Natural and Experimentally-induced Zinc and Copper Resistance in the Lichen Genus Peltigera

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Abstract
Using a tolerance index based on metal-induced reductions in photosynthesis, members of the lichen genus Peltigera, sampled from a range of sites with contrasting metal status, were demonstrated to possess Zn tolerance directly proportional to the Zn content of the thallus. Tolerance was not related to the concentration of other cations present in the thallus or weight of thallus per unit surface area. Although differences in Cu tolerance were found, these were not related to the Cu content of the thallus but rather to the Zn content. In the laboratory, pretreatment of P. membranacea with low concentrations of Zn significantly decreased the inhibition of photosynthesis caused when subsequently supplied with high levels of Zn compared to water pretreated plants. Increased resistance to Cd but not Cu was also found, although it was not possible to increase either Cu or Zn resistance by pretreatment with Cu.