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Morphology, reproduction and water relations - A system of morphogenetic interactions in Parmelia saxatilis
... The development of a dense cover of isidia, however, causes many interesting modifications at the thallus level. The large increase in surface area, for instance, modifies thallus water absorption (Rikkinen 1997) and water holding capacity (Jahns 1984), while the darker colour typical of isidial outgrowths probably influences the thermal operatingenvironment (Kershaw 1983;Coxson et al. 1984). ...
... In our opinion, this series of events is not confirmed by the limited iconography reported. In contrast, the importance played by medullary hyphae in isidium formation can be inferred from Jahns (1984), who holds that in Parmelia saxatilis (L.) Ach. isidia appear not in corticated areas, but in the crevices of the pseudocyphellae, i.e. ...
... These observations can be explained by two non-mutually exclusive hypotheses. Either isidia are less effective in securing the establishment of new thalli, probably because they are less efficient in dispersal and in the first stages of fixation to the substratum (Jahns 1984;Kärnefelt 1990;Scheidegger et al. 1995a;Zoller et al. 2000) and/or the morphogenetic events leading to the formation of isidia are more complex, being under the control of a larger number of genes. The latter hypothesis seems to be the less supportable: isidia are known from many unrelated taxa, and isidiate species often have close relatives without isidia (Bowler & Rundel 1975). ...
The development of isidia in thalli of Pseudevernia furfuracea from the Carnic Alps (North-eastern Italy), and the effects of these structures on CO. gas exchanges were investigated. The ontogenetic events were studied by comparison of sections stained with different histochemical tests and SEM observations. A high cell turnover rate in both symbiotic partners is the first sign of isidium. development, followed by an increased aplanosporogenesis of algae and growth of neighbouring medullary hyphae which become oriented upwards. Large nuclei and an intense cytoplasm activity characterize the mycobiont cells. The surface of very young isidia shows an irregular structure of spherical to ovoid protruding tips of perpendicular cortical hyphae, that are later organised in a pseudomeristematic area similar to that observed in the apex of growing lobes. CO2 gas exchange measurements carried out in the laboratory confirmed the high metabolic activity of isidia. At optimal water content and favourable light conditions, isolated isidia had rates of gross photosynthesis and dark respiration that were twice those of non-isidiate lobes. Isolated isidia also had a very low CO2 saturation point, probably because of their favourable surface/volume ratio, and a high light saturation, probably linked to their high content of photosynthetic pigments. The different roles played by isidia in the biology of Pseudevernia furfuracea, and particularly their rejuvenating effect on aged lobes, are discussed, and the presence of thalloconidia is briefly mentioned.
... Biomass was expressed as µg g -1 dw and mw. To obtain moist weights, the sample of hydrated lichen was blotted using bibulous paper to remove all surface-absorbed water before weighing (Jahns 1984, Anderson 2014). In addition to the five samples used to enumerate microbiota, five additional samples of thalli (10 all-totaled) were taken for the purpose of investigating the relationship between moist weight and dry weight among the three different sections. ...
... Currently, water relation in lichens is not fully understood, but there is good evidence that much of the absorbed water is accumulated in the hyphae, leaving gaseous, perhaps more hydrophobic spaces among the hyphal strands (e.g. Jahns 1984, Honneger et al. 1996. Water translocation within the thallus is driven largely by water potential gradients, especially during wetting and drying (Honneger 1991(Honneger , 2008. ...
Lichens are widely recognized as important examples of a fungal-algal or fungal-cyanophyte symbiosis; and in some cases they are a major food source for some animal grazers such as caribou (Rangifer tarandus), especially in the Arctic during winter. However, relatively little is known about the ecology of their co-associated bacterial and protistan communities. This is one of the first reports of an analysis of microbial communities associated with rock-dwelling foliose lichens (Flavoparmelia sp.), including a more detailed analysis of the microbial communities associated with segments of the shield-like, radially arranged lobes. Samples were taken from lichens on granite boulders beneath an oak and maple tree stand on the Lamont-Doherty Earth Observatory Campus, Palisades, N.Y. The bacteria and protist members of the lichen associated microbial communities are comparable to recently reported associations for foliose lichens growing on tree bark at the same locale, including the presence of large myxomycete plasmodial amebas, heterotrophic nanoflagellates, and naked and testate amebas. To obtain evidence of possible differences in the microecology of different portions of each radial lobe, three segments of the radial lobe in the shield-like lichen were sampled: 1) inner, more mature, central segment; 2) middle section linking the central and peripheral segments; and 3) outer, peripheral, usually broader, less closely attached segment. The mean densities (number/g) and biomasses (μg/g) of bacteria and heterotrophic nanoflagellates were highest in the older central segment and lowest in the peripheral segment of the radial lobes, especially when expressed on moist weight basis. Large myxomycete plasmodial amebas were typically located in the outermost segment of the radial lobe. The proportion of vannellid amebas (Vannella spp. and Cochliopodium spp.) were significantly more abundant in the samples of the inner lobes compared to non-vannellid amebas that were more prevalent in the outer lobes. The outer segment of the thallus lobe was typically more spongiose and absorbed more water per unit weight (based on a wet/dry-weight ratio) than the innermost segment. In general, patterns of densities and taxonomic composition of bacteria and eukaryotic microbes intergraded from the inner most segment to the outer part of each lobe-indicating a possible microecological gradient, coincident with the age-related and morphological radial gradations of the lobe. Overall, the evidence shows that the radial variation in the morphology and age-related variables of the three lobe segments may affect the microenvironment of the lobe segments and hence influence the organization of the microbial communities within each segment.
