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Summary
After an ecological study of Oscillatoria rubescens D. C. in the lake of Nantua, the authors present here an in-vitro study of this blue-green alga. A 8 units battery of chemostats, Staub's axenic strain and ASMI, Gorham's medium, diluted 5 times, were used in this purpose.
In the first experiments described, a slight contamination appear in most chemostats. New exenic experiments are in progress and first conclusions had been controlled.
Production of 100 mg dry matter, correspond to consumption of about 5 mg of nitric-nitrogen and to consumption of about 0.5 mg of orthophosphoric-phosphorus. Most of our chemostats were limited (Liebig law) by nitrogen. Maximal observed growth rate was of 0.53−1 and was higher than indirect calculated maximal growth rate: 0.47−1.
Our conclusions are in agreement with Droop's one: the amount of the limiting nutrient in the cells controls the rate of growth. But we found that it controls also the amount of non limiting nutrients present in the cells. In condition of severe limitation, when the limiting nutrient drops to zero in the outflowing medium, the rate of growth is governed by the flow of limiting nutrient coming to the cells. These conditions are probably similar to those appearing in an eutrophic lake like Nantua, with permanent inflow of sewage.
Alcaline phosphatase activity seems permanent, but increases with lowering flow of phosphates. It is the total phosphorus cell quota, and not the hot water extractable phosphorus which controls phosphatase activity.
Measurement of cell quota in phytoplankton with a dominant species (like a water bloom) must be a valuable tool for the ecologist.