Matric Water Potential of Leaf Tissue—Measurement and Significance

Abstract

A thermocouple psychrometer method, previously described for use in determining tissue and sap water potentials, has been adapted for determining matric potentials. Matric values ranging from approximately zero to −10 × 105 Pa were observed with wilting wheat leaves. Mean values of total tissue water potential and of its solute (osmotic), matric, and cell wall pressure components were −16.6, −18.3, −30 and +4.7 Pa × 105, respectively. Matric potentials are often ignored in investigations of plant water relations. This practice is shown to result in underestimation of wall pressures (in this case by a mean of 64 per cent) and sometimes in spuriously negative values.