Seasonal variations in tolerance to ion leakage following desiccation in the moss Atrichum androgynum from a KwaZulu-Natal afromontane forest

A simple ion leakage assay was used to test if seasonal variation in changes in membrane permeability in response to desiccation occurs in a single population of the moss Atrichum androgynum. ion leakage following rewetting of dry plants was measured at monthly intervals from the end of a wet season, throughout a dry season and at the beginning of the next wet season. At the end of the first wet season, plants pretreated for 24 h at relative humidities of 0% or 53% lost c. 80% of their intracellular K+ following rewetting. The proportion of K+ lost progressively declined until by the end of the dry season plants lost less than 25%. After the start of the second wet season K+ toss increased. Thallus K+ concentrations fell slightly during the experimental period, white the osmotic potential at full turgor (psi(pi s)) decreased from -0.75 to -1.20 MPa. However, the increase in sensitivity at the start of the second wet season was not accompanied by a rise in psi(pi s) suggesting that no simple relationship exists between the susceptibility of plants to ion leakage and psi(pi s).