title: Water relations and photosynthesis in the cryptoendolithic microbial habitat of hot and cold deserts.
abstract: Two cryptoendolithic microbial communities, lichens in the Ross Desert of Antarctica and cyanobacteria in the Negev Desert, inhabit porous sandstone rocks of similar physical structure.  Both rock types adsorb water vapor by physical mechanisms unrelated to biological processes.  Yet the two microbial communities respond differently to water stress:  cryptoendolithic lichens begin to photosynthesize at a matric water potential of -46.4 megaPascals (MPa) [70% relative humidity (RH) at 8 degrees C], resembling thallose desert lichens.  Cryptoendolithic cyanobacteria, like other prokaryotes, photosynthesize only at very high matric water potentials [> -6.9 MPa, 90% RH at 20 degrees C].
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee 32306-2043, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Palmer
authors.forename: E I
authors.initials: EI
authors.lastname: Friedmann
mesh_terms: D000864:Antarctic Regions; D002245:Carbon Dioxide / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism / Q000502:physiology*; D003889:Desert Climate; D017753:Ecosystem; D055593:Geological Phenomena; D005844:Geology; D006813:Humidity; D007557:Israel; D008011:Lichens / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology*; D013696:Temperature; D014867:Water
chemical_list: D014867:Water; D002245:Carbon Dioxide