Concentrations of Ten Elements in Two Common Foliose Lichens: Leachability, Seasonality, and the Influence of Rock and Tree Bark Substrates

Abstract

Concentrations often elements were studied in two morphologically similar species of foliose lichens (Flavoparmelia baltimorensis and F. caperata) that grow on tree bark and granite boulders in Rhode Island, to document the influence ofsubstrates on thallus element content. There were large differences in the concentrations of phosphorus, potassium, calcium, and zinc between F. baltimorensis thalli growing on granite boulders and thalli growing on adjacent Quercus bark. The large differences in calcium concentrations between epiphytic (0.08% Ca) and epilithic (0.73% Ca) F. baltimorensis thalli were due to substrate differences rather than atmosphere or precipitation differences. Concentrations of nitrogen, potassium, calcium, copper, iron, and zinc were higher in F. baltimorensis and F. caperata thalli growing on Q. borealis bark than in thalli growing on Q. alba bark. Comparisons between lichen thalli growing on different Quercus species corroborated the influence of substrate element content on thallus element concentrations for some elements, but not others. Zinc was the only element that was significantly higher in one Flavoparmelia species than the other when both grew on the same bark substrate. Leaching experiments indicated that the ten elements measured were not easily leachedfrom F. baltimorensis thalli and that these thalli did not contain high amounts of soluble surface deposits when collected. Phosphorus (250% higher in winter than summer) and sodium (27% higher in summer than winter) exhibited the highest temporal variations in F. baltimorensis thalli. There is presently no consensus regarding the relative contribution of atmosphere-, precipitationand substrate-derived elements to the nutrition of lichens. The relative importance of these three element pools appears to vary among sites, among lichen species, and among elements. Wet and dry deposition have both been reported as the primary source of elements for lichen growth (Brown 1976; Jenkins & Davies 1966; Manning & Feder 1980; Rasmussen et al. 1980), yet other studies have indicated that the substrate on which lichens grow is an important source of elements for some lichens (Bosserman & Hagner 1981; Brodo 1973; de Bruin & Hackenitz 1986; Dormaar 1968; Lounamaa 1965). The occurrence of two lichen species in Rhode Island that grew on different substrates at the same site provided the opportunity to investigate the relative contribution of atmospheric and substrate inputs to lichen element content (Prussia 1990). These two lichens, Flavoparmelia baltimorensis (Gyelnik & F6riss) Hale and F. caperata (L.) Hale, are pseudosibling species that are morphologically very similar, yet can generally be assigned to species by the accustomed eye (Culberson 1986). The appearance of both lichen species is so nearly identical that both were commonly recognized as F. caperata until the use of thin-layer chromatography demonstrated their biochemical differences (Hale 1976). Within its 'Current address: Goodwin Conservation Center, R.F.D. 1, Box 100, North Windham, CT 06256. 0007-2745/91/135-142$0.95/0 This content downloaded from 157.55.39.70 on Tue, 06 Sep 2016 05:48:07 UTC All use subject to http://about.jstor.org/terms 136 THE BRYOLOGIST [VOL. 94 range, F. caperata is the most frequently collected foliose lichen species (Hale 1976) and grows on Quercus alba L. and Q. borealis Michx. in Rhode Island. Its lower cortex is sparsely to moderately rhizinate and its hydrophobic, diffuse granular soredia erupt from the upper cortex. Flavoparmelia baltimorensis is equally abundant in Rhode Island, and although less common on trees than its congener, it readily colonizes the surfaces of granite boulders (Hale 1979). The lower cortex of this species is moderately rhizinate and its upper cortex is covered with coarse isidia that are hydrophilic. Preliminary analyses indicated that differences in element concentrations between F. baltimorensis and F. caperata growing on the same substrate were less than differences between thalli of the same species growing on different substrates. This observation of differences in element concentrations between sympatric lichens exposed to identical atmospheric conditions prompted further study of the relationship between the element content of these lichen species and their substrates. Although the primary focus of this study was the relationship between element concentrations in Flavoparmelia lichens and their substrates, additional questions regarding seasonality and leachability of elements in lichen thalli were examined. The following specific questions were addressed: 1) What are the concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, copper, iron, manganese, sodium, and zinc in the thalli of F. baltimorensis and F. caperata?; 2) are concentrations of elements in Flavoparmelia thalli influenced by the bark and granite substrates on which they grow?; 3) does leaching alter the element content of Flavoparmelia thalli?; 4) do element concentrations in Flavoparmelia thalli differ between summer and winter?