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The new genus Silobia M. Westb. & Wedin is proposed for the Acarospora smaragdula group, which is taxonomically and nomenclaturally revised in Sweden. The proposed taxonomy results from our former molecular phylogeny, together with morphological and anatomical investigations and analysis of secondary metabolites. Seven species are recognized in Sweden in this paper: Silobia dilatata sp. nov., S. myochroa sp. nov., S. rhagadiza comb. nov., S. rufescens comb. nov., S. scabrida comb. nov., S. smaragdula comb. nov. and S. tangerina sp. nov. Acarospora alberti, A. amphibola, A. isortoquensis, A. murina and A. undata are recognized as synonyms of S. smaragdula, Acarospora verruciformis as a synonym of S. scabrida and A. scyphulifera as a synonym of S. rhagadiza. The following names are lectotypified: Acarospora amphibola, A. amphibola f. testacea, A. lesdainii, A. lesdainii var. subochracea, A. murina, A. scyphulifera f. subdiscreta, Endocarpon smaragdulum, Lecanora rhagadiza and Sagedia rufescens. Acarospora scyphulifera is neotypified. Acarospora fusca is excluded from the Swedish checklist as the specimen was found to belong to S. rufescens. A key to the species is presented.
This volume focuses primarily on the influence of free-living fungi in biogeochemistry. Lichens, fungi that exist in facultative or obligate symbiosis with one or more photosynthesizing partners, also play an important role in many biogeochemical processes. Pioneer colonizers of fresh rock outcrops, lichens were possibly one of the first life forms to occupy Earth's land surfaces. The unique lichen symbiosis formed between the fungal partner (mycobiont) and the photosynthesizing partner, an alga or cyanobacterium (photobiont), enables lichens to grow in all surface terrestrial environments. These include extreme environments where no other multicellular vegetation can survive, such as the dry Antarctic valleys (Nash, 1996). An estimated 6% of the Earth's land surface is covered by lichen-dominated vegetation.
Globally, lichens play an important biogeochemical role in the retention and distribution of nutrient (e.g. C, N) and trace elements (e.g. Knops et al., 1991; Garty et al., 1995), in soil formation processes (Ascaso et al., 1976; Jones, 1988) and in rock weathering (Hallbauer & Jahns, 1977; Wilson et al., 1981; Wessels & Schoeman, 1988; McCarroll & Viles, 1995; Barker et al., 1997; Lee & Parsons, 1999). Lichens tend to accumulate trace elements such as lead, copper and other heavy metals of environmental concern (see below), including radionuclides (Yliruokanen, 1975; Nieboer & Richardson, 1981; Beckett et al., 1982; Boileau et al., 1982, 1985a, b; Richardson et al., 1985; Fahselt et al., 1995; Haas et al., 1998; McLean et al., 1998; Jacquiot & Daillant, 1999; Purvis et al., 2004).
Cellular responses to copper stress were investigated for the first time in a saxicolous lichen species, Lecanora polytropa (Hoffm.) Rabenh. Bright blue-green apothecia accumulated up to 1·3% Cu on a dry weight basis (205 μ mol Cu g−1), c. 50% in an exchangeable form. A bright turquoise-blue layer extended beneath the hymenium into the medulla, above and between a dentate photobiont layer. Oxalic (1·88 μ mol g−1), citric (0·83 μ mol g−1) and lower concentrations of malic (0·45 μ mol g−1) acids were determined by GC/MS analysis. Short-term exposure to high Cu2+ concentrations (40 and 400 μ mol g−1) under non-complexing conditions caused a dose-dependent decrease in chlorophyll a content; chlorophyll b and total carotenoid contents remained constant. The phaeophytinization quotient remained unchanged during Cu2+ exposure. Analysis of thiol peptides confirmed glutathione was reduced (GSH) in native L. polytropa (0·538 μ mol g−1), and phytochelatins (PC2 and PC3) oxidised. Short-term exposure to 40 μ mol g−1 Cu2+ oxidised c. 28% of the glutathione pool; oxidised phytochelatin concentrations remained unchanged. This is the first report of phytochelatin production and thiol peptide status in a crustose lichen. These represent two possible detoxification mechanisms in this Cu-tolerant species. Copper complexation by low molecular mass organic acids and non-protein thiols do not entirely account for its tolerance.
