JOURNAL OF PLANKTON RESEARCH | VOLUME 19 | NUMBER 8 | PAGES 979-993 | 1997
© Oxford University Press
research-article |
Seasonal photosynthetic activity of autotrophic picoplankton in Lake Kinneret, Israel
1Israel Oceanographic and Limnological Research, The Yigal Allon Kinneret Limnological Laboratory PO Box 345, Tiberias, 14102, Israel 2Bar-llan University, Department of Life Sciences Ramat-Gan, Israel
Received on August 3, 1996; accepted on March 26, 1997
Autotrophic picoplankton populations in Lake Kinneret are composed of picocyanobacteria and picoeukaryotes. Overall, the rates of photosynthetic carbon fixed by autotrophic picoplankton during this study were low (0.011.5 mg Cm3 h1). The highest chlorophyll photosynthetic activity of the <3 µm cell-size fraction was found in spring, when picoeukaryotes predominated and in addition small nanoplankton passed through the filters. The maximum cell-specific photosynthetic rate of carbon fixation by picocyanobacteria and picoeukaryotes was 2.5 and 63 fg C cell1 h1, respectively. The highest specific carbon fixation rate of autotrophic picoplankton was 11 µg C µg1 Chl h1 The proportional contribution of autotrophic picoplankton to total photosynthesis usually increased with depth. Picocyanobacteria collected from the dark, anaerobic hypolimnion were viable and capable of active photosynthesis when incubated at water depths within the euphotic zone. Maximum rates of photosynthesis (Pmax) for picocyanobacteria ranged from 5.4 to 31.4 fg C cell1 h1 with the highest values in hypolimnetic samples exposed to irradiance. Photosynthetic efficiency (
) was
4- fold higher in picocyanobacteria sampled from 40 m than in cells from near-surface waters. Light saturation (Ik) was lower in picocyanobacteria from 40 m, suggesting that these cells were acclimated to lower light intensities. The relative contribution of autotrophic picoplankton to total phytoplankton photosynthesis in Lake Kinneret was low, but occasionally, at seasons and depths where picocyanobacteria or picoeukaryotes were abundant, could account for most of photosynthetic activity.
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