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AME 33:53-66 (2003)
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Abstract
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Flow-cytometric mapping provides novel insights into the seasonal and vertical distributions of freshwater autotrophic picoplankton
Nicholas D. Crosbie1,2,*, Katrin Teubner1, Thomas Weisse1
1Institute for Limnology of the Austrian Academy of Sciences, Mondseestr. 9, Mondsee 5310, Austria
2Present address: Ocean Genome Legacy, 32 Tozer Road, Beverly, Massachusetts 01915, USA
*Email: nick.crosbie@oeaw.ac.at
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ABSTRACT: This is the first study using flow cytometry to characterize the population dynamics of freshwater autotrophic picoplankton (APP) over a full seasonal cycle, the goal of which was to accurately quantify and qualify the natural APP populations in
relation to major environmental parameters. In particular, we wanted to test current assumptions about the seasonal succession of prokaryotic and eukaryotic picoplankton cells, including the relationship between solitary picocyanobacteria and
microcolonies. Using flow cytometry, we were able to efficiently characterize the abundances of 4 lake APP assemblages in Lake Mondsee, including that of a solitary picocyanobacterial population exhibiting high 'side scatter' values. Such cells were not
readily enumerated by epifluorescence microscopy. Unlike Lakes Constance and Maggiore, we found no evidence of a spring peak in solitary picocyanobacteria--we propose that the lack of a spring peak in Lake Mondsee was due to weak stratification in
March-April and relatively deep vertical mixing. Since summer declines in the abundance of solitary picocyanobacteria were associated with extended periods of reduced light availability, it is likely that such declines were in part due to low relative
growth rates. Finally, we argue that the formation of microcolonies by picocyanobacteria is unlikely to be a strategy for more efficient nutrient recycling (e.g. Stockner & Antia 1986). Rather, we suggest that microcolonies reach high concentrations in
surface and near-surface waters due to the production of a photosynthate-rich mucilage resulting from active photosynthesis during periods of severe nutrient deficiency.
KEY WORDS: Microcolonies · Picocyanobacteria · Eukaryotic picoplankton · Flow cytometry · Sorting · Lakes · Calcite · Calcium carbonate
Full text in pdf format
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Published in AME Vol.
33, No. 1
(2003) on August 21
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2003
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