Micromorphological and ultrastructural investigations of the lichen-soil interface

The lichen-soil interface for three terricolous lichens, Baeomyces rufus (H uds.) Rebend., B, roseus Pers. and Cladonia rangiferina (L.) Web., from dif ferent alpine sites was studied using micromorphological methods (thick and thin sections) and ultramicroscopy (ultra-thin sections). Contacts between lichens and their substrates are mainly via their fungal symbionts. For Ba eomyces, a close relationship between the lichen hyphae and soil minerals w ere revealed as well as associated physical processes (reorientation of min eral particles, biodegradation of the walls of plant debris, and granulo-fi brillar bonding between different elements). For Cladonia, the basal part o f the thallus degenerates; fungal hyphae escape from it and are incorporate d into the soil. The production of polysaccharide compounds by the hyphae s eemed to play an important role in the formation of organo-mineral aggregat es. Moreover, the lichen-soil relationships were complicated further by the activity of lichen-specific bacterial colonies. The results obtained at va rious observation scales showed that lichens were the principal agents of m ineral weathering and the incorporation of humic compounds into the mineral substrate, at least under those extreme climatic conditions where they are abundant. (C) 2001 Elsevier Science Ltd. All rights reserved.