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Hair lichens are distinctive for their capillary growth and typically arboreal occurrence, especially in temperate and boreal forests. They consist of two morphogroups based on cortical pigments: a brown-black group with fungal melanin and a pale yellow-green group with usnic acid. Here we test the hypothesis that these morphogroups are ecologically distinct and thus appropriately regarded as functional groups. We examine their respective horizontal occurrence in the lower canopy of 60-year-old conifer forests on a 250 m tall volcanic cone in south-central British Columbia. Trees on open south-facing slopes and near the summit were found to support mainly melanic hair lichens (Bryoria and Nodobryoria), whereas more densely spaced trees on north-facing slopes and at the base had higher cover values of usnic lichens (especially Alectoria sarmentosa and Ramalina thrausta). The cover of melanic hair lichens was strongly correlated with canopy openness but not for their usnic counterparts. We suggest that investment in light-absorbing melanic pigments is an extreme form of specialization for high light, favouring persistence in dry, sun-exposed canopies of otherwise cool forests. By contrast, the cortex of pendent usnic hair lichens appears to facilitate optimum light transmission to underlying photobionts in shaded sites, though at the cost of sensitivity to light in open habitats, especially in rather dry regions.
Lichen extinction occurs at rapid rates as a result of human activity, although species could potentially be rescued by conservation management based on ecophysiological knowledge. The boreal old forest cyanolichen Erioderma pedicellatum currently occurs in few sites worldwide. To protect it from extinction, it is essential to learn more about it. The last remaining good European site is a canyon with a waterfall, in a low-rainfall region of Norway. Here, a spatially restricted population of 1500–2000 thalli dominates the epiphytic vegetation of a small number of Picea abies canopies. We were able to document that 1) E. pedicellatum grew on thin branches with higher bark pH than is normal for P. abies in a canyon that provided an unusual combination of very high light, high air humidity, and cool temperatures in the growing season. However, the species did not inhabit the main waterfall spray zone. 2) Erioderma pedicellatum had a high light saturation point, high CO2 uptake at high light (≥ 600 μmol m−2 s−1) and cool temperatures (5–20 °C), and experienced strong suprasaturation depression of photosynthesis when fully hydrated. 3) It showed good tolerance of desiccation and high light; it was slightly more tolerant than the morphologically similar, but more common cyanolichen Pectenia plumbea. 4) The European population in its sunny habitat had higher water holding capacity than previously recorded in slightly shaded rainforest populations in Newfoundland, consistent with acclimation to compensate for high evaporative demands. Understanding the ecological niche and responses to critical environmental factors is essential for action plans to avoid extinction of E. pedicellatum. Methods used in this study could also be applicable for ecological understanding of other threatened lichen species.
Some lichenized ascomycetes synthesize melanic pigments in their upper cortices when exposed to ultraviolet light and high solar radiation. Our previous work showed that melanized chloro- and cyanolichens from both high light and more shaded habitats were less photoinhibited than pale ones during controlled exposure to high light. However, protection from high light might not necessarily be the consequence of just sun-screening by melanins in upper cortices. An inherent problem with earlier experiments was that the photobionts of melanized thalli might have received more light than those beneath pale cortices. The photobionts may therefore have possessed other light-induced tolerance mechanisms that gave protection from photoinhibition. Here, we aimed to test directly the inherent tolerance of lichen photobionts to photoinhibition. The method involved removing the lower cortices and medullas of three lichen species, Cetraria islandica, Crocodia aurata and Lobaria pulmonaria, and exposing the photobionts to light from below. Results confirmed that most of the improvement in tolerance to photoinhibition in melanized lichens derives from fungal melanization in the upper cortex. However, in C. islandica, the most heavily melanized species, algae from melanized thalli possessed a significantly higher tolerance to photoinhibition than those from pale thalli, suggesting that photobionts can also adapt themselves to high light.
Hydration traits determine much of a lichen’s distribution pattern along a climatic gradient but the mechanisms involved are still incompletely known. A higher abundance of large external cephalodia in wet oceanic than in drier climates has previously been reported in Lobaria amplissima. This study aims to quantify how much more rain L. amplissima thalli with external cephalodia would need to fill their internal water holding capacity (WHCinternal) than thalli without. The mean WHCinternal was 1·8 times higher in thalli with external cephalodia than in those without. The WHCinternal when converted to mm rain needed to saturate an average specimen was 1·37 mm (min–max: 0·55–3·8 mm) for a cephalodiate thallus, whereas an average thallus without external cephalodia needed just 0·76 mm (min–max: 0·36–1·3 mm). Known dewfall rates and rates of water uptake from humid air are far below what is needed to saturate even the cephalodiate thallus with the lowest WHCinternal, implying a stronger dependency on rain for thalli with external cephalodia. Thus, the observed trends in this study are consistent with earlier reports of decreasing frequency of external cephalodia from wet to drier climates.
