Recent records of environmental contamination noted a moderate decrease of SO2 pollution, whereas the burden of atmospheric heavy metals is still considerable. The present review refers to the entrapment, uptake, and accumulation of heavy metals by lichen thalli, made apparent by parameters of lichen vitality and stress. The particulate nature of airborne heavy metals is made evident by parameters referring to the entrapment of heavy-metal containing particles by lichen thalli. The mechanism of uptake of heavy metals, investigated by means of controlled experiments, refers to extracellular and intracellular uptake. The rate of absorption and the accumulation of heavy metals is dependent on morphological features of lichen thalli in addition to kind and intensity of emission sources and to nonanthropogenic factors such as climate and topography. The role of lichens as biomonitors is demonstrated by the case of lead. In contrast to data obtained by retrospective studies, using lichens as biomonitors of heav...

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Biomonitoring Atmospheric Heavy Metals with Lichens: Theory and Application

Comparison between the accumulation capacity of four lichen species transplanted to a urban site

Epiphytic macrolichens were sampled in 203, 0.38 ha plots in the Southeast United States. 176 lichen species were encountered. Gradient analysis revealed two major regional gradients in lichen communities. A multivariate model based on non-metric multidimensional scaling was used to assign gradient scores to plots, based on lichen species composition. The strongest gradient in the lichen communities corresponded to a macroclimatic gradient from the coast through the Piedmont to the Appalachian Mountains. The second major gradient was correlated with air quality, with pollution-tolerant species and lower species richness in urban and industrial areas, and pollution-sensitive species and high species richness in cleaner areas. Epiphytic macrolichens were sparse in urban areas with heavy industry. In many rural areas, lichens were luxuriant and diverse. Species richness was locally variable and only weakly related to the coastto-mountains gradient, with somewhat higher diversity in the mountains and lower diversity on the Piedmont and coast. The Forest Health Monitoring (FHM) program seeks to assess the condition and trend of the forests of the United States (NAPAP 1993; Riiters et al. 1992). FHM is linked with the national sampling grid established by the Environmental Monitoring and Assessment Program (EMAP) of the Environmental Protection Agency. Epiphytic lichen communities were included in FHM because they help to answer several key assessment questions. These questions concern the contamination of natural resources, biodiversity, forest health, and sustainability of timber production. Hundreds of papers worldwide (chronicled in the series "Literature on air pollution and lichens" in the Lichenologist) and dozens of review papers and books (e.g., de Wit 1983; Nash & Wirth 1988; Richardson 1992; Seaward 1993; Smith et al. 1993; van Dobben 1993) published during the last century, have documented the close relationship between lichen communities and air pollution, especially SO2 and acidifying or fertilizing nitrogen and sulfur-based pollutants. In a comparison of biological responses between nearby and remote areas surrounding a coal-fired power plant, lichens gave a much clearer response (in terms of diversity, total abundance, and community composition) than either foliar symptoms or tree growth (Muir & McCune 1988). Lichens were one of the few com0007-2745/97/145-158$1.55/0 This content downloaded from 157.55.39.187 on Wed, 30 Mar 2016 05:41:06 UTC All use subject to http://about.jstor.org/terms 146 THE BRYOLOGIST [VOL. 100 ponents of terrestrial ecosystems to show a clear relationship to gradients of acidic deposition in the eastern United States (NAPAP 1991; Showman 1992). Much of the sensitivity of epiphytic lichens to air quality apparently results from their lack of a cuticle and their reliance on atmospheric sources of nutrition. Although trees may respond to moderate, chronic levels of air pollution deposition, all of the other influences on tree growth, such as variation in soils, make the responses of trees to pollutants difficult to measure in the field. Lichen communities provide, therefore, not only a measure of air pollution impacts upon lichens, but also suggest air pollution impacts on aspects of forest health that are difficult to measure directly. Elemental content of lichens in the southeastern U.S. has received some study (e.g., Bosserman & Hagner 1981; Kinsman 1990; Walther et al. 1990), but no previous published studies of lichen community response to air pollution have been made in this area. Elsewhere in eastern North America, lichen community response to urban and industrial air pollution has been studied mainly in local urban and industrial areas (LeBlanc et al. 1972; McCune 1988; Muir & McCune 1988; Rao & LeBlanc 1967; Showman 1975, 1981; Will-Wolf 1980). Only Showman (1992) has studied lichen communities on a regional gradient in air quality in North America. In Europe, regional monitoring grids have focussed primarily on elemental analysis of tissues or status of particular species, with only a few largescale studies analyzing community composition (Bruteig 1993; de Wit 1976; van Dobben 1993). In addition to their utility as indicators of air quality, epiphytic lichens are an important component of many forests. Lichens often comprise a large portion of the diversity of macrophytic species in a forest. Lichens have numerous functional roles in temperate forests, including nutrient cycling (especially nitrogen fixation in moist forests; Pike 1978) and as components of food webs (Dawson et al. 1987; Maser et al. 1985; Maser et al. 1986; Rominger & Oldemeyer 1989; Servheen & Lyon 1989). The large-scale sampling of FHM using the EMAP sampling grid allows us to describe regional gradients in lichen community composition as influenced by climate and topography. A multidisciplinary regional sampling grid of this scale is unprecedented in North America, although transcontinental transects in Canada have addressed questions at a similar spatial scale (La Roi 1967; La Roi & Stringer 1976). The current data set extends from Georgia to Virginia, inland to eastern Tennessee. Additional data collected along the whole eastern seaboard in 1994 and 1995 will be analyzed in the future. CALIBRATION PHASE

