Threshold Value of Carbon Dioxide Concentration in Photosynthesis of Foliage Leaves

Abstract

How much can the carbon dioxide concentration of the atmosphere be diminished by photosynthesis of green leaves? Blackman¹, in his researches in vegetable assimilation and respiration, observed that leaves exposed to sunlight took up completely all the carbon dioxide molecules from an enclosed volume of air in a very short time. Reinau² did not accept this result which, he thought, was caused by some experimental error. He concluded, entirely on the basis of theoretical considerations, that the carbon dioxide concentration of the atmosphere (mean value 0.030 vol. per cent) could be lowered only very slightly by the photosynthetic activity of leaves. Later, in 1935, the problem was investigated by Miller and Burr³, who placed potted greenhouse plants in a chamber inside a closed system through which a vigorous circulation of air was maintained. When the leaves were illuminated with 2,050 foot-candles, they found that the carbon dioxide concentration in no case (thirty-four plants from ten species were employed) could be brought below 0-010 vol. per cent.