Some Aspects of the Water Relations of Lichens from Habitats of Contrasting Water Status studied using Thermocouple Psychrometry

Thermocouple psychrometry was used to investigate the water relations of eight species of lichens from sites of contrasting water status. Lichens from exposed, dry habitats had lower thallus K concentrations but lower osmotic potentials than plants from mesic sites. As a result, K contributed a much smaller proportion to osmotic potential in plants from dry sites, suggesting that low cytoplasmic K concentrations are important for desiccation tolerance. While containing less water at saturation, plants from dry habitats had lower thallus elastic moduli and lower apoplastic water fractions. They therefore lost turgor at lower relative water contents than plants from wetter sites. The significance of these results for the water relations of lichens is discussed.