Uptake of gaseous sulphur dioxide by the lichen Cladina rangiferina

Abstract

Samples of the lichen Cladina rangiferina were exposed to various concentrations of sulphur dioxide in a fumigation cuvette system for time periods ranging from 1 to 18 h. The cuvette system provided airstreams which, within the limits of measurement, had identical flow rates, temperatures, and relative humidities. Sulphur dioxide was added to one airstream as a treatment, while the other remained free of sulphur dioxide for control purposes. In some experiments, wind speed could be varied from 8 to 250 cm∙s−1 in a small wind tunnel placed in the fumigation cuvette. The system allowed for the calculation of sulphur dioxide uptake by the lichen sample. Potassium release was shown to increase with an increasing uptake of sulphur dioxide (time-integrated flux), but was not uniquely related to sulphur dioxide concentration alone. Extrapolation of a linear transformation of the potassium release curve to zero potassium efflux resulted in a threshold uptake value of 240 μg SO2∙g lichen−1. Internal lichen resistance and lichen boundary-layer resistance were experimentally determined for later use in an electrical analog model for the calculation of sulphur dioxide uptake.