... The response of individual lichen species to this dilemma reflects the form of water available, the microenvironmental conditions in the lichen habitat and the physiological characteristics of the lichen species. Several studies have implicated the internal anatomy and the structure of the thallus with water relations and gas exchange (Rundel J 982; Larson 1983; Jahns 1984; Sancho & Kappen 1989; Palmer & Friedman 1990; Scheidegger et al. 1995; Valladares 1994; Valladares et al. 1993 Valladares et al. , 1994 Valladares et al. , 1998). These studies reveal that these ecophysiological processes become increasingly differentiated between zones within the same thallus that are of different age or different location. ...
... In this context, the thicker upper cortex and medulla exhibited by large thalli must play a role in protracting water loss, as indicated by the longer duration of the period of thallus hydration of the small thallus fragments of large specimens. These structural features have been implicated by numerous works (Snelgar & Green 1981; Jahns 1984; Rundel 1988; Sancho & Kappen 1989; Sancho et al. 1994; Valladares & Sancho 1995) in the control of thallus water economy. Additionally, the role of morphology must be also considered. ...
The influence on uptake and water loss of the structural changes experienced by Parmelia acetabulum during thallus development were investigated. Small specimens were characterized by flat lobes and a thin thallus and cortex. Large specimens appeared strongly rugose, imbricate and irregularly folded, and had a significantly thicker cortex and medulla than small thalli. Maximum water storage capacity did not differ between large and small thalli, although water retention was much higher in large thalli, presumably due to the interaction of structural characteristics and a higher boundary layer resistance. This translated into a longer duration of the period of thallus hydration in large thalli compared to small thalli. Incubation of thalli in water-vapour-saturated atmospheres induced full recovery of photosynthetic electron transport to the values before desiccation in small thalli but only induced a partial recovery in large thalli. The close correlation between photosynthetic electron transport and net photosynthesis during desiccation found in this species suggested that carbon-fixation activity could be regained to a larger extent by incubation of thalli in water vapour in small compared to large thalli. The higher ability for water vapour uptake of small thalli might allow them to efficiently use small amounts of intermittently available water or periods of high relative humidity. The significance of this differential ability to utilize water is discussed with regard to the known ecological preferences of the species.
... The speed of recolonization is an important factor in competition. Examples of such regenerative processes have been described several times (Jahns, 1984;Jahns & Ott, 1990;Jahns & Schuster, 1981). ...
... Since the small lobes are already fully differentiated they can grow directly into a new thallus. The liehen avoids the difficulties of propagation by isidia, äs isidia usually must degenerate into an undifferentiated lump of tissue, before a new thallus can be formed (Jahns, 1984). Lobes which have already developed on the parent thallus maintain a distinct advantage in time of development compared with competing species. ...
OTT, S., TREIBER, K. & JAHNS, H.M., 1992. The development of regenerative thallus structures in lichens. To be successful in their symbiotic relationship lichens have developed generative and regenerative thallus structures. Examples of the latter include isidia and soredia. In connection with the fact that construction principles in the lichen thallus are limited and that there is a comparatively small energy yield gained in lichen photosynthesis, a multifunctionality of morphological processes can be expected. The isidia of Parmelia crinita and Pseudevernia furfuracea and the vegetative propagules of Lobaria pulmonaria, which are sometimes referred to as isidia and sometimes as soredia, were investigated. Examination of the three species has shown that the classical distinction between soredia and isidia is not adequate for the description of the complex heterogeneity of vegetative diaspores. Especially during ontogeny, structure and function may change. The regenerative thallus structures showed a distinct multifunctionality. This multifunctionality implicates a complicated regulation system but details of the complex regulation processes are completely unknown.
... These newly formed lobes overgrow the senescent areas of the mother thallus which becomes, with increasing age, a multilayered structure. Dead lobes supporting new growth play an important role in thalline water relations (Jahns, 1984). Examples of this growth t\'pe are Parmelia saxatiUs (L.) Ach. ...
... Examples of this growth t\'pe are Parmelia saxatiUs (L.) Ach. (Jahns, 1984) or P. sulcata Taylor (Fig. 5 a). ...
Lichen-forming fungi are a large, taxonomically diverse group of nutritional specialists which acquire fixed carbon from a population of minute green algal or cyanobacterial cells. Mycobionts of foliose or fruticose lichens differ from the rest of the fungi by expressing morphologically and anatomically complex symbiotic phenotypes. The extracellularly located photobiont cell population of these macrolichens is housed and controlled by the quantitatively predominant fungal partner which competes for space above ground, secures adequate illumination and facilitates gas exchange. This review summarizes data on the ontogeny, functional morphology, growth patterns and internal thalline differentiation of macrolichens.
... The ability to hydrate from humid air might therefore not qualify, but in hydrating from liquid water sources (rainfall, dew, fog), the lichenized alga will often have a distinct advantage over a simple layer of free algal cells on the substratum. The elaborate surfaces, tissues, and hydrophilic wall materials of the lichen thallus are functionally adapted to specific strategies of moisture condensation, absorption, and retention (Larson and Kershaw 1976, Larson 1979, 1981, Jahns 1984, Valladares 1994, Pintado et al. 1997, Esseen et al. 2015. Thallus structure also elevates and more efficiently displays its phycobiont population to incident light, even in crustose forms (e.g., Vondrák and Kubásek 2013 ). ...
