Uptake and release of copper ions in epiphytic lichens

This study investigated the uptake and release of Cu ions in the epiphytic lichen Evernia prunastri, a species widely used to monitor trace metal pollution. A cross transplant experiment from a background area to a polluted one and then back to an unpolluted one was simulated by incubating lichen thalli with 10 and 100 mu M Cu2+ solutions and subsequently in deionized water to induce metal release. The working hypothesis was that after the accumulation of Cu ions, a forced release brings the concentration back to the original values. Copper treatment caused a significant uptake, proportional to the concentrations in the solution. Accumulation occurred mostly extracellularly (90% after incubation with Cu 10 mu M and 60% with Cu 100 mu M). The subsequent induced release was evident only in samples treated with 100 mu M, and was determined by the loss from intracellular compartments. Lichen vitality, expressed in terms of photosynthetic efficiency, was not affected by Cu treatment. It is concluded that while ionic uptake is a fast process, metal release requires a much longer time. In addition, it is confirmed that the cell wall is a buffer between the outer environment and the cell interior.