Physiological attributes of the lichen Cladonia pleurota in heavy metal-rich and control sites near Sudbury (Ont., Canada)

Abstract

The recovery of lichen communities on metal-rich historical ore-roasting beds west of Sudbury has been slow, and our objective was to locate and measure metals in Cladonia pleurota, the most frequently encountered roast bed lichen species. Particulates incorporated into the thallus on or near the roast bed contained high Fe, Al, Cu and Ni, and inductively coupled plasma-atomic emission spectroscopy showed lower concentrations of heavy metals in the control site 60 km upwind than in the roast bed or an immediately adjacent forest. Wavelength-dispersive X-ray spectrometry indicated potentially toxic levels of Cu, Ni, Fe and Al in both the mycobiont and photobiont in the roast bed. The physiology of roast bed lichens was consistent with damage found in metal-treated photobionts in culture: lower concentrations of chlorophyll a, chlorophyll b and total carotenoids on or near the roast bed than in the control site. In addition chlorophyll a on the roast bed was more subject to phaeophytinization and the yield of photosystem II, as measured by F v/ F m, was significantly less in both of the metal-rich sites than in the control. Thin-layer densitometry and UV spectrophotometry showed no significant difference in the amount of usnic acid between metal-rich and control sites, but heavy metals were associated with crystals of usnic acid, possibly forming complexes.