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Lobelia dortmanna L. is probably unable to utilize HCO3- and uses only free CO2 for photosynthesis as shown by the Winkler method. A 14C technique was used to show that if CO2 is added to the water around roots, photosynthesis increases 3-5 times more than when the corresponding amount of CO2 is added to the water surroundings the leaves. As the CO2 content in lakes where Lobelia grows is very limited, Lobelia must absorb CO2 from the sediment, and the carbon dioxide will have to diffuse from the roots up into the leaves through the intercellular system of the plant. In conjunction with Lobelia's CO2 uptake from the sediment O2 is liberated. The plant, therefore, acts as an oxygen pump, which oxidizes the sediment down to a depth of 20 cm. [ABSTRACT FROM AUTHOR]

Cu in ionic form in a balanced medium affects the rate of photosynthesis and growth in the diatom Nitzschia palea in about the same way as in the green alga Chlorella pyrenoidosa. Remarkable differences are found, however. Small concentrations of Cu influence the rate of photosynthesis considerably more in the diatom than in the green alga whereas the opposite is the case concerning growth. The latter is most likely a consequence of excretion of organic matter by the diatom in presence of Cu whereas this does not take place in Chlorella. Some of the excreted organic matter may bind Cu and thus make the medium suitable for growth. Although pre‐treatment with Cu in the dark has no influence on the subsequent rate of photosynthesis in the light, organic matter is excreted in the dark immediately after the addition of Cu. The influence of Cu on the rate of photosynthesis varies by a factor of about 30 according to the stage of growth in a synchronized culture. [ABSTRACT FROM AUTHOR]

If a single salt solution of CuSO4 is used, Cu penetrates immediately into the plasma of Chlorella cells, reducing the rates of photosynthesis at both high and low illumination. If CuSO4 is added to ordinary Österlind culture-medium (pH 8) it takes some hours before any influence of deleterious concentrations of Cu is observed and initially only at light saturation. The algae must have been illuminated during the whole period. Maximum influence of CuSO4 is found during the first 24 hours of treatment. A significant deleterious influence of Cu concentrations as low as about 1 μg/l is found. The influence of Cu increases with decreasing concentrations of the alga. If a culture medium at pH 5 is used instead of the ordinary one at pH 8, copper concentrations about 10 times as high must be used in order to obtain the same deleterious effect. An increase of the concentration of K reduces the influence of Cu to some extent. These facts show that the effect of deleterious concentrations of Cu in balanced solutions is not due to a marked penetration of this ion into the plasma but to a binding to the cytoplasmic membrane whereby the cells i.a. become more or less unable to divide. The cells become saturated with assimilation products which have a depressant effect on the rate of photosynthesis. Other cations compete with Cu for the "active sites" on the membranes. [ABSTRACT FROM AUTHOR]