Effects of light intensity on photosynthesis and dark respiration in six species of marine phytoplankton
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Using an oxygen polarographic electrode, the shapes of photosynthetic curves and the effects of light on dark respiration in 6 species of marine phytoplankton wer examined. The species used were Skeletonema costatum, Ditylum brightwellii, Cyclotella nana (Thalassiosira pseudonana) (all Bacillariophyceae), Dunaliella tertiolecta (Chlorophyceae), Isochrysis galbana (Haptophyceae), and Gonyaulax tamarensis (Dinophyceae). A hysteresis was observed in all species examined with respect to increasing and decreasing light. Compensation light intensities varied by over 4 orders of magnitude, suggesting that the 1% light depth is an ambiguous measure of the euphotic zone. The data suggest that dark respiration accounts for ca. 25% of gross photosynthesis, but is species-dependent. In addition, respiration versus cell size does not describe an inverse exponential function over the size scales examined.
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