THE EFFECT OF CU, ZN AND PB ON THE CHLOROPHYLL CONTENT OF THE LICHENSCLADONIA-CONVOLUTA AND CLADONIA-RANGIFORMIS

It was hypothesised that Cu was responsible for the reduced chlorophyl l content of lichens growing in mining areas in which Cu, Zn, and Pb w ere present in the soil. Therefore, the effect of Cu, Zn, and Pb, indi vidually and in combination, on the respective thallus metal content o f the lichens Cladonia convoluta and Cladonia rangiformis, and the sub sequent effect on chlorophyll content, were examined. Increasing liche n Cu content (up to 1600 mu g g(-1) dry weight (DW)) had no effect on the total chlorophyll content of C. rangiformis, whereas in C. convolu ta Cu concentrations exceeding 175 mu g g(-1) DW caused a decrease in total chlorophyll content, which was 40% at 1560 mu g Cu g(-1) DW. Lic hen Zn and Pb concentrations of up to 1050 and 3350 mu g g(-1) DW for C. convoluta and 1210 and 8500 mu g g-L DW for C. rangiformis, respect ively, had no effect on the total chlorophyll content of either lichen . The chlorophyll a/b ratio was more sensitive to changes in lichen me tal content. A marked decrease in the ratio of chlorophyll a/b, from 3 .0 to 0.4 for C. convoluta and from 3.2 to 0.8 for C. rangiformis, occ urred when the thallus Cu content exceeded 175 and 200 mu g g(-1) DW, respectively. Zn and Pb caused a 10-15% decrease of the ratio of chlor ophyll a/b for C. convoluta at concentrations exceeding 140 and 20 mu g g(-1) DW, respectively. The chlorophyll a/b ratio of C. rangiformis was unaffected by increasing thallus Zn content, whereas an increase i n thallus Pb content caused a slight increase in the chlorophyll a/b r atio. The decrease in the ratio of chlorophyll a/b with increasing lic hen Cu content was caused by a decrease in chlorophyll a and an increa se in chlorophyll b concentration in both lichens. The Cu effects on c hlorophyll were reduced in the presence of Pb and Zn in both lichens, but to a lesser extent in C. rangiformis. Metal cations appeared to be ionically bound within the cell wall in an exchangeable form with bin ding affinities of Pb > Cu > Zn. It would appear that of these cations only Cu is taken up into the photobiont cells. Cu may interfere with the biosynthesis of chlorophyll or cause lipid peroxidation processes in the photosynthetic membranes. (C) 1998 Elsevier Science B.V. All ri ghts reserved.