Two parameters were applied to estimate the degree of stress induced by exposure of the lichen Ramalina duriaei (De Not.) Bagl. to air pollution in urban-industrial sites in Israel. Changes in the spectral reflectance response of the thallus and in the production of stress-ethylene, were compared with the concentration of sulphate-S, V, Ni, K, Pb, P, Cu, Cr, Fe, Mn and Mg in either in situ or in transplanted thalli of the lichen.

The concentrations of Cu, Mg, Fe, Ni, Pb, V, Cr, Mn and sulphate-S in in situ thalli collected in a nature reserve in an industrial town (Ashdod, SW Israel) were higher than those detected in in situ thalli collected in a forest (HaZorea Forest) in the north-east of Israel. The high concentrations of these mineral elements in R. duriaei from the nature reserve coincided with a high rate of production of stress-ethylene and with a low normalized difference vegetation index (NDVI) indicating that changes in the spectral reflectance response relate to damage to the chlorophyll.

Lichens collected in the unpolluted forest in February 1994, either resuspended in the same site or transplanted in nine sites in the Ashdod region, and retrieved in November of the same year, contained a higher concentration of sulphate-S, Pb, Cu, Ni, V and Cr in the urban-industrial sites than in most of the rural localities. Statistical analysis revealed a positive correlation between the amount of ethylene produced by R. duriaei and the concentration of V and Ni in the same thalli.

To test the integrity of the ethylene-producing system, lichens were soaked in either 5 mM or 10 mM FeCl2 at pH 3·7. Thalli exposed to a very polluted environment produced less ethylene after this treatment. The NDVI correlated positively with the concentration of K in the thallus but negatively with the concentration of Mn, Ni, Pb and sulphate-S in the same material.

It may be concluded that the in situ thalli of R. duriaei in the nature reserve are severely stressed and possibly endangered by the pollution produced by the combustion of heavy fuel oil in the local power plant and oil refineries and by acid rain.