Potassium uptake in the epiphytic lichen Hypogymnia physodes at concentrations and pH conditions as found in stemflow

Samples of the foliose epiphytic lichen Hypogymnia physodes were incubated with 0, 100, 500, and 1000 muM KCl solution for up to 120 min. K was absorbed by H. physodes only in single replicates of the most highly concentrated solutions. Otherwise a release of K of up to 26 mumol g(-1) d. wt. was observed. This can be attributed to the low affinity of K for the cation exchange sites in lichen cell walls. The K concentrations applied with the incubation medium correspond to concentrations found in stemflow from dieback-affected Picea abies forests in the Harz Mountains, northern Germany. The results suggest that stemflow is not a major source of K for H. physodes. The loss of K in the present experiment could be due to changes of the water content in the lichen thalli or due to membrane damage caused by S or heavy metals in the field.