Leaf-Cutter Psychrometers: A Cautionary Note

Nontranspiring (covered) leaf water potential on greenhouse-grown chickpea (Cicer arietinum L.) leaves was measured with the pressure chamber and leaf-cutter psychrometer techniques over a range of water potentials. Potentials measured with the leaf-cutter psychrometer technique were highly variable and not well correlated with the values measured with the pressure chamber. The objectives of this study were to identify the basis for the discrepancy between the two techniques and to identify procedures to minimize the errors. Intentionally damaging 15% of the disc caused an increase (less negative) in the potentials measured in the psychrometers relative to those measured in the pressure chamber. When leaves were sampled with a sharp razor or a new biopsy punch, however, potential values similar to those measured by the pressure chamber were obtained. We conclude that unintentional damage caused by the psychrometer's cutter can give erroneous values of leaf water potential measured by leaf-cutter psychrometry.