CARDON, ZOE G*, LOUISE A LEWIS, and DEBORAH TYSER. Dept. of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT 06269. - Evolutionary physiology of photosynthesis in desert-dwelling green algae.
Green algal species live as components of microbiotic crusts in many
deserts of the world, enduring extremes of temperature, water
availability, and, perhaps, light. Using a phylogenetic approach, we
are investigating components of the photosynthetic physiology of
Southwestern US desert green algae and aquatic sister species from
three classes of green algae: the Chlorophyceae, Trebouxiophyceae, and
Charophyceae. Because these desert algae are similar morphologically,
sequence data from the 18S ribosomal RNA gene is required for
identification of related pairs of aquatic and desert species. We
hypothesize that the desert-living habit, which has evolved at least
six times in the green algae, is associated with enhanced
photoprotective mechanisms compared to photosynthetic physiology found
in the aquatic habit. To date, analysis of chlorophyll fluorescence
quenching in desert and aquatic sister species reveals that at least
within the Chlorophyceae and Trebouxiophyceae, desert algae exhibit
altered patterns of non-photochemical quenching (qNP) in response to
light relative to their aquatic relatives. Such changes in qNP are
indicative of altered energy dissipation mechanisms associated with
the photosynthetic apparatus, and may prove to be a physiological
feature common to desert algal lineages.
Key words: chlorophyll fluorescence, crust, desert, green algae, photosynthesis, phylogeny