Effects of Sulfur Dioxide Fumigation on Photosynthesis, Respiration, and Chlorophyll Content of Selected Lichens

Abstract

Four lichens-Parmelia bolliana Mull. Arg., Physcia stellaris (L.) Nyl., Xanthoria fallax (Hepp) Am., and Physconia grisea (Lam.) Poelt--listed in order of decreasing mesophytism, were fumigated for 4 hr at 0.01, 0.1, 1.0, and 2.5 ppm sulfur dioxide to determine the effects on photosynthesis, respiration, and chlorophyll content. The lichens had been collected from Populus deltoides Marsh or Tilia americana L. in northeastern South Dakota near a lignite-fired power generator. Photosynthesis decreased after fumigation at 1.0 and 2.5 ppm, but significant decreases occurred only after fumigation at 2.5 ppm. Expressed on the basis of per unit weight chlorophyll content, photosynthesis of Physconia grisea was most sensitive followed by that of Xanthoria fallax, Physcia stellaris and Parmelia bolliana. Expressed on the basis of per unit dry weight of lichen sample, photosynthesis of Physconia grisea was most sensitive followed by Xanthoria fal- lax, Physcia stellaris, and Parmelia bolliana. In both cases, the more xerophytic species were more sensitive. Chlorophyll content in these species was not mea- surably altered by fumigation. Comparison of chlorophyll a and b absorption spec- tra peaks for fumigated and control samples indicated that no phaeophytinisation occurred. Insignificant and inconsistent differences in chlorophyll a/b ratios were observed. Respiration of Physcia stellaris and Parmelia bolliana decreased signif- icantly following fumigation with 2.5 ppm S02; both species were more sensitive than Xanthoria fallax. Physconia grisea was not tested for respiratory responses. The effects of S02 fumigation on measured metabolic rates differed with the species. Photosynthetic rates of the xerophytic Xanthoria fallax and Physconia grisea were more sensitive than the more mesophytic Parmelia bolliana and Phy- scia stellaris. In contrast, respiratory sensitivities to S02fumigation were greater for P. bolliana and P. stellaris. It is well known that lichens are sensitive to air pollution, particularly to sulfur dioxide. Field studies from a variety of locations have reported evidence of the phytotoxicity of sulfur dioxide. Hawksworth's (1971) review of the literature is comprehensive; studies done since 1971 have left his basic conclusions unchanged. Experimental studies to examine the basis of lichen sensitivity have produced inter- esting results, which in some cases are not altogether consistent with field observations. Summaries of experimental studies have been presented by Gilbert (1973) and Nieboer et al. (1976). Experimentally, lichens have been exposed to both low and high concentrations of sulfur dioxide. In studying the effects of exposure on photosynthesis, Pearson & Skye (1965) used concentrations ranging from 102 ppm to 105 ppm. Puckett et al. (1973) used