Lichens as factors of pedogenesis in volcanic areas

The principal effects of lichen growth on mineral substrata are discussed with special reference to rock surface disintegration, mineral etching patterns and formation of oxalates, iron oxides and hydroxides, aluminosilicates and lichen acid-metal complexes. The release of organic molecules, such as oxalic acid and polyphenolic secondary products of lichen metabolism usually indicated as “lichen acids”, have been proven to play a key role in lichen weathering and neogenesis of poorly and well crystalline biominerals. Both physical and chemical properties of the rock substrate and morphology of the thallus may strongly differentiate extent and assemblage of the lichen-substrate contact zone. Nevertheless, differences in the bioweathering capability seems to be more related to the physiology of the lichen species involved. Recent and further progress in the study of the interactions between lichens and their rock substrata appears to be mainly relying on the utilisation of more specialised analytical and instrumental techniques and on the close collaboration among scientists from different research fields. The significance of the lichen bioweathering in the colonisation of rock outcrops by more exigent plant species and in the process of soil formation is remarked.