The effects of sulphur dioxide on net CO sub(2) assimilation in the lichen Evernia mesomorpha) Nyl

Physiologically active thalli of the lichen Evernia mesomorpha Nyl. were very sensitive to short-term fumigations with low concentrations of gaseous sulphur dioxide. Net CO sub(2) assimilation rate (NAR) was significantly reduced after exposure to SO sub(2) for 1 h or more, and the reduction increased with increasing concentration. Duration of exposure had no significant effect on NAR, indicating the importance of rate of SO sub(2) uptake rather than the total amount absorbed. Based on this study, neither the concept of dose (concentration x time) nor that of "threshold" levels of SO sub(2) fumigations are supported. Peak exposures to SO sub(2) for short periods may be of primary importance in determining the survival of lichens in industrial areas.