LEWIS, LOUISE A. Department of Ecology & Evolutionary Biology, University of Connecticut, Storrs, CT 06269-3043. - Green algae of desert microbiotic crusts: Survey of North American taxa.
Green algae are present in desert soils as components of microbiotic
or cryptobiotic crust communities, along with lichens, cyanobacteria
and other prokaryotes, non-lichenized fungi, and diatoms. Microbiotic
crusts can be found in arid and semi-arid regions world-wide, on a
large number of different soil types. Microbiotic crusts are
ecologically important, playing a role in nutrient cycling and soil
stabilization. There has been great interest in understanding the
ecological function of and taxonomic composition of crust communities.
The green algae that occur in crusts represent a diverse assemblage of
taxa spanning three classes of algae, the Chlorophyceae,
Trebouxiophyceae, and Charophyceae. They are genetically diverse, but
are morphologically simple unicells or packets of cells. In an ongoing
study of the diversity of microbiotic green algae from thirty
localities in western North America, a large number of green algal
taxa have been found, many of which represent new species and new
genera. Some genera, such as Bracteacoccus, are heavily
represented. Phylogenetic analyses using ribosomal RNA gene sequence
data have been a powerful tool in understanding the diversity and
evolution of desert crust green algae. These studies indicate that
microbiotic crust green algae evolved from aquatic green algae at
least five independent times. In addition, desert green algae are
always found to be derived from freshwater, not marine green algae.
Some lineages of green algae have a high proportion of desert taxa,
while other lineages of green algae have no known desert
representatives. Ongoing studies are addressing the ways in which
desert green algae are adapted to living in these conditions,
including adaptations to high light levels.
Key words: Chlorophyta, desert, diversity, microbiotic crusts, ribosomal rDNA