Biomonitoring air pollution with the desert lichen Ramalina maciformis

To investigate the environmental impact of anthropogenic activity in the Negev Desert, we monitored the following in order to determine the physiological integrity of the epilithic fruticose lichen Ramalina maciformis: (1) production of ethylene; (2) potential quantum yield of photosystem II expressed as chlorophyll fluorescence ratio Fv/Fm; and (3) electrolyte leakage of cell membranes in terms of electric conductivity. The degree of pollution was assessed by measuring the amounts of B, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Sr and Zn in the lichen thallus. Some of the lichen-carrying stones collected in the relatively unpolluted control site were relocated on the same hill, to test the possible impact of relocation. An additional amount of lichen-carrying stones was marked as controls. The greater part of the lichen-carrying stones was transferred to 10 biomonitoring sites in and around Ramat Hovav, an industrial area in the Negev Desert, Israel. Transplanted lichen in polluted sites contained higher amounts of mineral elements than lichens in the control site after an exposure period of 7 months. Statistical analysis revealed positive correlation of ethylene production and Ni content, negative correlation of Fv/Fm ratios and B, Cu, Mn, Na, Ni, Sr and Zn, and positive correlation of electric conductivity and B, Mn, Ni and Sr. Both elemental content and physiological alterations in transferred samples of R. maciformis point to a high degree of contamination in Ramat Hovav. The present study suggests that the lichen R. maciformis should be classified as a sensitive species endangered by anthropogenic activity in the desert. Furthermore, this lichen species is likely to be suitable as a bioindicator of pollution in other parts of the Negev Desert. Ethylene production and electric conductivity as parameters of lichen-vitality, indicated stress in 5 of the 12 biomonitoring sites (42%) and may therefore be considered as more sensitive than the Fv/Fm ratio, which indicated stress in 3 of the 12 sites (25%).