Water Storage in the Lichen Family Umbilicariaceae

Abstract

Quantitative relationships between thallus structure and water storage and retention capacities in 12 species of the lichen family Umbilicariaceae were explored using three recent techniques for plant structure analysis: stereology (3D quantification of microscopic images), mercury intrusion porosimetry (determination of pore size distribution of tissues) and lowtemperature scanning electron microscopy (LTSEM). Water storage capacity of the thallus was related neither to thallus density nor surface area of the thallus; it was directly related to the total porosity of the thallus and inversely related to the proportion of thallus volume occupied by cell walls and gelatinous substances. Water retention capacity increased with increasing thallus density and was decreased by slight increases in the surface area of the upper side of the thallus. Water storage and retention capacities exhibited a positive correlation only when the storage capacity was expressed on a surface area basis. LTSEM study of fully hydrated specimens revealed that many intercellular spaces of the upper cortex and upper parts of the algal layer contained liquid water. Intercellular spaces of the lower part of the algal layer and medulla were in general either airfilled or partially occupied by gelatinous substances. Species with rhizinomorphs and substrate-hygrophytic (water uptake from surface run-offs) stored more water and retained it longer than aerohygrophytic species (water uptake from the atmosphere) lacking rhlzlnornorphs. Thallus structure of aerohygrophytic species seems to facilitate rapid gas exchange with the environment, improving water uptake and carbon gain when atmospheric moisture is available but accelerating dehydration when the atmosphere becomes dry.

Diversity and ecological adaptations in Palaeogene lichens

“…For example, the narrow and abundantly branched lobes of fruticose lichens and the thin layers of air between the rhizoids of many foliose lichens facilitate evaporation and gas exchange, and thus contribute to the maintenance of positive primary production. In addition, the loosely interwoven medulla and cortical perforations facilitate gas exchange, allowing lichens to maintain relatively high water contents without experiencing a concurrent depression in photosynthesis [41][42][43] . As a whole, many structural features in the Palaeogene fossil lichens helped to combine sufficient intrathalline water storage and maximal gas exchange efficiency, which is especially important in moist and shady forest habitats where epiphytic lichens regularly experience prolonged periods of thallus hydration.…”

Shackletonia cryodesertorum (Teloschistaceae, Ascomycota), a new species from the McMurdo Dry Valleys (Antarctica) with notes on the biogeography of the genus Shackletonia

“…Parts of some S. cryodesertorum thalli sometimes develop microfruticose morphs, with rhizomorph-like structures on the bottom as well. This seems to be a common feature displayed by lichens growing on Antarctic rocks and could be related to higher water retention capacity and light harvesting efficiency (Sojo et al 1997;Valladares et al 1998). Shackletonia hertelii differs by its areolate thalli, the initial dark orange colour of the apothecial disc and the apically noninflated paraphyses (Søchting et al 2004).…”

A review and evaluation of forest canopy epiphyte roles in the partitioning and chemical alteration of precipitation

“…Measuring solely phytotelmata, however, neglects canopy water storage on outlying surfaces and may lead to underestimation. For lichens, sampling should attempt to capture the range of each species' thallus size and properties as these have been linked to large intraspecific variation in water storage and retention time (Valladares et al, 1998;Fos et al, 1999).…”