The Interrelation between CO2 Metabolism and Photoperiodism in Kalanchoë.

Abstract

The diurnal CO2 metabolism of Kalanchoe blossfeldiana, was studied under long days, short days, and short days with interrupted nights. NaOH absorption towers and an infra red gas analyzer were used for determining CO2 A gas-tight chamber is described which encloses only the shoot portion of rooted plants, and enables their study in complete gaseous isolation from the roots. With this apparatus the dark uptake of CO2 by succulent plants reported by other workers is confirmed for Kalanchoe. It is shown, however, that exposure to repeated short-day cycles increases both the amount and the rate of the net dark fixation of CO2. The fixation passes through a maximum and may be followed by a brief period of CO2 production before the end of the dark period. If the plants are kept in darkness after 16 hours, a steady loss of CO2 by respiration takes place and continues at a nearly constant level. Exposure to repeated short days also causes a burst of CO2 on illumination; the amount of CO2 evolved parallels the amount absorbed during the preceding dark period. This CO2 burst also occurs, though only to a very small extent, in plants kept in long days. The two phenomena, i.e., the dark fixation 6f CO2 and the CO2 production in light, are ascribed to the destruction by light or high temperature of a substance, probably an organic acid, produced by CO2 fixation in the previous dark period. This photo- or thermo-labile substance is not metabolized away in 48 hours of darkness, but appears to require illumination, high temperature, or both, for its destruction. Interrupting a long dark period at its midpoint with 10 minutes of light completely inhibits the dark fixation of CO2 and also the associated CO2 production on illumination. Various mechanisms to account for the results obtained are critically discussed, and a possible relationship is suggested with the photoperiodic induction of flowering.