Boreskov

OP‐27LICHENS COULD BE RESPONSIBLE FOR THE DEVELOPMENTOF FIRST ORGANIC‐MINERAL SOILSZavarzina A.* , ***, Zavarzin G.** , *** *Faculty of Soil Science, Moscow State University (Moscow), Russia**Winogradsky Institute of Microbiology of Russian Academy of Sciences (Moscow), Russia***Borissiak Paleontological Institute of Russian Academy of Sciences (Moscow), RussiaSoil formation is a major process in transformation of land surface into habitablebiosphere. Soil is differentiated from the weathering profile by presence of organic matterwhich mostly occurs as coatings on mineral grains. When in the history hypergenicweathering was complemented by accumulation of soil organic matter representsgeochemical problem of the large scale. Ultimate precondition for soil formation isdevelopment of terrestrial biota which serves as a source of precursor material for soilhumus. About 90% of humus is composed of humic substances (HS) ‐ recalcitrant andmacromolecular N‐containing products of dead organic matter hydrolysis and oxidativetransformation (humification). In modern soils the main structural precursors of HS arevarious polyphenols of plant origin. These undergo oxidative coupling with nitrogenous andother compounds to form polymeric substances. Fungal oxidases (laccases, peroxidases) areconsidered to be the major catalysts of the process. Thus, formation of soil organic profiles,analogues to those occurring in modern biosphere, requires presence of biota which servesas a source of phenolic compounds. The earliest steps in colonization of terrestrialenvironment might be linked to the microbial and algal biofilms on the weathered crust. Thisevent occurs in Early Proterozoic (Retallack 2003). However, bacteria and algae lack phenoliccompounds in sufficient amounts. The upper known limit for soil formation is Devonian(about 0.4 Ga) when colonization of land by vascular plants took place. Before this time nofossilized record of organic soils was found and it is not known when and how first organicsoils were formed.In the present work we are going to consider lichens as possible candidates responsiblefor early humification processes. Lichens are symbiotic organisms, comprising of a fungus(commonly Ascomycete) and the photobiont ‐ an alga (usually Trebouxia) and/or acyanobacterium (commonly Nostoc). In modern Earth they form the dominant plant cover inextreme environments. A variety of physiological and chemical adaptations enable75