| Lichens are symbiotic systems comprised of a fungus and an alga. Nuclear microscopy was used to study thin foliose lichen cross sections and lichen surfaces to determine element distributions. These distributions, along with scanning electron micrographs and other analyses, provide evidence for a unique function of calcium oxalate in the lichen family Parmeliaceae. Foliose lichens from the family Umbilicariaceae demonstrated no calcium oxalate accumulation. The lichen Dermatocarpon reticulatum also showed no calcium accumulation, but did demonstrate sulfur accumulation.; The results indicated that soluble elements of biological significance (i.e. phosphorus, sulfur, chlorine, and potassium) were often most concentrated around the algal layer. Transition metals also tended to be more concentrated around the algal layer. Elements associated with silicate minerals (silicon, titanium, iron, and manganese) were usually found in highest concentration in the lower and upper cortices.; Cross section data were inconclusive regarding pollution effects on lichen thalli, so scans of upper and lower cortices were done to determine the thallus element characteristics from an additional perspective. Element maps of Xanthoparmelia cumberlandia from Arizona show that particles are randomly distributed over the thallus. While still preliminary, this approach may further clarify the role of lichens as biomonitors of air pollution.; Accelerator mass spectrometry was used to measure 14C profiles in individuals of the crustose lichen Caloplaca trachyphylla at two sites. The profiles showed linear radial growth and an annual carbon turnover rate of 4.5%. Growth rates were constant for individuals at the same site, but differed by 80% between two sites. These data suggest that habitat has an important effect on growth. The implications of the data to lichenometry are also discussed. However, failure of the technique to measure growth rate in the crustose lichen Rhizocarpon geographicum represents a significant limitation. |
