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. Potential s 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 discrepan cy between the two techniques and to identify procedures to minimize the er rors. Intentionally damaging 15% of the disc caused an increase (less negat ive) in the potentials measured in the psychrometers relative to those meas ured in the pressure chamber. When leaves were sampled with a sharp razor o r a new biopsy punch, however, potential values similar to those measured b y the pressure chamber were obtained. We conclude that unintentional damage caused by the psychrometer's cutter can give erroneous values of leaf wate r potential measured by leaf-cutter psychrometry.