SULPHUR DIOXIDE: ITS EFFECT ON PHOTO‐SYNTHETIC ¹⁴C FIXATION IN LICHENS AND SUGGESTED MECHANISMS OF PHYTOTOXICITY

Abstract

Summary The toxicity to lichens of dissolved sulphur dioxide (as measured by net photosynthetic 14C fixation) was studied as a function of pH and is linked with the oxidation‐reduction properties of sulphur dioxide. An examination of pigments from lichens and spinach exposed to aqueous sulphur dioxide in vivo and in vitro suggests that the increased toxicity observed at low pH values is associated in part with the destruction of chlorophyll by an irreversible oxidation process.

A Model for the Relationship Between Gaseous and Aqueous Concentrations of Sulphur Dioxide in Lichen Exposure Studies*

“…The biological correlation between the effects of aqueous and gaseous exposures established by Saunders (1966) on the basis of the work with Diplocarpon rosae Wolf spores is often referred to in lichen and other plant injury studies (Puckett et al, 1973;Hocking and Hocking, 1977;Tanaka, Takanashi and Yatazawa, 1974). Aqueous levels by this biological scale are considered to be a thousandfold less effective than gaseous concentrations.…”

Sulphur dioxide effects on fungi growing on leaf litter and agar media

“…Several vv'orkers have used different concentrations of dissolved SOj in liquid or semi-liquids whilst manipulating the different solubility products of SO, through alteration of pH (Puckett et al, 1973;Babich & Stotzky, 1980). In the experiment of , differential inhibition was concluded to be a selective effect of SO'^ on microorganisms, but the effective concentration of SOg in the presence of media containing carbohydrates was unknown.…”

Recovery of net photosynthesis and dark respiration on rehydration of the lichen, Cladina mitis, and the influence of prior exposure to sulphur dioxide while desiccated

“…Each of these phenomena, the dry deposition of SO.^ and the enhancement of NP activity on SO.ê xposure of hydrated lichen thalli, have previously been reported in separate experiments. Winner et al (1978) documented the sorption of gaseous SO.^ on desiccated lichen thalli, using sulphur isotopes to trace deposition patterns, while Puckett et al, (1973) observed enhanced rates of NP following exposure of hydrated thalli to SO.^ concentrations of 0-75 //I T'. Similarly Beekley & Hofiman (1981) found that short-term exposure of (hydrated) Parmelia bolliana thalli to SO2 concentrations of 001 //I L' enhanced rates of NP uptake by up to 25%.…”

“…It is interesting to note that although photosyntbetic rates were significantly enhanced in lichen samples they placed within the treatn-ient area, local populations were almost non-existent within this zone. Thus, while low level SOg exposure clearly results in short term stimulation of photosynthetic activity, underlying physiological responses, variously suggested to include the action of sulphite and bisulphite ions as reducing agents and uncoupling of electron transport from photophosphorylation (Puckett et al, 1973;Sheridan, Sanderson & Kerr, 1976), may ultimately prove detrimental to lichen populations.…”