Lichens are classic examples of symbiosis, but some biologists have questioned whether the algal partner benefits from the relationship. Among the diverse lichen symbioses, the carbon transfer systems show remarkable convergences. When a compatible fungus is encountered, the alga proactively releases large amounts of carbohydrate, suggesting active participation rather than victimhood. Some lichen-related fungus–alga symbioses appear obligatory for the algal partner. Within true lichens, algal symbionts can persist at microsites where they might not otherwise be competitive, because of improved stress tolerance, reduced photoinhibition, protection from herbivores, and the more efficient moisture management and positioning for light interception that fungal structures provide. Algal clones continually disperse from the lichen thallus by diverse means, allowing the genotype to pioneer aposymbiotic colonies from a stable refuge. Because lichen-forming fungi conserve rather than consume their algal symbionts, the mutual self-interests of both partners substantially align in the stressful microhabitats where lichens are successful.
... Those isidia that are easily detached may serve, like soredia, as vegetative diaspores (Honegger 1987a;Scheidegger 1995;Zoller et al. 2000), while the basal scars left upon the thallus may aid in CO 2 diffusion, as do pseudocyphellae. Sturdier, less easily detached isidia increase thallus surface area for photosynthesis and condensation, absorption or external storage of moisture (Jahns 1984;Rikkinen 1997;Tretiach et al. 2005); they may also allow more efficient assimilation of CO 2 (Tretiach et al. 2005). Such isidia permit the lichen to take at least partial advantage of three-dimensional space for additional access to light, carbon and/or moisture resources, on a more limited scale than fully fruticose thalli but without relinquishing the extensive contact with substratum resources enjoyed by the underlying thallus. ...
Porina is a widely distributed, species-rich genus of crustose, lichen-forming fungi, some with thalline outgrowths that have been recognized as isidia. We studied three taxa with thalli consisting chiefly of ascending isidioid structures occurring on trunks and branches of Taxodium in southwestern Florida, and provide details of their structure with light and electron microscopy. Two of these taxa we describe as new species: P. microcoralloides and P. nanoarbuscula . Genetic sequences (mtSSU) suggest that they are closely related to each other, yet they differ markedly in the size, morphology and anatomical organization of their isidioid branches as well as in the length of their ascospores. In the three Floridian taxa studied, the crustose portion of the thallus is partly endophloeodic and partly superficial, the latter often patchy, evanescent or inconspicuous, and completely lacks the differentiated anatomical organization characteristic of the isidioid structures arising from it. In Porina microcoralloides , the ascendant thallus consists of branched, coralloid inflated structures with phycobiont ( Trentepohlia ) unicells arranged at the periphery of a loose central medulla. Sparse fungal cells are interspersed and overlie the algal layer in places, but no differentiated cortex is present, leaving phycobiont cells more or less exposed at the surface. In the closely related Porina nanoarbuscula , the isidioid structures are much finer, more densely branched, and composed of a single, central file of roughly spherical Trentepohlia cells surrounded by a jacket of subglobose fungal cells. The ascospores of P. microcoralloides are more than twice the length of those of P. nanoarbuscula . Although thalli of these two Porina species occur in the same habitats and are sometimes found growing alongside each other, phylogenetic analysis of rbcL sequences suggest that they partner with distinct clades of Trentepohlia phycobionts. A third taxon examined, Porina cf. scabrida , is morphologically rather similar to P. microcoralloides , but the ascendant branches are bright yellow-orange, more cylindrical, and corticated by a thin layer of agglutinated fungal hyphae; perithecia were not seen. Analysis of mtSSU sequences places it distant from P. microcoralloides and P. nanoarbuscula phylogenetically. None of the Floridian taxa studied was particularly close to the European isidiate species Porina hibernica and P. pseudohibernica , which appeared as sister to each other in the analysis. While a particular type of isidiose structure may be reliably characteristic of specific taxa, similarities or differences in these structures do not seem to be useful indicators of phylogenetic proximity or distances among taxa. The morphological trends evident in Porina suggest that multiple transitions from crustose to isidioid or microfruticose growth have arisen repeatedly and in quite different ways within this single genus. At least some of the diverse structures treated within the broad concept of isidia may be representative of the developmental pathways by which fruticose growth forms may arise.
... Such leaf-like architecture is well adapted to harvesting low light. At the same time, many foliose lichens can acclimate to high-light situations by increasing thallus thickness (Longinotti et al., 2017) and/or by forming overlapping layers (Jahns, 1984). ...
Tree-dwelling hair lichens in the genus Bryoria provide crucial late-winter forage for Deep-Snow Mountain Caribou (DSC), an imperiled ungulate endemic to south-central British Columbia, Canada. Because DSC survival requires continuous access to heavy hair lichen loadings, conservation efforts can benefit from an improved understanding of the factors that contribute to such loadings. Here we quantify the relation of Bryoria abundance to stand spacing by testing an "Angle-To-Canopy-Skyline" (ATCS) protocol as a measure of stand openness and a proxy for ventilation. Fieldwork conducted in 60-year-old conifer forests on a 250-m conical volcano within the range of DSC yielded three principal findings: (1) Bryoria abundance strongly increases with increasing stand openness; (2) Pinus contorta supports much heavier Bryoria loadings than other local host trees; and (3) ATCS is a powerful predictor of arboreal hair lichen abundance in general across a wide range of environmental settings, but does not predict the abundance of foliose lichens. We suggest that canopy openness, at least within the range of DSC, complements stand age as a key factor in the development of heavy Bryoria loadings, consistent with the hypothesis that Bryoria benefits from rapid drying after rain. The possibility that anomalously high Bryoria abundance on Pinus may hold promise for accelerated DSC habitat restoration following clearcut logging is explored but rejected.
... Such leaf-like architecture is well adapted to harvesting low light. At the same time, many foliose lichens can acclimate to high-light situations by increasing thallus thickness (Longinotti et al., 2017) and/or by forming overlapping layers (Jahns, 1984). ...