Regional Gradients in Lichen Communities of the Southeast United States

Lichens are reviewed for their potential to reflect metal air pollution. They are discussed both as being symbiotic plants and as biomonitor organisms. The attention is focused on their biological performance, the dynamics of metal uptake and release, on particle interception and on (physiological) processes underlying metal accumulation within the thallus. Laboratory-linked detailed physiological assessments of lichen behaviour are recognized as are the more pragmatic approaches often adopted in field work. Lichen morphology and physiology are regarded as of similar relevance in overall metal accumulation. A simplified approach is discussed in which the lichen is seen as essentially “homogeneous”, in the sense that no symbiont-dependent differentiations are regarded, but where the lichen's morphological characteristics are seen as of importance in initial interception of airborne particles. Modelled results from this approach relative to field survey assessments indicate the potential of this view to a lichen. Discussed literature data on lichen physiology indicate that, in surveys, apart from lichen metal determinations, lichen behaviour may be critically viewed if not “normalized” by simultaneous analysis of selected lichen physiological parameters: apart from the assessment of the lichen's surface-to-mass ratio, a number of possible analyses are presented, among which the determination of leaching through damaged cell membranes, stress-ethylene, the rate of photosynthesis, the potential quantum yield of photosystem II, the lichen's spectral reflectance, or the lichen's chlorophyll content.

Chapter 11 Biomonitors in use: lichens and metal air pollution

The performance of two lichen species as bioaccumulators of trace metals.

