Determination of the Parameters of Lichen Water Relations

Abstract

Lichens are poikilohydric, i.e. can lose most of the water from their thalli, and then recover metabolic activity when re-wetted. They share this feature with most bryophytes and many algae, but poikilohydry is absent from the vast majority of higher plants that are termed homoiohydric. Surprisingly little information is available on the basic water relations of lichens; only a few measurements of water potential and its components exist in the literature. water potential is an expression of the chemical potential or free energy status of water. It is a measure of the driving force that causes water to move into a system, or from one part of a system to another. It is only possible to measure the chemical potential of water in a given system relative to the chemical potential of pure, free water, i.e., of water containig no solutes and boun by no forces. We take the water potential of pure water to be zero under standars conditions of temperature and pressure.