Thomas H. Nash

Lichens as indicators of air pollution

Lichens are well known as sensitive indicators of air pollution, particularly for sulfur dioxide. In part, this is related to their unique biology. Evidence supporting this assertion goes back well over 100 years and is based on extensive field and laboratory studies. In general, these studies reinforce each other, but for oxidants the data are not entirely consistent, and consequently require further work. At the least, lichens appear to be less sensitive to oxidants than vascular plants. Acid precipitation effects are closely related to SO2 effects. The mechanistic basis for SO2 effects is briefly reviewed. The extreme sensitivity of lichens to SO2 is partially related to their ability to absorb more SO2 for a given concentration than typical vascular plants. The use of lichens as long-term integrators of elemental deposition patterns is well established, but their use for monitoring dry deposition has only recently been recognized. Air pollutants adversely impact not only growth, reproductive potential, and morphology, but also a wide variety of physiological processes, which also becomes reflected in ultrastructural changes. The impact of organic pollutants on lichens is largely undocumented and is a prime area for future work, even though much work remains to be accomplished with the traditionally recognized air pollutants.

Desiccation-Tolerance in Lichens: A Review

Abstract Desiccation-tolerance, the ability to revive from the air-dried state, is found in prokaryotes, algae and bryophytes, and occasionally in pteridophytes, but is very rare in the vegetative tissues of angiosperms or in animal tissues. However, the vast majority of lichens are desiccation-tolerant. Under natural conditions, the life of most lichens is characterized by rapidly changing water contents, and correspondingly rapidly changing physiological activity such as respiration and photosynthesis. Taken to the extreme, some lichens can revive after being desiccated under controlled laboratory conditions for many months. As a result of their desiccation-tolerance, lichens are extremophiles and can live in places no higher plant can. They may be the predominant life-form in ecosystems characterized by severe environmental stresses such as Arctic, Antarctic and alpine regions, as well as deserts. This review critically assesses our current knowledge about desiccation-tolerance in lichens, concentrating on mechanisms that protect from desiccation-induced damage. Evidence available from other desiccation-tolerant life-forms suggests that desiccation-tolerance is a multifaceted trait involving a suite of interacting mechanisms. The majority of recent studies on mechanisms of lichen desiccation-tolerance have focused on the scavenging of reactive oxygen species, which therefore forms a major part of this review. It is argued that effective control of reactive oxygen species and mutual up-regulation of protective mechanisms was critically important for the evolution of lichens, facilitating the transition from free-living fungi and green algae or cyanobacteria to the lichenized state. Recently developed tools of molecular biology, particularly from the -omics disciplines, have only just started to be applied to lichens. There remain many unsolved questions as to how lichens survive desiccation and the authors hope to encourage more scientists to investigate this intriguing phenomenon.

Lichens, bryophytes, and air quality

Bryologists and lichenologists are well aware of the differential sensitivity of bryophytes and lichens to air pollutants. However, governmental agencies and other scientists have not used the wealth of information to the fullest extent. It is hoped that this volume will help bridge the gap between the professional bryologist and lichenologist on the one hand and those who are concerned with assessing biological aspects of air FR EN DE

Mineral Cycling and Epiphytic Lichens: Implications at the Ecosystem Level

The nutrient contribution of lichens as litterfall in forests is discussed for a number of different ecosystems and it is hypothesized that lichens are important in capturing nutrients from wet deposition, occult precipitation, sedimentation, impaction and gaseous uptake. Most nutrients captured by these processes represent new nutrient inputs that would otherwise not be intercepted by the ecosystem. Part of these nutrients will be incorporated into lichen biomass and only become available upon death and decomposition, but a portion will be leached by precipitation and become deposited on the soil surface. Although quantifying nutrient sources, fluxes and pool sizes is a potentially complex task, we describe a simplified approach for determining whether lichens significantly affect the mineral cycling of a forest. Preliminary results for an oak woodland in California document that epiphytic lichens may reduce throughfall and alter throughfall chemistry.

Lichen communities on conifers in southern California mountains: an ecological survey relative to oxidant air pollution

In comparison with collections from the early 1900s when oxidant air pollution was essentially absent, 50% fewer lichen species were found on conifers during 3 yr (1976-1979) of collecting and sampling in the mountains of Southern California. Among the five mountain ranges studied, the San Bernardino Mountains, the region with the highest oxidant levels, had lower lichen frequency and cover values. Within the San Bernardino study sites, lichen cover was inversely related to estimated oxidant doses. Furthermore, at sites with high oxidant levels, marked morphological deterioration of the common species Hypogymnia enteromorpha was documented. Transplants of this species from the relatively unpolluted Cuyamaca Rancho State Park into the San Bernardino Mountains exhibited similar deterioration after a years exposure. 4 figures, 9 tables.

Influence of Effluents from a Zinc Factory on Lichens

Lichen species richness and abundance are reduced by approximately 90% in lichen communities near a zinc smelter at Lehigh Water Gap in comparison with the lichen communities of Delaware Water Gap. The principal cause of the impoverished lichen flora in the Lehigh Water Gap area is prob- ably high concentrations of zinc. Of the non-pollution and pollution factors considered, only abnormal soil concentrations of zinc and cadmium extend beyond the limits of the lichen impoverishment zone. Because Zn is present in concentrations generally 100 times higher than that of Cd and because Cd is experimentally shown to be no more toxic to lichens than is Zn, it is probable that Zn is the more important, detrimental factor to lichens in the Palmerton area. Near the smelters, Zn, Cd and sulfur dioxide are all present in sufficiently high concentra- tions to be detrimental to lichen growth and survival. However, at the perimeter of the lichen- impoverished zone, only Zn is present in high enough concentrations to be phytotoxic. Although microclimatic alteration in forested areas near Palmerton may be sufficiently great to be a stress for a few lichen species that are adapted to shaded conditions, no microclimatic differences were demonstrable between Delaware and Lehigh Water Gaps for open habitats where most lichen species normally occur in this area. Variations in such factors as lichen geographical range, climate, substrate composition and abundance, and fire history are probably of negligible importance in explaining the reduction in lichen numbers or abundance in Lehigh Water Gap.

