukaryotic cells. In the shallower waters layers the contributions of the cyanobacteria and the eukaryotes to the total biomass were very similar. Starting from 10 m anoxyphotobacteria increased in importance and near the bottom their contribution to phototrophic biomass exceed 50%. The smallest phototrophs were dominated by the picocyanobacteria. The joint contribution of pico- and nanoplankton in the water column ranged significantly. In the epilimnion it was about 30%, in the upper part of metalimnion it reached 50%, and in the lower part of hypolimnion they accounted for 70% of total phototrophic biomass. In the microplankton, the highest biomass was produced by the filamentous cyanobacteria and phytoflagellates. These examinations are pointing out to the need for a holistic approach to the photosynthetic organisms and show that at increasing depths different groups of phototrophs play the role as major producers.
