The production of stress ethylene relative to the concentration of heavy metals and other elements in the lichen Hypogymnia physodes

The objective of this study was to examine fluctuations in the production of ethylene by the lichen Hypogymnia physodes indicative of environmental stress caused by air pollutants. In addition, we investigated the accumulation capacity of H. physodes, transplanted in the vicinity of two streets having slow traffic and a highway in the city of Oulu, N. Finland, for a short period (45 d). The amounts of stress ethylene produced by the transplanted lichens was compared with the amounts of airborne elements accumulated in the thallus. H. physodes manifested a high accumulation capacity for Fe and Mg in thalli exposed in either one or both streets with slow traffic in Oulu in comparison with thalli left on the control site in the forest outside of the city. Two of the observed elements, Zn and Fe, exhibited a significant positive correlation with the ethylene concentration detected concomitant with the treatment of lichen thalli with either H₂O (pH 6.8) or NaHSO₃ (pH 4.0). The concentrations of Pb, Fe, Zn, Mn, and Cu in thalli retrieved from one or both streets with slow traffic (13,600 and 14,290 cars/d) were higher than the concentrations in thalli transplanted in a highway with 25,240 cars/d after 45 d of exposure. Our data thus suggest that the streets with slow traffic and fewer cars are more polluted than the highway.