... and Pseudevernia furfuracea reveal patterns of increasing isidia cover in more exposed microclimates, such as higher in tree canopies or on south-facing slopes (Martínez et al., 2012(Martínez et al., , 2014Rikkinen, 1997) where temperature fluctuations are more extreme and rain and dew more abundant. From a hydrological perspective, isidia increase thallus surface area, thereby increasing water-holding capacity (Jahns, 1984), slowing desiccation and reducing suprasaturation depression of photosynthesis (Tretiach et al., 2005). If these phenomena translate to interspecific variation at the macroscale, this could provide some explanation into why isidiate lichens are more frequent in warmer, wetter habitats. ...
Aim
Functional traits offer a window into how organisms are adapted, and might acclimate, to environmental pressures. Despite being important in ecosystem function, lichens are underrepresented in trait-based research; understanding how lichen functional traits vary with climate and habitat availability will be useful in predicting how communities will respond to climate change, for example, in wetter and warmer boreal and arctic ecosystems. Here, we assess the influence of macroclimate and forest availability on the spatial distribution of lichen traits across Norway.
Location
Norwegian mainland.
Taxon
Lichens.
Methods
We used relative trait frequency (RTF) data from LIAS gtm, a database combining trait information from LIAS (A Global Information System for Lichenized and Non-Lichenized Ascomycetes) and GBIF (Global Biodiversity Information Facility) species observations. The 20 traits included photobiont types, growth forms, cortical features and reproductive modes. Nonparametric multiplicative regression (NPMR) models were used to explore the relationships between the environmental predictors of precipitation, temperature and forest availability.
Results
All traits showed significant relationships with the three environmental predictors. Photobiont type and reproductive mode traits produced the strongest models and revealed ecologically meaningful biogeographical patterns. Trebouxioid species peaked in colder, drier upland regions, while trentepohlioid lichens displayed an affinity for wetter and warmer climates and had a western and southern distribution. Cyanolichens increased with increasing precipitation and were strongly coastal. Sorediate and isidiate lichens were positively related to temperature, the former also increasing with forest cover. The above responses were consistent with the physiological and habitat requirements of the associated lichens. The remaining traits had weaker responses.
Main conclusions
Discrete traits (i.e. photobiont type and reproductive mode) with relatively low ecological plasticity reflect clear functional environmental responses at the large scale. By contrast, growth form and thallus structural features—proxies for continuous variables—are too variable within each given category to show observable distribution patterns.
... The morphological characteristics of lichen species are considered important in the evaluation of pigments and metals. The roughness and wrinkling of the outer surface are known to affect the accumulation of elements in the lichens (Bargagli and Mikhailova 2002), as well as the presence of symbiotic propagules, since they increase the rates of gas exchange (Tretiach et al. 2005) and water retention on the lichen thalli (Jahns 1984). The fine particles might interfere in the species physiology in different ways, displacing macronutrients from the cell wall, carrying pollutants inside the cells and changing the pH (Branquinho et al. 2011;Bergamaschi et al. 2007). ...
Anthropic activities such as the emission of pollutants resulting from industrial and agropastoral activities promote several changes in urban and forest areas. Lichens are organisms that are used in air quality evaluations due to their sensitivity to these changes. The aim of this study is to analyze the presence of morphophysiological damages and the metal concentration in samples of the lichen Parmotrema tinctorum, in urban and forest areas, checking for possible parameter variations between these areas, in the different matrices and seasons in the Southern region of Brazil. Six areas were selected (urban and forest), assigned to the rural/urban and urban/industrial matrices belonging to the watershed of the Rio dos Sinos, Brazil. The following parameters were analyzed: Index of photobiont vitality (IPV), photosynthetic pigments (chlorophyll, carotene, and pheophytin) and metals (Cu, Cr, Zn, Pb, and Ni) in the thallus of the lichen. The data were analyzed by an ANOVA one way, Pearson correlation test, and principal component analysis (PCA). Variations in the morphophysiological parameters were recorded in all the areas revealing significant differences. The lowest IPV values and highest concentration of metals were recorded in the urban environment, while low chlorophyll levels were found in the forest areas. The PCA showed a distinction between the areas and the season. The level of urbanization, vehicle traffic, and the weather conditions might have influenced the results. The use of P. tinctorum, the index of photobiont vitality and chlorophyll and pheophytin content, has proved to be an efficient tool to diagnose the air quality in the areas analyzed, allowing its use as a model in air monitoring studies, both in urban and forest areas, as well as in distinct matrices in the subtropical region.
... Another aspect of the observed resistance to ionizing radiation is based on the very low water content of the anhydrobiotic lichen thallus, which is <5% of thallus dry weight under ambient conditions ( Jahns, 1984) and may be lower under extremely desiccating space or martian conditions. Ionizing radiation causes the radiolysis of water, which is the primary source of free radicals in cells, which subsequently and crucially damage cellular compounds (Riley, 1994;Kovács and Keresztes, 2002). ...
This study addresses the viability of the lichen Xanthoria elegans after high-dose ionizing irradiation in the frame of the STARLIFE campaign. The first set of experiments was intended to resemble several types of galactic cosmic radiation (GCR) as present beyond the magnetic shield of Earth. In the second set of experiments, γ radiation up to 113 kGy was applied to test the limit of lichen resistance to ionizing radiation. Entire thalli of Xanthoria elegans were irradiated in the anhydrobiotic state. After STARLIFE 1, the metabolic activity of both symbionts was quantified by live/dead staining with confocal laser scanning microscopy. The photosynthetic activity was measured after the respective irradiation to assess the ability of the symbiotic green algae to restore photosynthesis after irradiation. The STARLIFE campaign complements the results of the LIFE experiments at the EXPOSE-E facility on the International Space Station by testing the model organism Xanthoria elegans on its resistance to hazardous radiation that might be accumulated during long-term space exposure. In addition, the photosynthetic activity of metabolically active lichen was investigated after X-ray irradiation up to 100 Gy (3.3 Gy/min). Since previous astrobiological experiments were mostly performed with anhydrobiotic lichen, these experiments will broaden our knowledge on the correlation of physiological state and astrobiological stressors.