Elemental compositions of two epiphytic Okefenokee Swamp lichens, Usnea and Parmelia, were examined. Differences between the two genera are ascribed to morphological and metabolic characteristics. These lichens occupy the same habitat in Okefenokee; therefore, elemental composition should reflect niche separation that allows the two genera to coexist. The fruticose lichen, Usnea, appears to depend more on atmospheric wetfall than dryfall, having higher concentrations of dominant precipitation elements (Na, Ca, Mg). The foliose lichen, Parmelia, appears to depend more on atmospheric dryfall than wetfall, having higher concentrations of dustfall elements (P, Si, Al, Fe, Zn, K). Substrate composition affects both lichens through either stemflow or direct substrate uptake. Elemental concentrations in Okefenokee lichens are similar to those of epiphytic lichens found elsewhere. Differences between genera are greater than differences between locations in Okefenokee. Lichen elemental content has become only recently a topic of interest in lichen research. The discovery that lichens concentrate pollutants has inspired researchers to look more closely at the role of lichens in ecosystem mineral cycling (Pike 1978; Lang et al. 1976; Touminen & Jaakkola 1973). Epiphytic lichens are inconspicuous components of most temperate forest ecosystems; however, in freshwater swamps, which can provide ideal habitats for epiphytic growth, lichens are often abundant and may play more important ecosystem roles. Much attention has been given to the abilities of lichens to absorb elements from their nutrient-poor environments; many lichens maintain greater concentrations of elements than do sympatric, terrestrial plants because of more efficient uptake mechanisms and longevity (Lounamaa 1965). Lichens are known to accumulate various trace elements and have been studied as effective pollution indicators and collectors of atmospheric radioisotopes (Jenkins & Davies 1966). Although lichen elemental composition has often been studied in terms of atmospheric pollution, little is known about the elemental content of epiphytic lichens in undisturbed ecosystems (Touminen & Jakkola 1973). This study examines distributions of 18 elements in two epiphytic lichen genera, Usnea and Parmelia, from Okefenokee Swamp. Differences in the morphological characteristics of the two genera, in substrate type, and in location within Okefenokee Swamp are hypothesized to account for much of the variation in elemental composition. Different species of epiphytic lichens often occupy the same habitat and partition their common nutrient environment by uptake characteristies, substrate preferences, and morphological adapta007-2745/81/48-58$1.35/0 This content downloaded from 157.55.39.249 on Wed, 03 Aug 2016 05:05:52 UTC All use subject to http://about.jstor.org/terms 1981] BOSSERMAN & HAGNER: ELEMENTAL COMPOSITION 49 tions. Among fruticose, crustose and foliose lichens, morphological differences that affect exposure to their environments should be reflected in elemental composition. In Okefenokee Swamp, Parmelia and Usnea coexist on dead and living branches of numerous Okefenokee trees and shrubs. Usnea is a fruticose or "beardlike" lichen with a stringy body that hangs from a single point of attachment. Usnea greatly depends on atmospheric factors because of its large surface area exposed to air. Atmospheric moisture dominates Usnea's ecology, hence the common name "fog lichen." Usnea is particularly sensitive to air pollution, making it an effective indicator of environmental conditions (Ferry et al. 1973). Although Usnea is attached to bark with fungal strands that penetrate cracks and lenticels, it apparently receives no nutrition through its basal holdfast (Brodo 1973). The most common Usnea species present in Okefenokee are U. florida (L.) Web., U. longissima (L.) Ach., and U. strigosa (Ach.) Eaton. Parmelia, on the other hand, is a foliose lichen, having a flat, leaflike thallus, which extends along branches and trunks of trees. Parmelia has more contact with its substrate than does Usnea, which has only a small basal holdfast. Usnea's thallus consists of numerous, long, thin cylinders, a form exposing to the atmosphere more surface area per unit biomass than does Parmelia's flattened thallus. Parmelia is attached to its substrate by numerous penetrating rhizines, but these apparently do not absorb nutrients