Seasonal variation of elemental status in the lichen Ramalina menziesii Tayl. from two sites in southern California : evidence for dry deposition accumulation

Abstract In southern California the lichen Ramalina menziesii was transplanted from a relatively unpolluted area to a highly polluted area for three periods over a year. During each period multi-element analyses of both water leachable extracts and residual fractions from the leached thallus were analyzed at 2-week intervals. Total concentrations were calculated by adding these two measurements. Total concentration of most elements did not exhibit distinct seasonal patterns but the higher concentrations exceeded background levels by factors of 1.3–3.7, depending on the element. In contrast, the elements in the leachates at the control and the polluted site exhibited distinct seasonal patterns with higher concentrations generally present in summer than in winter. High leachable concentrations were only found during dry periods, and consequently the leachable fraction was assumed to represent primarily dry deposition accumulation, particularly as the magnitude of the differences was higher at the polluted site. These elemental patterns reflected not only atmospheric deposition patterns, but also intracellular release of elements as injury occurred and to a lesser extent accumulation of marine aerosols and soil particulates.

Historical and current atmospheric deposition to the epilithic lichen Xanthoparmelia in Maricopa County, Arizona

Spatial patterns of atmospheric deposition of trace elements to an epilithic lichen were assessed using a spatial grid of 28 field sites in 1998 throughout Maricopa County, Arizona, USA. In addition, samples of Xanthoparmelia spp. from Arizona State University lichen herbarium material (1975-1976) was utilized for a limited number of sites in order to explore temporal trends. The lichen material was cleaned, wet digested and analyzed by ICP-MS for a suite of elemental concentrations [antimony (Sb), cadmium (Cd), cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), dysprosium (Dy), europium (Eu), gadolinium (Gd), gold (Au), holmium (Ho), lead (Pb), lutetium (Lu), neodymium (Nd), nickel (Ni), palladium (Pd), platinum (Pt), praseodymium (Pr), samarium (Sm), scandium (Sc), silver (Ag), terbium (Tb), thulium (Tm), tin (Sn), uranium (U), ytterbium (Yb), yttrium (Y), and zinc (Zn)]. Cluster analysis and principal component analysis suggest three major factors, which, depending on regional aerosol fractionation, explain most of the variation in elemental signatures: (1) a group of widely distributed rare earth elements (2) a highly homogenous Co, Cr, Ni, and Sc component representing the influence of mafic rocks, and (3) anthropogenic emissions. Elemental concentrations in Maricopa County lichens were generally comparable to those reported for relatively unpolluted areas. Only highly urbanized regions, such as the greater Phoenix Metropolitan Area and the NW corner of the county, exhibited elevated concentrations for Zn, Cu, Pb, and Cd. Lead levels in lichens have fallen over the last 30 years by 71%, while Zn concentrations for some regions have increased by as much as 245%. From the spatial pattern of elemental deposition for Cd, Cu, Ni, Pr, Pb, and Cu, we infer that agriculture, mining, industrial activities, and traffic probably are the major air pollutant sources in Maricopa County.

On the relationship between nutrient use efficiency and fertility in forest ecosystems

The concept of nutrient use efficiency is central in understanding ecosystem functioning because it is the step in which plants can influence the return of the nutrients to the soil pool and the quality of the litter. There are several ways to define nutrient use efficiency, but a common way within ecosystem ecology is as the ratio of litterfall production per unit nutrient to the litterfall nutrient content. However, this ratio is not a valid measurement to examine nutrient use efficiency in relationship to ecosystem fertility because there is a strong autocorrelation between litterfall dry mass per unit of nutrient and the amount of nutrients. More appropriate statistical analysis of the relationship between the fertility of ecosystems and the amount of nutrients in the litterfall are inconclusive, but indicate that, at least in some cases, there is (1) no pattern, (2) higher nutrient use efficiency at intermediate-fertility sites or (3) higher efficiency at higher-fertility sites. There is, however, no indication that nutrient use efficiency is greater in nutrient-poor ecosystems. This conclusion has important consequences for ecosystem nutrient cycling. Given the lack of a clear, consistent relationship between site fertility and litterfall nutrients, there is little likelihood that such a feedback mechanism plays an important role in ecosystem nutrient cycling.

Physiological responses of the lichen Ramalina menziesii Tayl. To the Los Angeles urban environment

Abstract In southern California the lichen Ramalina menziesii was transplanted from a control area to a polluted area for three periods during a year. Net photosynthetic rates, recorded under standard conditions in the laboratory, chlorophyll contents and per cent phaeophytins were measured at 2-week intervals for samples from both sites. Druing summer periods at the polluted site chlorophylls and net photosynthesis declined substantially and per cent phaeophytins increased, but during the winter period no changes in these parameters wereobserved. At the control site little or no change in these parameters was observed during the transplant periods. During the winter there was no difference in net photosynthesis for samples collected from the two sites. During the summers the decline in the lichen at the polluted site was associated with the accumulation of 23 ions. Although not demonstrably toxic, nitrate concentrations alone explained over 75% of the variation of each physiological parameter. Fluoride was the second most important variable and it was probably accumulated to toxic levels.