Photosynthetic organisms, i.e., plants, algae, cyanobacteria and photosynthetic bacteria, have developed efficient systems to harvest the light of the sun and to use the light energy to drive their metabolic reactions, such as the reduction of carbon dioxide to sugar. It is through photosynthesis that Earth's biosphere derives its energy from sunlight. On the other hands, cyanobacteria are the most ancient oxygen-releasing pho-tosynthetic organisms on the Earth. The stromatolite fossils and carbon isotope ratios confirm that autotrophs fixing carbon via the Calvin cycle must have existed for 3.5 billion years (Schopf and Packer 1987). The characteristic fossil structures formed by cyanobacteria were discovered on the Precambrian rocks and, probably, on meteorites (Zhmur et al. 1999; Boyd 2001). There is also an opinion that green algae were originated from symbiosis of cyanobacteria and a non-photosynthetic eukaryotic ancestor (Margulis 1993; Douglas 1998), the origin of photosynthetic eukaryotes that gave rise to the first alga having occurred 1.5 billion years (Yoon et al. 2004). Early algae probably gave rise to multicellular plants (Graham 1996).

Photoautotrophic microorganisms live mostly in aquatic environments, but some unicellular and filamentous algae and cyanobacteria dwell in moist soils; others join with fungi to form lichens. A number of microscopic algae and cyanobacteria inhabit different extreme environments, such as cold waters and ice, hot springs and geysers, acid ponds or salt waters, dry hot and cold deserts. A description of diverse communities of microalgae and cyanobacteria in cold habitats such as the Arctic and Antarctic lakes, rivers, seas, sea ice, glaciers, cold soils may be found elsewhere (Malone et al. 1973; Friedmann and Ocampo 1977; Sinclair and Ghiorse 1989; Getsen 1990; El-Sayed and Fryxell 1993; Nienow and Friedmann 1993; Palmisano and Garrison 1993; Vincent et al. 1993a, b; Abyzov et al. 1998; Priscu et al. 1998; Willerslev et al. 1999; Comte et al. 2007).

Tatiana A. Vishnivetskaya

Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences, 142290, Pushchino, Moscow Region, Russia; Current address: Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, Tennessee 37831, USA [email protected]

R. Margesin (ed.) Permafrost Soils, Soil Biology 16,

DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009

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