SOME ASPECTS OF THE WATER RELATIONS OF THE LICHEN PARMOTREMA-TINCTORUM MEASURED USING THERMOCOUPLE PSYCHROMETRY

The thermocouple psychrometer was used to determine water potential, p si, and its components in the lichen Parmotrema tinctorum. Data sugges ted that using conventional pressure-volume curves to study the water relations of lichens may give anomalous results, possibly because lich ens may contain appreciable amounts of intercellular water. A way of c orrecting pressure-volume curves to remove the effect of intercellular water is discussed. Parmotrema tinctorum had a very low osmotic poten tial at full turgor (c. - 2.5 MPa), and a low bulk modulus of elastici ty (c. 2.1 MPa). As a result, P. tinctorum lost turgor only when the r elative water content dropped below 0.47. Likely benefits of this for the lichen are discussed. (C) 1996 The British Lichen Society.