Some notes concerning the measurement of water potentials of leaf tissue with specific reference to Tsuga canadensis and Picea abies

Psychrometric measurements of the water potentials of leaves of Tsuga canadensis (L.) Carr. and Picea abies L. are compared with the water potentials of the shoots from which they came as measured by the pressure-bomb technique. Agreement between the two techniques is good when whole leaves are used in the psychrometer chamber, but deviations occur when bisected leaves are used in which the wound area to tissue volume is very small (1 to 2 cm2/cm3 of leaf tissue). Psychrometer determinations of water potential of these detached leaves are much more sensitive to cutting than in other species, e.g., sunflower and pepper (2). A more reliable means of measuring turgor and osmotic pressures in leaves is proposed.