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Assimilation and Respiration of Excised Leaves at High Concentrations of Carbon Dioxide

Robert Livingston and J. Franck
American Journal of Botany
Vol. 27, No. 7 (Jul., 1940), pp. 449-458
Stable URL: http://www.jstor.org/stable/2437080
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Assimilation and Respiration of Excised Leaves at High Concentrations of Carbon Dioxide
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Abstract

The photosynthesis and respiration of Hydrangea otaksa leaves are not completely inhibited by concentrations of carbon dioxide as high as 20 per cent. The effects of such high concentrations are strongly influenced by "internal factors," which are not directly controllable. The depression of the rate of assimilation by 20 per cent carbon dioxide is much greater during the dormant than the vegetative period. Physiologically young leaves are more tolerant of high concentrations than are old leaves. Their tolerance is increased by "sugar-feeding" and decreased by starving them. The rate of photosynthesis in 20 per cent carbon dioxide usually increases upon prolonged illumination. Leaves can frequently be induced to tolerate high concentrations of carbon dioxide by starting them in 2 or 5 per cent carbon dioxide and increasing the concentration by a series of small steps without interrupting the illumination. Leaves so conditioned assimilate in 20 per cent carbon dioxide at about half of their maximum rate. In one experiment, a leaf was conditioned to synthesize in 50 per cent carbon dioxide at about 15 per cent of its maximum rate. At constant intensity and for the range of concentrations studied, the conditioned rate is a linear function of the concentration of carbon dioxide. The depressant action of concentrated carbon dioxide is greater at high than at low light intensities. There is some evidence that a leaf which has been conditioned to high concentrations of carbon dioxide is less able than an ordinary leaf to photosynthesize at low concentrations. This effect occurs only after the leaf has been induced to assimilate rapidly in high concentrations of carbon dioxide; it is not produced by simple exposure to this medium.

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