This study aims to quantify the size-dependency of important hydration traits in Lobaria amplissima, L. pulmonaria and L. virens sampled in sympatric populations on deciduous tree trunks in southern Norway, and to discuss possible implications of species-specific traits for the ecological niches of these old forest cephalolichens. Traits measured were thallus size (area and mass), specific thallus mass (STM), internal (WHCinternal) and external water-holding capacity (WHCexternal), and water content (WC) after shaking and after blotting. Lobaria amplissima had the highest WHCinternal, 2·6 times higher than L. pulmonaria with the lowest WHCinternal. WHCinternal, driven by STM, strongly depended on size. WHCexternal was 28% (L. virens) to 47% (L. pulmonaria) of the WHCinternal. Unlike WHCinternal, WHCexternal did not depend on thallus area, meaning that WHCexternal is proportionally higher for smaller compared with larger thalli. The most widespread species, L. pulmonaria, benefits from a flexible hydration strategy due to low STM, facilitating the use of more diverse water sources than the other two species that depend more on rain, particularly L. amplissima with the highest STM and thus relatively high WHCinternal. For L. virens, a combination of less specialized hydration traits and a low tolerance to higher light intensity probably jeopardizes its survival outside rainforest habitats.
Lichens as sessile and slow-growing symbiotic associations have evolved various carbon-based secondary compounds (CBSCs) to mitigate the effects of some stressors in the extreme environments in which they often grow. The mat-forming lichen Cladonia stellaris, an important fodder for reindeer, produces usnic acid in the outermost layer and perlatolic acid in the medulla. Here, we studied effects of simulated global warming on these CBSCs in C. stellaris cultivated in climate chambers with: 1) ambient conditions as control or 2) ambient conditions +4°C. The chambers simulated, at an hourly resolution, an averaged 10-year growing season dynamic from a long-term monitored boreal mire in northern Sweden. After two months of acclimation, +4°C warming in one simulated growing season increased the concentration of usnic acid by 31% compared with ambient conditions, whereas the warming decreased the concentration of perlatolic acid by 14%. Since lichen CBSCs play important roles in ecosystem processes such as lichenivory and decomposition, these changes may profoundly affect lichen-dominated ecosystems.
In order to improve growth chamber protocols for lichens, we tested the effect of 1) wet filter paper versus self-drained nets as a substratum for lichens, and 2) gradual versus abrupt transitions between dark and light periods. For Lobaria pulmonaria (L.) Hoffm. cultivated on nets, RGR increased by 60% compared to those on wet papers, whereas abrupt on/off transitions between day/night gave as high growth rates as gradual transitions mimicking sunrise/sunset. Because thalli on nets had less surface water than those on papers, the higher RGR on nets likely resulted from less suprasaturation depression of photosynthesis. By supporting very high growth and eliminating any visible damage, the revised growth chamber protocols facilitate new functional lichen studies.
Relative growth rates (RGR) and carbon-based secondary compounds (CBSCs) were quantified in four dominant terricolous arctic-alpine mat-forming lichens with different preferences for snow cover. The aim was to evaluate the effects of snow depth, and thus snow cover duration, on lichen growth and performance. The species, Alectoria ochroleuca, Flavocetraria nivalis, Cladonia mitis and Cetrariella delisei, are associated with increasing snow depth, respectively. They were transplanted for one year at five snow depths (0, 60, 120, 160 and 200 cm measured in early May) along each of four natural ridge to snow bed gradient transects in oceanic-alpine sites (western Norway). Snow slightly thicker than in source habitats caused negative RGR in the ridge top-dependent A. ochroleuca and the co-occurring F. nivalis with somewhat higher snow tolerance. Only C. mitis with the broadest ecological niche had positive RGR along most of the gradients (0–160 cm), even outside its natural range. The most snow-tolerant species, C. delisei, tolerant also to temporal inundation in water, had the lowest RGR. Nevertheless, it performed as well in places with little or no snow as in places where it grows naturally. Snow depth significantly affected total concentrations of CBSCs mainly in A. ochroleuca, which experienced substantial mass loss under snow. There was a highly significant increase in usnic acid concentration with increasing mass loss in A. ochroleuca, probably because usnic acid decays more slowly than other components. In conclusion, snow reduced lichen RGR, but in species-specific ways. Therefore, increasing snow depth per se along spatial and/or temporal scales likely reduces abundance and distribution of dominant mat-forming lichens in the alpine ecosystems of Scandinavia.
