Influence of O2- and CO2-concentrations on oscillations in the transpiration rate from oat plants in darkness

The effect of changed O₂- and CO₂-concentrations in air on oscillations in the transpiration rate of young oat plants in darkness has been investigated. Lowering the O₂-concentration to 5% did not affect the oscillations. When the CO₂ in the air was removed, the transpiration rate increased, and the oscillations ceased. When the CO₂-concentration was raised to 0.3 or 3% the transpiration rate temporarily decreased, but the period of the oscillations was not changed. Further increase of the CO₂-concentration caused, after a temporary decrease, an increased transpiration rate, and the oscillations eventually ceased. The period of the oscillations was influenced by the temperature: a lower temperature gave a longer period. It is concluded that substomatal O₂-deficit or high CO₂-concentration do not play a crucial role in the origin of these oscillations.