METAL UPTAKE IN TERRICOLOUS LICHENS

S ummary Laboratory experiments critically assess the role of rhizinae and thallial surfaces of Peltigera canina in the accumulation and translocation of metals (Cu, Fe, Mn, Ni, Pb and Zn) from the external medium to and within the thallus. The patterns of metal localization, within the different thallial components (rhizinae, medulla and phycobiont) observed from the analyses of field materials, are supported by laboratory experiments. The rhizinae were found to be capable of absorbing, accumulating, translocating and regulating metals. Both upper and lower surfaces were capable of metal translocation. The mode of translocation through one or both of the two surfaces was very similar. Metal cations were able to move freely from the rhizinae to the upper thallial surface and vice versa. The rhizinae and medulla play a significant role in metal accumulation and translocation, especially at higher metal concentrations when the metal uptake capacity of the upper thallial surface is reduced. The observed competitive metal uptake sequences by the rhizinae and thalli with rhizinae removed were consistent with an ion‐exchange process modified by a metal complex formation. The loss of K induced by metals was maximal from the rhizinae and medulla. Most of the metal binding sites are interpreted as occurring near, on, or within the fungal hyphae. Finally, modes of tolerance to high metal accumulations and detoxification are discussed in the light of the following observations: metal localization within the thallus, the role of rhizinae and thallial surfaces in metal uptake, and the lichen's morphological and histological performances in metal‐polluted environments. The factors limiting metal uptake and the effect of metal accumulations on the lichen's biological performance are given.