This study aims to quantify dispersal of airborne traffic-related elemental pollutants and concurring responses – relative growth rate (RGR), maximal quantum yield of PSII (Fv/Fm), and chlorophylls (Chl ab) – in four epiphytic lichens (Lobaria pulmonaria, Parmelia sulcata, Ramalina farinacea, Usnea dasopoga). Lichens were transplanted from 25 September to 26 March to 1·5 m tall stands in open farmlands at 10, 15, 30, 50 and 100 m from the E6 highway (SE Norway), along three transects on each side usnea dasopoga of the road. The concentrations of most elements (Ca, Mg, Na, Fe, Al, Zn, Ba, Cu, V, Cr, Ni, Co, Sn, As, Mo) significantly increased with increasing proximity to the road. Elements in bold had elevated concentrations relative to controls, at least in some species at 100 m. The heavy metal accumulation increased from foliose to fruticose lichens in the order: P. sulcata>L. pulmonaria>R. farinacea≫U. dasopoga. However, L. pulmonaria was the only species with strong pollutant-dependent reductions in growth, Fv/Fm, Chl ab, and Chl a/b-ratio. The RGR and viability parameters were adversely affected by the roadside environment near the road only (≤15 m), and only after substantial heavy metal accumulation. Measurement of metal accumulation in lichens is thus a far more sensitive way of monitoring road pollutants than recording growth and lichen viability. Despite strong species-specific contrasts in elemental concentrations, most road pollutant elements responded similarly to distance from the road in all species.
This review is a first attempt to combine and compare spatial distribution of the three main water sources, rain, dew and humid air, with water-related traits of mainly epiphytic macrolichens in a conceptual and functional model. By comparing climatic and lichenological knowledge, various effects of dewfall, rainfall and humid air on epiphytic lichen morphology and function are analyzed to search for traits and patterns. Although dew, rain and humid air cause lichen hydration and activate photosynthesis, these atmospheric hydration sources influence and shape lichens differently. In order to visualize hydration patterns, dew, rain and humid air are shown as corners in a triangle exhibiting the various combinations of these hydration sources. The sources of hydration vary on temporal scales, and on the spatial scales: regional, landscape, stand and tree. Lichen growth form, photobiont type, water-holding capacity (WHC) and suprasaturation depression show clear patterns within the hydration triangle. For most lichen species, one average pre-dawn dewfall approximately fills their average internal WHC. This suggests that lichens are optimally designed to utilize dew rather than rain, consistent with literature emphasizing dew as a driver for annual C-assimilation in chlorolichens. However, rain is needed to fill their external WHC and to fully hydrate most cyanolichens. Including the sources of hydration and internal lichen variables, such as water-holding capacity, will improve modelling of local and global future scenarios on lichen distribution and biomass production.
This study compares the success of vegetative diaspore establishment of the old forest lichens Lobaria pulmonaria and L. scrobiculata sown on Picea abies branches in boreal rainforests. The larger diaspores of L. pulmonaria (green algal photobiont) established more successfully, and showed a greater flexibility in ecological amplitude, than the smaller diaspores of L. scrobiculata (cyanobacterial photobiont). The establishment success apparently depended on species-specific differences in morphological and physiological traits of the diaspores. Both species established as well in young plantations as in old forests. Lobaria scrobiculata was most successful on short branches and small trees. In contrast, L. pulmonaria responded positively to trunk circumference in the old stands. The establishment success of both species decreases with increasing canopy openness, indicating that the soredia/isidioid soredia failed to establish on the most exposed branches. The probability of establishment did not change with bark-pH or with distance from the nearest stream. Despite a successful establishment in regeneration forests, the long-term survival in managed forests is still uncertain.
Gastropod abundance was quantified in forest litter around 33 trees harbouring Lobaria pulmonaria in southern Norway. In total, 1709 snails representing 28 species were found, and the number of snail species strongly increased with the total number of specimens found. Number of snail species, as well as snail abundance, was highest around trees on high pH soils. There was a positive relationship between number of snail specimens and cover of grazing traces on L. pulmonaria, presumably because calcareous soils facilitate both litter dwelling and climbing gastropods. The results suggest that gastropods may limit the distribution of L. pulmonaria in calcareous broad-leaved forests.
