Stomatal aperture oscillations of Abutilon theophrasti Medic. and Hordeum vulgare L. examined by three techniques.

Temporal fluctuations of stomatal aperture are important to water use efficiency. Techniques that use point measurements widely spaced in time such as diffusive resistance porometry (DRP) or pot weighing (PW) may not provide a complete description of changes in stomatal aperture. Three techniques, DRP, PW, and continuous flow porometry (CFP), were used to examine stomatal aperture changes in Hordeum vulgare L. and Abutilon theophrasti Medic. Plants maintained in controlled environment chambers at 23 degrees C under LD 12:12 were monitored during 2 days of continuous illumination (LL) and a subsequent LD cycle. Oscillations with periods of about 24 hr were observed in both leaf surfaces in the two species. In addition, during LL, high-frequency fluctuations were sometimes superimposed on the 24-hr oscillation. There was better agreement between the results of CFP and DRP in Abutilon than in Hordeum. The reason for this difference is unclear. CFP revealed rapid fluctuations in stomatal aperture that were not observed with the other techniques.