Nueve páginas y 6 figurasMicrobial ecology deals with interactions among microorganisms, between microorganisms
and their environment, and with water relations in the microhabitat. In the desiccated
state, many lichens tolérate long periods of intense stress. The present report describes
the use of scanning electrón microscopy with backscattered electrón imaging (SEM-BSE) to
observe - on the spatial nanometer scale - relationships among the epilithic thallus of an
Antarctic Lichen, microorganisms belonging to epilithic, chasmoendolithic and cryptoendolithic
communities and minerals. The main aim of the study was to determine the precise
location of minute quantities of water that the thallus may maintain probably obtained from
the mineral microenvironment of its rock habitat. Through low temperature scanning electrón
microscopy (LTSEM), it was possible to observe ice crystals indicative of the presence of
water in the dehydrated hyphae of the fungal partner of the lichen when these were crossfractured.
Ice crystals were also detected among the mineral particles of the lithic substrate.
Besides implications ¡n the highly controversia! topic of water distribution in the lichen thallus,
the present findings suggest that under conditions of drought, the presence of small quantities
of water in the apoplast may explain the survival of the dehydrated thallus.Grants BOS2000-1121 and ANT99-0680-CO2-02 from the DGICYT. The authors gratefully aknowledge Ana Burton for the English revision and Fernando Pinto for skilful technical assistence.Peer reviewe