... c Factorial scores of samples, indicated with different symbols according to the three clusters (I, II, III) resulting from CA (Fig. 1b), and to lichen variety. Paired samples of the two varieties at each site (numbers) are connected by solid lines representing Euclidean distances in the PC space holding capacity (Jahns 1984) of a lichen thallus. The efficient dispersal by isidia (Purvis et al. 1992) makes the presence of such structures a very common trait in P. furfuracea, while a considerable morphological variability has been related to specific, different ecological contexts (Rikkinen 1997). ...
The epiphytic lichen Pseudevernia furfuracea is widely used as biomonitor of airborne trace elements and other contaminants and consists of two taxonomic varieties (var. furfuracea and var. ceratea). Here, we assessed the occurrence of inter-varietal differences in the elemental composition of paired samples of var. furfuracea and var. ceratea collected in 20 remote sites of Italian mountains. The concentration of 40 elements was measured by inductively coupled plasma mass spectroscopy, after digestion with HNO3 and aqua regia. The magnitude of inter-varietal differences compared to the effect of large-scale site-dependent environmental factors (i.e., lithological substrate, host tree species, and altitude) on overall element content was explored by multivariate analysis techniques and tested by generalized linear mixed modeling (GLMM). Further GLMMs were separately fitted for each element testing taxonomic-related variability against uncertainty associated to the analytical procedure. Inter-varietal differences were statistically significant only for Hg and P, with higher content in var. ceratea at most sites, and for Mg and Zn, showing the opposite pattern. Since the elemental composition of P. furfuracea in remote sites was mostly affected by local lithology and climatic conditions, our results confirm that lichen material for active biomonitoring should be collected in a single ecologically homogeneous remote area. We also indicate sites in the Eastern Alps where P. furfuracea showed the minimum content of most elements, which are suggested as locations to collect lichen material for transplants. Besides the context-dependency at large spatial scale, variations of elemental composition apparently related to taxonomy, could possibly be due to unequal incidence of morphological traits of the collected material. Further research is needed to clarify this issue, and how it affects bioaccumulation phenomena.
... Although, to our knowledge, its relation with climate has not been directly addressed, a work with Lobaria pulmonaria (L.) (Mart ınez et al. 2012) showed a higher frequency and abundance of isidia upon tree trunks closer to the canopy, where microclimatic conditions are harsher (higher radiation and temperature, lower humidity). Some authors have pointed out that important changes may occur in species with a dense cover of isidia (Jahns 1984). More isidia cover could modify thallus water absorption (Rikkinen 1997) and water-holding capacity (Tretiach et al. 2005) in a way similar to trichomas in plants. ...
Climate change is expected to cause several impacts at the global scale, and drylands will be amongst the most affected areas. Thus, investigating how these changes will affect the composition, structure and functioning of dryland ecosystems has become a priority. From an ecological indicator point of view, several works have shown that functional diversity is better than species richness to understand ecosystem functioning or response to environmental factors. However, most of these works focus on plants, while those of other organisms remain largely unknown. Lichens are amongst the ecosystem components more sensitive to climatic changes due to several physiological and ecological characteristics. Their poikilohydric nature (therefore highly dependent on the atmosphere for water supply) and their ubiquity on terrestrial ecosystems underlie their potential as indicators of climate. Nonetheless, works specifically aiming to identify lichen functional traits that respond to aridity remain poorly explored, particularly in drylands.
We proposed to identify lichen functional traits and respective functional groups responding to aridity in a Mediterranean drylands ecosystem.
Lichen diversity was sampled in open holm oak woodlands along an aridity gradient in SW Europe (Iberian Peninsula). Lichen functional traits that could be easily identified and related to water uptake were selected to be tested: type of photobiont, growth form and reproduction strategy.
Lichen species composition was related to the aridity gradient. The three traits chosen were related with the community's response to aridity, but with contrasting responses in different functional groups. More specifically crustose and fruticose lichens, isidiate species and the ones with Trentepohlia as photobiont were related to the less arid part of the gradient. Foliose species and cyanolichens, on the contrary, were associated with the most arid areas.
Synthesis. We were able to identify lichen traits responding to aridity. Type of photobiont was particularly responsive, with Trentepohlia and cyanobacteria functional groups, responding clearly in contrasting ways to aridity in this drylands ecosystem. This work emphasizes functional diversity role on understanding and assessing the response to environmental factors, namely to climate. It also highlights the potential use of lichen functional groups as ecological indicators of climate change.
... Further evidence for an ecological explanation of soredia production in I. splachnirima is the restoration of apothecial growth by altered environmental conditions (Fig. 4) and the partly multi-layered thallus architecture resulting from new lobules growing out of soredia (Fig. 5). That growth pattern is beneficial for water economy (Jahns 1984), and could implicate photo-stress and/or desiccation as possible triggers for the inhibition of apothecial development and the formation of soralia. The occasional production of marginal soralia in addition to apothecia is also known in Trapeliopsis colensoi (C.Bab.) ...
