Cell Structure and Physiology of Alpine Snow and Ice Algae
Due to climatic and orographic reasons, the occurrence of vascular plants in high alpine regions is limited. At locations that are not suitable for the establishment of higher plants because of exposure, substrate or other abiotic factors, cryptogams can
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Daniel Remias
13.1
“Lower Plants” in High Alpine Regions
Due to climatic and orographic reasons, the occurrence of vascular plants in high alpine regions is limited. At locations that are not suitable for the establishment of higher plants because of exposure, substrate or other abiotic factors, cryptogams can be the dominant life forms. Mosses, lichens and algae particularly thrive on places such as bare rocks, permafrost soils or, exceptionally, even in melting snow and permanent ice. Since these lower plants are poikilohydric and lack complex morphological tissues like the cormophytes, unfavourable conditions (like drought) can be overcome by physiological inactivity, and structural damage is not the critical issue for these poikilohydric organisms. The vegetation period of cryptogams can be very short (from days to a few weeks per year), and growth and reproduction have to be adapted to limiting factors such as low temperatures, limited water-availability or irradiation stress. While mosses and lichens are prominent representatives in places with sparse or almost no other vegetation, the virtual dominance of microalgae is somehow “cryptic” to the human eye, not only because of their size but also because of inconspicuous macroscopic signs of their occurrence in many cases. Alpine algae are neither limited to more familiar habitats such as permanent water bodies (lakes or streams), nor to
D. Remias (*) Institute of Pharmacy/Pharmacognosy, University of Innsbruck, Innsbruck, Austria e-mail: [email protected]
lichens as embedded phycobiont. In fact, many species are specialists in growing on bare surfaces such as stones (epilithic), in microcavities within rocks (endochasmolithic), at lower mountain ranges on tree bark (aerophytic), superficially in open habitats (e.g. soil crusts), subterrestrially in the first centimetres of the ground layer (soil algae) or – as is the main subject of this chapter – in wet snow and ice. All these niches are also frequently populated by cyanobacteria, which are typical primary successors in still ungrown places. However, in melting snow of the European Alps, these photoautotrophic procaryota have so far not been reported to generate populations. Generally, both cyanobacteria and green algae produce the first organic matter and form primary soils with nutrients that are available for mosses, higher plants or fungi after decomposition (Elster and Benson 2004). Although non-vascular alpine plants are less well investigated concerning their taxonomy and ecophysiology compared to vascular plants, it is assumed that they have also evolved a distinct speciation including ecophysiological strategies, which are necessary for survival in alpine (and in many cases similar polar) regions due to the adaptation to high altitude (or high latitude) ecosystems.
13.2
Snow and Ice as a Habitat
The “Red Snow” phenomenon is the probably bestknown case where macroscopic visible mass accumulations of microalgae attract the viewers’ attention. A historical background about discoveries
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