from the substrate (Brodo 1973). Parmelia's gray thallus is comprised of numerous cup-like apothecia and depressions, suggesting an ability to accumulate atmospheric dryfall and wetfall. Rocks and trees in habitats are substrates for the cosmopolitan Parmelia. The most common Parmelia species in Okefenokee is P. perforata (Jacq.) Ach. METHODS AND SITE DESCRIPTION Okefenokee Swamp is a large wetlands area in southeastern Georgia and northern Florida, comprised of shrub swamp (34% of the total area), cypress forests (23%), aquatic macrophyte and grass sedge marshes (21%), and bay forests (6%) (Hamilton 1977). Study sites were chosen in aquatic-marsh shrub-swamp ecotone areas abutting Grand, Chase, Chesser, and Durdin Prairies and Billy's Lake. Lichens of the genera Parmelia and Usnea were collected from shrubs (angiosperms) and cypress (gymnosperms) from three randomly selected sites in these areas. Dominant shrubs included Cyrilla racemiflora, Ilex cassine, Lyonia lucida, Leucothoe racemosa, and Clethra alnifolia, with Cyrilla and Ilex being most abundant. Immature pond cypress (Taxodium distichum var. nutans) are intermixed with shrubs. In the laboratory, Usnea and Parmelia were separated from their respective cypress and shrub substrates; care was taken to remove as much bark as possible from lichens. Sorted lichens and their substrates were dried at 60'C in a forced air drying oven and ground with a Wiley mill. Half-gram samples were ashed at 500'C in a muffle furnace, dissolved in a 20% nitric acid solution, and analyzed with a Jarrell Ash plasma emission spectrograph for 18 elements: P, K, Ca, Mg, Fe, Mn, B, Cu, Zn, Na, Al, Si, Co, Cr, Ni, Pb, Cd and Sr. Orchard leaf standards from the National Bureau of Standards were used to calibrate the spectrograph. Interferences from the ionic matrix were examined by making standard additions of the measured elements to a single plant sample (Bosserman 1979). All elements in the sample were above the detection limit of the instrument. More information about detection limits, matrix interferences, machine variability, and percent recovery for this method and this particular instrument are being published elsewhere (Blood et al. 1980; Blood, pers. comm.). Combined wet and dry precipitation samples in various Okefenokee locations were collected in polyethylene containers over two week periods during the year preceding the sampling period. The precipitation samples were concentrated on a hotplate, placed in a 20% nitric acid solution, and analyzed for the above 18 elements on the plasma emission spectrograph. Water samples with known concentration were used to calibrate the instrument (Blood et al. 1980). Statistical analyses were done using SAS 76 (Barr et al. 1976). Analysis of variance and correlation analyses were done using GLM and CORR procedures, respectively. Duncan multiple range tests were used to describe significant differences among means (0.05 level). Genus, substrate type, and location were factors included in a statistical model, in which a percentage of element content variThis content downloaded from 157.55.39.249 on Wed, 03 Aug 2016 05:05:52 UTC All use subject to http://about.jstor.org/terms 50 THE BRYOLOGIST [Volume 84 TABLE 1. Elemental concentrations (ppm) of Usnea and Parmelia from Okefenokee Swamp. Values are means from all locations and substrates. * P(Ho:equal means) < 0.01, ** < 0.001, *** < 0.0001. Usnea (ppm) Parmelia (ppm) ? (SD) i (SD) Element n = 40 n = 43 Usnea concentrations greater than Parmelia Ca 3600 (1300) 2000 (1300) *** Mg 810 (170) 410 (210) *** Na 240 (50) 160 (60) Sr 15 (4.1) 10 (4.1) *** Parmelia concentrations greater than Usnea K 1500 (230) 2000 (470) *** Fe 290 (70) 370 (90) *** B 13 (6) 32 (33) ** Zn 23 (4) 31 (7) Al 440 (110) 760 (240) *** Si 310 (39) 360 (100) * P 190 (30) 320 (90) Usnea concentrations same as Parmelia Ash 19,000 (6000) 26,000 (2700) Mn 64 (22) 71 (59) Cu 4.7 (0.9) 5.6 (3.3) Co 0.3 (0.12) 0.2 (0.20) Cr 1.0 (0.3) 0.8 (0.4) Ni 1.2 (0.3) 1.3 (1.5) Pb 29 (7.0) 31 (10.3) Cd 0.3 (0.1) 0.3 (0.2) ability is attributed to each factor. From this model, the relative importance of elemental sources and the influences of generic differences, substrate type and location are established.

Elemental Composition of Epiphytic Lichens from Okefenokee Swamp

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Elemental Composition of Epiphytic Lichens from Okefenokee Swamp