Marginal soralia and occasional conidiomata are reported for the first time in populations of Icmadophila splachnirima (Icmadophilaceae) from southern New Zea-land. Ecological implications are discussed, and an emended description is given.
... Hancock & Seppelt (1988) suggested that lichen species might exhibit niche specificity related to moisture availability. Size, morphology and anatomy of the lichen thallus may influence the rates of water uptake and loss (Larson & Kershaw 1976, Larson 1979, Jahns 1984, Harrisson et al. 1986, Hancock & Seppelt 1988, Sancho & Kappen 1989, Hestmark 1992). In some of these studies size and shape of the thallus were determined using morphological or anatomical parameters or more elaborate methods to determine surface to weight ratio (Larson and Kershaw 1976, Larson 1979). ...
Uptake and loss of water by six lichen species from the Argentine Islands, Antarctic Peninsula, were studied in their natural habitat and in laboratory studies. Under field conditions, during a period of rain, uptake of moisture ranged from 15% d w h1 in Umbilicariadecussata to 38.8% in M.tesselata. A comparison of thalli of M.tesselata from the shoreline with thalli collected further inland showed significant differences in maximum water content and in rates of water loss and uptake between thalli from these sites, which could be ascribed to the presence of salt in the thalli of M.tesselata from the shore. Thallus samples of Usneaantarctica collected from an exposed site showed lower uptake rates and higher loss rates of water than samples collected from a more sheltered site. Under laboratory conditions the maximum moisture content ranged from 67% in Usneaantarctica to 391% in M.tesselata. Exposed to an atmosphere of c. 40% relative humidity and c. 15°C, lichen thalli lost their water during the first hour of the experiment at rates ranging from 34% of the maximum moisture content in Umbilicariapropagulifera to 70% in U.decussata. Rates of water loss diminished with time, and after 416% of thallus dry weight. The microclimate is the driving force for the thallus water regime. Specific differences in rates of water loss and water uptake depend on the morphology and anatomy of the lichen thalli. The results of the laboratory experiments agree with those from the field study. However, local differences in microclimatic or other environmental factors can be responsible for significant differences in the water regime of thalli of the same species, a result which can only be obtained from field studies.
... Therefore, for some poikilohydric plants, structural and physiological acclimations to sun and shade sites could exhibit a pattern which is the reverse of that observed in vascular plants regarding light harvesting. Lichens were found to overcome short periods of activity by increasing maximum rates of net photosynthesis (Groulx and Lechowicz, 1987) or by means of morphological and 0305-7364\97\090345j09 $25.00\0 bo970453 # 1997 Annals of Botany Company anatomical adaptations which improve water storage and retention (Rundel, 1974 ;Larson and Kershaw, 1976 ;Larson, 1979Larson, , 1981Snelgar and Green, 1981 ;Jahns, 1984 ;Sancho and Kappen, 1989 ;Valladares, 1994 ;Tretiach and Brown, 1995 ;Valladares and Sancho, 1995). Nevertheless, the role of some of these thallus structures in providing water storage capacity, and the actual location of water within the thallus are still matters of interest and debate (Valladares, Wierzchos and Ascaso, 1993 ;Honneger and Peter, 1994 ;Valladares, Sancho and Ascaso, 1997). ...
The present work analyses the morphology, anatomy, water relations and chlorophyll content of thalli of the lichenRamalina capitatavar.protectafrom two different populations exposed to contrasting microclimatic conditions due to differences in the orientation of the rock surface. The population on the north-facing rock surface (NFS) was exposed to lower photosynthetic photon flux densities (PPFD), remained at high relative humidities for longer periods of time and was exposed to lower temperatures than the population on the south-facing surface (SFS). We proposed the hypothesis that the shadier the habitat the greater the ecological advantage for enhanced light harvesting. Thalli from the SFS had shorter and wider lacinia, thicker thalli, mostly due to increased medulla thickness, a higher water-retention capacity, a higher percentage of thallus volume occupied by the algal cells and a higher chlorophyll content than thalli from NFS. The phenotypic plastic response of the traits studied inR. capitatavar.protectawas not directly related to differences in the light availability, at least for the range of PPFD experienced by the two populations studied, since the population exposed to higher PPFD exhibited larger amounts of light harvesting pigments. Both populations exhibited the same intrathalline distribution of algal cells and chlorophylls, which were more abundant in the apical than in the basal zones of all thalli studied. Periods of water-induced metabolic activity were shorter in the SFS than in the NFS, and structural and chlorophyll data indicated that thalli from the SFS were better prepared for the photosynthetic exploitation of these briefer periods and for maintaining thallus hydration into dry periods. These results suggest that differences in selective pressure between the two populations ofR. capitatavar.protectastudied involved maximization of the photosynthetic exploitation of the periods of metabolic activity when they are brief, as has been described for certain vascular plants from xeric environments.
... In this way, we can see similarities between the development of the M. sorediella organs described above and the growth processes of the isidia, pseudocyphellae and lobuli observed in Parmelia saxatilis (L.) Ach. (Jahns 1984), but in contrast to P. saxatilis, in M. sorediella the conidiomata development induces the process. ...