This study of elevation gradients of lichen species richness in Nepal aimed to compare distribution patterns of different life-forms, substratum affinities, photobiont types, and Nepalese endemism. Distribution patterns of lichens were compared with elevational patterns shown by a wide range of taxonomic groups of plants along the Nepalese Himalayan elevational gradient between 200–7400m. We used published data on the elevation records of 525 Nepalese lichen species to interpolate presence between the maximum and minimum recorded elevations, thereby giving estimates of lichen species richness at each 100-m elevational band. The observed patterns were compared with previously published patterns for other taxonomic groups. The total number of lichens as well as the number of endemic species (55 spp.) showed humped relationships with elevation. Their highest richness was observed between 3100–3400 and 4000–4100m, respectively. Almost 33% of the total lichens and 53% of the endemic species occurred above the treeline (>4300m). Non-endemic richness had the same response as the total richness. All growth forms showed a unimodal relationship of richness with elevation, with crustose lichens having a peak at higher elevations (4100–4200m) than fruticose and foliose lichens. Algal and cyanobacterial lichen richness, as well as corticolous lichen richness, all exhibited unimodal patterns, whereas saxicolous and terricolous lichen richness exhibited slightly bimodal relationships with elevation. The highest lichen richness at mid altitudes concurred with the highest diversity of ecological niches in terms of spatial heterogeneity in rainfall, temperature, cloud formation, as well as high phorophyte abundance and diversity implying large variation in bark roughness, moisture retention capacity, and pH. The slightly bimodal distributions of saxicolous and terricolous lichens were depressed at the elevational maximum of corticolous lichens.
Although the tripartite terricolous lichen Nephroma arcticum is easily accessible to lichen-feeding gastropods, grazing marks are mainly restricted to localized cephalodia with N-fixing Nostoc. We tested if this gastropod preference for cephalodia can be explained by differences in carbon based secondary compounds (CBSCs) in cyanobacterial versus green-algal tissues. CBSCs were non-destructively removed from air-dry thalli by 100% acetone. Compound deficient and control thallus parts were offered to the slug Arion fuscus and grazing preferences were quantified by area measurements in ArcGIS™. The concentrations of CBSCs (phenarctin, usnic acid, nephroarctin and methyl gyrophorate) in thallus parts with and without cephalodia were quantified with HPLC. Compared to purely green-algal parts, cephalodial parts with adjoining fungal tissues contained less defensive compounds, and were preferred by A. fuscus. The cephalodia themselves do not contain any CBSCs. After acetone rinsing, A. fuscus did not discriminate between green-algal and cyanobacterial parts. The results were consistent with the hypothesis that CBSCs in green-algal parts of N. arcticum play a herbivore-defensive role. It is further hypothesized that grazing of cephalodia may lead to N-starvation and reduced growth of N. arcticum thalli in southern portions of its range where lichenivorous gastropods are more abundant. This may play a role in shaping the southern distribution limit of this arctic-boreal lichen species.
Alectorioid and foliose lichens were weighed from full-size branches of Picea abies cut at two canopy heights in 100 trees in an old subalpine forested area in eastern Norway. The mean lichen biomass per branch decreased from 46 to 37 g moving upwards from 2–3 to 5–6 m canopy height. The lichen biomass correlated strongly with branch size variables, branch diameter alone explaining 48 of the variation in lichen biomass per branch (n=200). The alectorioid/foliose biomass ratio increased from 0·149 at 2–3 m to 0·316 at 5–6 m. Site factors reflecting openness of the canopy were computed for the branch at 2–3 m in all trees. The alectorioid/foliose biomass ratio increased significantly with the indirect site factors, suggesting that light, or factors associated with light, determine the balance between these two growth forms in tree canopies. Within the alectorioid biomass component, genera with usnic acid (Alectoria, Usnea) decreased with height, whereas the genus Bryoria with melanic pigments increased. According to the literature, dark melanic pigments have higher visible light screening efficiency than the yellowish usnic acid. Such patterns suggest a functional role for cortical pigments in the niche differentiation of alectorioid lichens.
