Nonsynchronized Oscillations in Stomatal Resistance among Sclerophylls of Eucalyptus umbra.

Oscillations in stomatal resistance to viscous air flow have been recorded in the juvenile and adult sclerophylls of Eucalyptus umbra R. T. Baker, in both controlled and natural environments. Under constant illumination, temperature, and humidity, irregular oscillations in stomatal resistance with a periodicity of approximately 20 to 30 minutes occurred spontaneously, when the soil water potential was approximately -0.2 bar. In the natural summer environment, similar stomatal oscillations developed with periods ranging from 60 to 100 minutes only after imposition of soil moisture stress equivalent to -2 to -3 bars water potential. These cycles in stomatal resistance were not synchronized among the leaves of a given plant in any of the experiments.