Lichen material from the Iberian Peninsula of Melanelia commixta, M. hepatizon and M. sorediella has been studied and compared on the basis of morphology, chemistry, habitat and distribution. The new combination Melanelia sorediella is proposed and Cetraria commixta f. sorediella is lectotypified. Chemotypes I and III have been detected in M. commixta. Melanelia sorediella is characterized mainly by the formation of pycnoisidia and soralia-like structures in the lamina and margins of the thallus and by the absence of pseudocyphellae and apothecia. The pycnoisidium is here described as a combination of isidia-like proliferations of the thallus surface containing pycnidia, carrying algae and acting as vegetative symbiotic propagules. Non detached pycnoisidia grow into lobuli in central parts of the thallus, regenerating it. Pycnoisidia, soralia-like areas and lobuli are formed as a consequence of pycnidia development. Melanelia sorediella is morphologically and chemically close to M. commixta and is currently known from mountains of central and south-west Europe where it grows on acid rocks. In south-western Europe, the meridional limit of the distribution of the three species studied seems to be located in the mountains of the central part of the Iberian Peninsula (Sistema Central Iberico). Relevant data on the three species are provided and a key is also included.
... In these experiments, although the rate of desiccation was controlled, P. laevigata rapidly lost water and achieved equilibrium water contents within 24 h (Table 1). Lasallia pustulata may be morphologically adapted to reduce the rate of water loss, as has been shown for a number of lichens inhabiting desiccating environments (Snelgar & Green 1981, Jahns 1984). The average density of pyrenoglobuli per jj.m2 of pyrenoid cross-sectional área was not significantly altered by any of the desiccation conditions tested, although it was slightly reduced by slow drying (Table 2 ). ...
Phycobiont cells of Parmelia laevigata contain chloroplasts with pyrenoids penetrated by a reticulum of tubules. The occurrence and significance of such tubules in algae is discussed. Although these tubules collapsed in desiccated cells, their lumen reappeared on rehydration. However, in such desiccated cells, pyrenoglobuli did not become peripherally located within the pyrenoid, except when damage occurred to the pyrenoid matrix. Rehydration of desiccated cells reduced the number of pyrenoglobuli per pyrenoid.
... The fixation, germination and establishment of symbiotic propagules have been described for various foliose and fruticose species Jahns 1988). Both sorediate species (Schuster 1985;Ott 1987c) and die isidiate Parmelia saxatilis disintegrate and form a basal tissue (Jahns 1984) tiiat has a considerably different organization than have the diaspores directly after dispersal. However, in P. pastillifera, the knob-like isidia keep their internal structure. ...
Vegetative diaspores of Lobaria pulmonaria were transplanted to previously uncolonized trees. The early development of the corticated but otherwise non-stratified isidioid soredia was studied mainly by low-temperature scanning electron microscopy. Anchoring hyphae developed from cortical hyphae after 2–4 months and later apical or lateral pseudomeristematic growth zones were formed. After 15 months the growth zones further differentiated into 0·5-mm-broad lobes and revealed a stratified thallus typical for this foliose epiphytic lichen species. The experiment showed that the small population size of L. pulmonaria was limited by the low reproductive potential of the species and that it might fail to compensate for a relatively high disturbance, natural or anthropogenic, in the stand.
... Unlike soredia, which are lighter and smaller and easily transported by small organisms such as ants ( Lorentsson and Mattsson, 1999), neuroptera ( Slocum and Lawrey, 1976), mites ( Stubbs, 1995), or by fluids such as air and water ( Armstrong, 1987Armstrong, , 1994Harmata and Olech, 1991;Marshall, 1996), phyllidia and isidia (other common vegetative propagules typical of the lichen symbiosis) are larger and relatively heavy, and therefore their dispersal is generally restricted to small distances ( Awasthi, 1983;Bjelland, 2001), although this has been questioned by several authors (e.g. Jahns, 1984;Kärnefelt, 1990). Slugs and snails are however sufficiently large to act as active, efficient carriers of these structures: when visiting the Peltigera thalli for food (or refuge: see Peake and James, 1967;Baur and Baur, 1997, and our obs.), ...
The intensity of grazing of two land snails, Cantareus aspersa and Limax sp., on three epigaeic species of Peltigera with (P. horizontalis, P. neckeri) and without (P. praetextata) secondary compounds, were studied in the field in three transects of 2×50 m along an altitudinal gradient in the surroundings of Pistoia (Tuscany, Italy). The results were confirmed by laboratory experiments and were carried also out on a further species lacking lichen compounds (P. degenii), showing that land snails definitely prefer thalli lacking lichen secondary compounds. Damage intensity is correlated to the thallus size of the lichens.
... Evolution through mutualistic co-operation may, in fact, better apply to fungus–green algae relationship as in some cases the evolution of lichenization is associated with the loss of capability to grow in axenic culture and some other morphological changes (Lutzoni and Vilgalys 1995). Moreover, the prerequisite of vertical co-transmission of symbionts in mutualistic co-evolution is best met in bipartite lichens with green algae as the only symbiont producing vegetative soredia that are largely regarded as the most efficient vegetative diaspores in lichens (Jahns 1984). In conclusion, we have treated here lichen fungus as an optimal harvester rather than a mutualistic partner. ...
Lichen symbiosis has been traditionally treated as a model case of mutualism in which both partners, the fungus and the photobiont, gain benefits reciprocally. Some recent evidence, however, supports an alternative view that lichen symbiosis may represent an association largely controlled by the commensal or even parasitic fungal partner. The latter gains photosynthates from the photobiont (algae and/or cyanobacteria) which may not always substantially benefit from the symbiosis. We analyze from this perspective how a lichen fungus may maximize photosynthetic gains in bipartite and tripartite associations. We treat the frequency of nitrogen-fixing cells called heterocysts in cyanobacteria and the relative proportion of green algal cells vs. that of cyanobacteria per unit fungus as the variables to be manipulated for maximal carbon gain. The model predicts that even with a negligible cost of cephalodia (compartments containing cyanobacteria) it is in the interest of the tripartite lichen, first, to increase the heterocyst frequency, and second, keep the relative number of cyanobacteria considerably lower than that of green algae. Hence, the lichen fungus achieves higher fitness by making the cyanobacterial partner to specialize on N fixation. The available empirical data support these predictions as the reported heterocyst frequencies in bipartite lichens range from 2 to 8%, and in tripartite lichens between 10 and 55%. It is concluded that interaction asymmetry (i.e. commensalism or parasitism rather than mutualism) provides a sound basis to understand the high phenotypic plasticity expressed by fungi-forming bipartite and tripartite associations with cyanobacteria and green algae.
