THE EFFECT OF TIME OF EXPOSURE TO SULPHUR DIOXIDE ON POTASSIUM LOSS FROM AND PHOTOSYNTHESIS IN THE LICHEN, CLADINA RANGIFERINA (L.) HARM.

Abstract

SUMMARYSamples of the lichen, Cladina rangiferina., were exposed to various concentrations of aqueous SO2 for 10 min, and 0.5, 1, 3, 6 and 12 h. K*-efflux curves (K* release versus ppm SO2 (wt/wt, aqueous)) were constructed for each exposure period. In separate experiments, the photosynthetic ' "^C fixation rates were measured after the SO2 exposures. Plots of % total ^^C fixation v. ppm SO2 (wt/wt, aqueous) were found to be linear for the 3 h and 6 h exposure periods, while plots of log (% total ^'C fixation) v. ppm SO2 (wt/wt, aqueous) were linear for shorter exposures (10 min, 0.5 and 1 h). Threshold SO2 concentrations for each exposure time were evaluated by extrapolating the K' *"-efflux curves, or their linear transformations, to zero K"*" release. Similarly, the threshold SO2 concentrations that did not cause a reduction in ^"^C fixation (relative to control samples not exposed to SO2) were determined by extrapolation of the linear relationships mentioned. The threshold values obtained from the K"^-efflux data were in good agreement with those evaluated from fixation rates. Aqueous threshold SO2 concentrations were converted to gaseous threshold values by an experimentally verified relationship. The resulting gaseous SO2 threshold concentrations, (S02)g* in units of ppm (v/v) in air, were related to the exposure time in hours, t, through the following rectangular hyperbolic function: (S02)g* = 1.5 t~^'^^. Notwithstanding the uncertainties involved, extrapolation of this expression to exposure times considerably longer than the experimental range yielded threshold values for 6 months and 1 year in good agreement with mean SO2 levels known from mapping studies to affect detrimentally sensitive lichen species.

Lichens and Particulate Matter: Inter-relations and Biomonitoring with Lichens

“…As the opposite situation was apparent, it is suggested that large amounts of trace metals accumulating in the lichens result in the removal of 137 Cs. Several studies demonstrated an enlarged loss of potassium following an exposure of lichens to trace elements (Puckett 1976;Nieboer et al 1979;Tarhanen et al 1999;Hyvärinen et al 2000;Cabral 2003;Mrak et al 2007) or to SO 2 Tomassini et al 1977). Low K contents were observed also for lichens in environments polluted by trace metals and other contaminants (Garty et al , 1997c(Garty et al , 1998a(Garty et al , 2002cAdamo et al 2003;Williamson et al 2004;Tretiach et al 2007).…”

Potassium Efflux by Lichen Thalli Following Exposure to Aqueous Sulphur Dioxide*

“…Although the K"*" efflux rate increased with the total available SO2 per unit weight of lichen, the x-intercept of extrapolations, and hence evaluated sensitivity, was only minimally affected. This aspect is considered in more detail by Tomassini et al (1977). Table 1 shows that K"^ loss during a 3 h exposure was induced in sensitive species by equivalent gaseous concentrations less than 1 ppm while other species were unaffected by levels in excess of 2 ppm for this period.…”

Biomonitoring air pollution with the desert lichen Ramalina maciformis

“…Controlled experiments investigating the effect of exposure to SO 2 were described by Puckett et al. (1977) and Tomassini et al. (1977).…”