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A survey of the adaptation of plankton algae in Nature to different light intensities and temperatures is given. The adaptation is always important for the plankton populations at all depths. However, the shade adaptation of the algae in the lower part of the photic zone is often of relatively little importance for the integral primary production per unit of surface, except on the by no means rare occasions when the hulk of the algae is found in this lower part. It is shown that the Ik of surface plankton during summer in the Arctic is high despite the low temperatures present. This is due to an increase of the enzyme quantities per cell. Daily fluctuations in Ik are due partly to photooxidation, partly to the fact that the periods for the production of chlorophyll and photosynthetic enzymes are mutually displaced. Despite the daily fluctuations in Ik the difference between "sun" phytoplankton and "shade" phytoplankton is distinct. [ABSTRACT FROM AUTHOR]

The theory that Skeletonema cells adapt to lower temperatures by increasing their enzyme concentration, is supported by various facts. While the rates of photo- synthesis are identical in cells adapted to different temperatures (7-20°C) the growth rate decreases with decreasing temperature and the production of organic matter increases with decreasing temperature. Further, the concentration of protein per cell and the height of the cells increase with decreasing temperature. [ABSTRACT FROM AUTHOR]

Filtered culture solutions from cultures of different unicellular algae, especially Chlorella vulgaris, were tested for content of growth affecting substances using the bacteria Staphylococcus aureus as test organism. Either a decrease or an increase of the growth of the bacteria could be found. It was observed that both growth accelerating and growth inhibiting substances were present simultaneously in the culture solution and that the concentration of the substances varies a great deal in cultures of the same algal species even if the cultures were grown under apparently identical conditions. In one of the experiments the inhibiting effect was decreased by heating the algal filtrate at 70°C for 20 min. In another experiment at least two inhibitors were found. One was inactivated by illumination of the algal filtrate, a second was absorbed to Norit. [ABSTRACT FROM AUTHOR]

Experiments were carried out with algae in mixed cultures (two species cultures) or with algae cultured in filtrates from cultures of other algae or the same species. In experiments with Asterionella formosa and Nitzschia palea it was shown that both species formed substances which inhibited the growth of the other species and that the rate of inhibition was very dependant on the experimental circumstances. It was shown further that Nitzschia formed autotoxic substances and it was suggested that Asterionella formed substances which accelerated the growth of other Asterionella cells and of Nitzschia in some cases. In experiments where Nitzschia was cultured in filtrates from Scenedesmus quadricauda and Chlorella pyrenoidosa cultures, it was shown that Scenedesmus formed substances which considerably inhibited the growth of Nitzschia. The growth of Nitzschia was not inhibited in filtrates from a 4-8 days old Chlorella culture but was distinctly so in filtrates from a 13-17 days old Chlorella culture. When Chlorella was cultured for 3 days in filtrates from a 21 days old Scenedesmus culture a marked inhibition of the growth was found. During 3 days of culturing of Chlorella in filtrate from a 21 days old Nitzschia culture an acceleration of the growth of Chlorella took place. Similarly an inhibition of the growth was found when Scenedesmus was cultured for 3 days in filtrates from a 21 days old Scenedesmus culture. On the other band, an acceleration of the growth of Scenedesmus took place when it was cultured in filtrates from a 21 days old Chlorella and a 21 days old Nitzschia culture, respectively. [ABSTRACT FROM AUTHOR]

Experiments carried out with the diatoms Nitzschia linearis and Thalassiosira nana show that the silicon in the cell walls is soluble in water and that the rate of solubility depends on the pH of the solution. The rate increases with increasing pH. At pH 8 not much more than 5 per cent of the silicon in the cells was dissolved in both species during the experiments, at pH 10 Thalassiosira was dissolved completely. In the case of Nitzschia linearis 20 per cent of the silicon was dissolved at pH 10 during the experiment. Thus the silicon compounds are found in the diatom cells in forms which arc hydrolyzed at different rates. The silicon compounds in Thalassiosira are easy to hydrolyze at pH 10. In Nitzschia linearis some parts are easy to hydrolyze, others very difficult. [ABSTRACT FROM AUTHOR]

Investigations of the plankton diatoms in lakes and planktonic and epiphytic diatoms in cultures have shown that the silica content in the cells depends on the number of cells, and the silica content is inversely proportional to the number of cells. This is the case both in ordinary cultures where the Si-concentration and the concentration of other nutrient salts are decreasing when the number of cells increase and in cultures with a flowing culture solution. The decrease in the silica content is probably caused by diatoms giving off a substance to the water which inactivates the silica assimilation. [ABSTRACT FROM AUTHOR]

Two experiments with Nitzschia palea and with Bacillaria paradoxa, respectively, are described. The diatoms were cultivated in plastic containers of polystyrene. In each experiment three series with different initial Si-concentrations were carried out (0.3, 1.8, and 5.3 mg Si and 0.8, 1.8, and 5.8 mg Si per liter). 24 containers in each series were used. The growth was determined by the increase in chlorophyll content, in some cases also by the number of cells. The Si-concentrations were determined during the experiments with the methods described. In both experiments the Si-concentration decreased rapidly to a level of 30- 40 μg Si per liter independently of the initial Si-concentration, and then further uptake took place only very slowly. In Experiment 1 concentrations down to 15-20 μg Si and in Experiment 2 down to 5(0)--10 μg Si per liter were found at the termination of the experiments. The growth of Nitzschia palea (increase of chlorophyll content and number of cells) stopped or nearly stopped when the Si-concentration of 30-40 ug Si per 1 was reached. The same was the case in Experiment 2 with Bacillaria paradoxa concerning the increase of number of cells, but in this experiment on the other hand the increase in chlorophyll content continued to the termination of the experiment. Through investigations in some Danish eutrophic lakes the author found that the Si-concentration decreases to a similar level as found in the experiments, 30-40 μg Si per liter during the diatom maxima. [ABSTRACT FROM AUTHOR]