Locating water in the dehydrated thallus of lichens from extreme microhabitats (Antárctica)

Abstract

Microbial 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.