Photo-inhibition of phytoplankton photosynthesis as a function of exposure time |
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| Authors: | Masayuki Takahashi Sooji Shimura Yukuya Yamaguchi Yoshihiko Fujita |
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| Institution: | (1) Environmental Research Group, Fisheries Research Board of Canada, Biological Station, Nanaimo, B. C., Canada;(2) Department of Botany, Tokyo Kyoiku University, Otsuka, Tokyo, Japan;(3) Ocean Research Institute, University of Tokyo, Nakano, Tokyo, Japan |
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| Abstract: | The photo-inhibition of phytoplankton photosynthesis at higher intensities was examined with a cultured marine diatom,Phaeodactylum tricornutum, and natural samples. The question was to determine whether photo-inhibition results from excretion of photosynthetic products from cell or from an actual decrease in photosynthetic rate.
P. tricornutum cultured at 15 klux showed very little photo-inhibition up to 70 klux, and, in the sample cultured at 1 klux, most marked photo-inhibition was observed in 3 hours experiment. Extracellular release was less than 30% of particulate fixation, and did not show any extreme increase to supplement photosynthesis depression at higher light intensities. When the photosynthesis was measured during 10 minutes, both samples showed no photo-inhibition. The photosynthesis by low light sample lost the linearity of time-course with prolonged exposure at high light intensity. Observed photo-inhibition, therefore, we explained with the actual decrease in photosynthetic rate. Similar photo-inhibition could be seen in marine phytoplankton samples concentrated by filtration. |
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