Response of in situ leaf psychrometer to cuticle removal by abrasion

In situ measurements of leaf water potential by thermocouple psychrometers are useful in monitoring the energy state of water in plants. Excessive equ ilibration times caused by low vapor conductance across the leaf cuticle an d vapor sorption in the psychrometer chamber often make in situ sampling di fficult. Several methods of removing the waxy leaf cuticle have been shown to increase water vapor conductance across the epidermis of the leaf, but t heir relative effectiveness has not been compared and equilibration times a re unknown. Six wax removal treatments were compared with an untreated cont rol to determine the most effective technique for increasing water vapor co nductance across the leaf surface. The mean time for the leaf psychrometer to reach an equilibrated water potential was estimated for the treatment th at produced the greatest conductance. Abrasion treatment of leaves with 600 grit sandpaper produced the greatest increase in cuticular conductance, re sulting in a mean equilibration time for psychrometer measurements of 7.5 m in.