Oliver Gilbert was a pioneer, an outstanding field botanist and inspirational scientist. He worked in the broad fields of urban and lichen ecology and had almost 40 years of teaching and research experience within universities. Above all he was very approachable, an excellent teacher and fun to be with. Oliver was a leading figure in the British Lichen Society serving as BLS Bulletin Editor (1980–89 except 1987), President (1976–77) and was a frequent Council Member. He was elected an Honorary Member in 1997 and received the prestigious Ursula Duncan Award in January 2004. Oliver had an exceptional ability to find rare and interesting lichens and plant communities that others had overlooked and he constantly challenged conventional wisdom that particular habitats were uninteresting, especially urban habitats. His ecological ‘field craft’ skills were equally legendary. Passion for field work and British Lichen Society field meetings led him to organize a small grant awards scheme to stimulate others to attend field meetings and to submit their results for publication in the BLS Bulletin.
Biogeochemical signatures were compared in ‘living’ and ‘dead’ Parmelia sulcata samples with their oak bark substratum. Eighteen elements reached maximum concentrations in ‘dead’ lichens, at lower concentrations than reported from industrial regions. High N concentrations in ‘dead’ lichens confirm exceedances of critical levels established for deciduous woodlands, supported by alien algae and ‘nitrophytic’ lichen colonization. Negative δ15N values recorded in lichen samples indicate N originated mainly from ammonia. Less negative δ15N values in healthy samples near busy roads suggest local NOx accumulation by Parmelia. Higher δ15N values in bark may result from different processes. Twenty-eight elements reach higher concentrations in healthy lichens near roads carrying higher traffic volumes. Thirteen elements correlate positively with lichen δ15N, suggesting that δ15N is a powerful indicator of the balance between agricultural and vehicular N influx. Maximum Ca and Sr concentrations recorded in bark and their spatial distribution suggest a local geological origin. High concentrations of Ga, Ba, Pb and Ni bark contents testify to a previous pollution legacy, including that from petrol which carried higher lead concentrations than today. Mn concentrations are higher than reported from other studies and show no clear relationship with local roads. Mn is known to limit lichen diversity and health in coniferous forests in US and Germany, but not yet in deciduous woodlands. Current atmospheric conditions and the former pollution legacy must be understood to conserve epiphytes and for biomonitoring.
The lichen Trapelia involuta from uraniferous spoil heaps in Cornwall, England, growing directly on the secondary uranium minerals, metazeunerite and metatorbernite, was examined by field-emission scanning electron microscopy and transmission electron microscopy to assess the effect of Trapelia on uranium migration. We observed metazeunerite, sericite and scorodite as well as unidentified Fe-, Pb/As-, Fe/As-, Al/P-, Pb-bearing minerals concentrated in the lichen exciple and medulla. In addition, metazeunerite also occurred in the epithecium. The chemistries, sizes, and occurrences of the above minerals in the lichen suggest that fixation of U as well as Pb, As, Fe, and Al is dependent on lichen physiological processes. We suggest Trapelia accumulates these elements from groundwater and precipitates the above minerals within specific tissues. Our results indicate that some lichens retard uranium migration by accumulating uranium from groundwater and forming uranium-bearing minerals within their tissues.
The localization of psoromic acid and copper in partly green, copper-rich specimens of Lecidella bullata and Tephromela testaceoatra collected in Norway was studied by optical microscopy, scanning electron microscopy, and electron probe microanalysis. Infrared absorption spectroscopy of lichen material and of a synthetic copper-psoromic acid complex, and the other techniques, provide evidence that complexing of copper by psoromic acid occurs within specific areas of these lichens and this leads to their unusual colouration. In contrast, a specimen of copper-rich Lecanora cascadensis, which contains psoromic and usnic acids, does not contain such a complex. From the evidence obtained it is suggested that taxonomists should pay attention to the impact of rock and lichen chemistry on the appearance of lichen thalli.
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