Usnea is a species-rich and widespread lichenized fungal genus of well-lit parts of forest canopies (Motyka 1936, 1947; Clerc 1998). The bright greenish colour of these beard lichens reflects the presence of usnic acid in the cortex, which forms a thin, but dense sleeve around the trebouxioid photobiont in the outermost parts of the medulla. Usnic acid, a widely distributed dibenzofuran derivative produced by various mycobiont genera, strongly absorbs UV-B, but also the shortest PAR wavelengths (e.g. McEvoy et al. 2006, M. McEvoy, K. A. Solhaug and Y Gauslaa unpublished). Depending on species (Halonen et al. 1998), Usnea also contains a wide range of UV-B absorbing depsidones and depsides, though these are usually assumed to be confined to the medulla. Quantitative data on lichen compounds are rare in Usnea species, particularly with respect to the intrathalline variation.
Thalli of Lobaria pulmonaria of different sizes were collected from the trunks of two specimens of Populus tremula. The secondary lichen compounds, stictic, constictic, norstictic, peristictic, cryptostictic and methyl stictic acid were quantified by HPLC and ranked in order of decreasing concentration. There was a highly significant positive correlation between thallus size and the total concentration of secondary compounds, as well as the total content per unit area for specimens from the two sampled trees. According to hypotheses inferring a herbivore deterrent role of secondary lichen compounds, small, juvenile thalli should be more susceptible to herbivores than larger thalli. Thus herbivory might limit survival of young specimens in habitats rich in lichen-feeding molluscs and thereby reduce reproductive success.
Lichens are colourful organisms owing to numerous combinations of algal and fungal pigments (as reviewed by Rikkinen 1995). Colour is often used in taxonomic studies to aid species identification but it is sometimes over-used as a characteristic to discriminate related genera such as, Xanthoparmelia and Neofuscelia (Poelt & Leuckert 1993). However, colour variations within species can be significant (Solhaug et al. 2003) because of spatial (Gauslaa & Solhaug 2001; Gauslaa & Ustvedt 2003) and temporal variations (Gauslaa & McEvoy 2005) in environmental factors. There are few experimental studies on lichen colours so far; as a result we do not know the relative importance of genetic versus environmental factors. Our study aimed to assess the effect of ultraviolet radiation (UVR) on the colour of the widespread foliose lichen Xanthoparmelia stenophylla (Ach.) Ahti & D. Hawksw. (until recently known as X. somloensis (Gyeln.) Hale, see Ahti & Hawksworth 2005). Usnic acid is responsible for the yellowish appearance of its upper cortex, but other colour variations are also mentioned in taxonomic literature (Brodo et al. 2001). More specifically, we wanted to discover if UVR and the photosynthate ribitol supplied by the photobiont would cause changes in pigmentation in a Xanthoparmelia species. These factors have been shown to induce and stimulate the synthesis of the orange parietin in Xanthoria parietina (Solhaug & Gauslaa 2004; Solhaug et al. 2003).
Two shade-adapted (Lobaria pulmonaria and Cetraria islandica) and two sun-adapted lichen populations (Xanthoria parietina and Cetraria nivalis) were exposed to three irradiance regimes (1: photosynthetic radiation—PAR, 2: PAR+UV-A, 3: PAR+UV-A+UV-B) and two hydration regimes (1: no hydration, 2: daily hydration) in a growth cabinet for three weeks. Shade-adapted thalli had transparent upper cortices without coloured pigments, whereas sun-adapted thalli had coloured UV-B absorbing cortical pigments masking the photobiont. Manipulation of pigment concentration was the third factor used in the factorial design (1: pigments intact, 2: pigments non-destructively extracted from air-dry living thalli by acetone). Inhibition of the photobiont due to PAR alone was severe in the two shade-adapted populations, but no applied UV wavelength bands caused additional aggravation of photoinhibition. Shade-adapted thalli of the ubiquitous C. islandica were more PAR-susceptible than of the rare old forest lichen L. pulmonaria, suggesting that screening by the mycobiont rather than photobiont characteristics, account for their different success in sun-exposed localities. Hydration of shade-adapted species during exposure reduced their photoinhibition substantially, probably because of moisture-activated repair mechanisms. On the contrary, the sun-adapted X. parietina was most phototolerant in the desiccated state, whereas hydration caused increased photoinhibition. When removing the orange cortical pigment parietin, the photoinhibition in moist thalli was aggravated, confirming a PAR-protective function of parietin. No effects of irradiance treatment, pigment extraction (usnic acid), or hydration level were observed in C. nivalis.