... A high water loss rate, and therefore a low thallus resistance, prevails throughout the photosynthetically active thallus water range in D. plumbea. Highly contrasting water loss kinetics have been documented in Parmelia saxatilis (Jahns 1984). A high water loss rate even during later stages of a drying cycle (50% water content) could hardly be possible without an ecient translocation of water within the hypothallus felt. ...
Rosette-formed, circular thalli of Degelia plumbea were studied in the laboratory. Regardless of thallus size, the optimal quantum yield of photosystem II (F
V/F
M) remained at a high, constant level during a drying cycle starting with fully hydrated thalli until the thallus water content
reached about 200%. Net photosynthesis reached a maximum level at this hydration level. Thereafter, both F
V/F
M and net photosynthesis fell rapidly to zero at a water content of somewhat less than 100%. There was a highly significant,
positive relationship between thallus size and the water-holding capacity, as well as a strong, negative correlation between
size and water loss per thallus area. Consequently, an increase in thallus size from 1 to 36 cm2 lead to a tenfold prolongation of the photosynthetically active period during a drying cycle at a low radiation regime. The
improved water-holding capacity in larger thalli is mainly a result of a thicker hypothallus. The fast desiccation of small
thalli suggests that the regeneration of D. plumbea could be severely hampered by nearby logging that raises the evaporative demand by increasing radiation loads and wind exposure
at remaining lichen sites.
The pore system within the thalli of 13 lichen taxa belonging to the family Umbilicariaceae has been studied by means of mercury intrusion porosimetry. A characteristic bimodal pore size distribution with a central depression around 0.05 μm of equivalent pore radius was obtained in all lichen samples. However, clear differences were found among the pore size distributions of each lichen taxa. The total thallus porosity was undoubtedly related to the anatomy of the medulla. In general, a radial plectenchymatic medulla conferred larger porosity to the thallus than an arachnoidal one. Maximum thallus water content closely depended on the total thallus porosity in the five lichens possessing rhizinomorphs. The species with a similar type of medulla could be grouped together in a multivariate analysis that considered three porosimetric parameters and the maximum thallus water content. Umbilicaria cinereorufescens was the most distinct species, with the lowest values of total porosity and water storage capacity and the largest value of thallus density, apparently due to its scleroplectenchymatic medulla. The pore size distribution existing inside the thallus of the species studied is discussed in relation to the often opposing problems of CO2 exchange and optimal water relations. Some results pointed to a large influence of the micropores (<0.05 μm) on the water storage capacity of the thallus, while the macropores would have a more important role in gas exchange.
Species of Umbilicaria developed adventive lobes from the surface of rhizomorphs after the trapping of algae. Secondary lobes were formed mainly in older thalli and were thought to be important for propagation. Regeneration from the base of the umbilicus probably accounted important for the recolonization of the original site and for maintenance of the population.
We present a new approach to the study of the functional implications of thallus size and intrathalline variability in foliose lichens that combines quantification of structural features by means of stereology coupled with a range of physiological techniques (gas exchange, chlorophyll fluorescence and carbon isotope discrimination). The percentage of the thallus of Lobaria scrobiculata occupied by photobiont cells was significantly larger in marginal than in central thallus zones. Central zones were twice as thick as marginal zones but, surprisingly, their density was lower than that of the marginal zones. We developed a new and simple system to compare gas diffusion in marginal and central thallus zones. Large thalli of L. scrobiculata were exposed to different gases (ambient air and nitrogen) and the time response of the photobiont of different zones were followed in situ by chlorophyll fluorescence. Marginal zones responded faster indicating lesser diffusion resistances than in central zones. However, carbon isotope discrimination was similar in the two zones. This fact suggested that the activity of a carbon concentrating mechanism (CCM) in L. scrobiculata overrode the limitations to CO2 fixation imposed by large diffusion resistances. Photosynthetic lichen water use efficiency (LWUE) of marginal zones was significantly higher than that of central zones due to the combination of long water retention times with high photosynthetic rates. It is suggested that both water storage and gas exchange (usually opposing strategies in lichens) were maximized in the marginal zones of L. scrobiculata due to the operation of a CCM, which created a homogeneous CO2 environment across the thallus counter-balancing some of the structural intrathalline differences found in large individuals of this lichen.
A wide range of taxa in the higher ascomycetes (Pezizomycotina sensu Eriksson and Winka 1997) forms some sort of symbiosis with algae and cyanobacteria. These associations include fungal parasites on algae (Hawksworth 1987; Lewin 1995), mycophycobioses (Kohlmeyer 1967; Kohlmeyer and Kohlmeyer 1972), lichenicolous fungi (Hawksworth 1983, 1988a; Clauzade et al. 1989) and lichens (Nash 1996). Naturally, the delimitation of these associations is not clear and intermediate forms exist. However, an attempt to define these terms is made in Table 1, following Hawksworth (1988a). An exhaustive treatment on fungal-algal associations in the large order Lecanorales can be found in Rambold and Triebel (1992). This chapter concentrates on the morphology, phylogeny and classification of lichen-forming ascomycetes. Only a brief treatment can be given here and the reader is referred to other recent books for more information (e.g., Ahmadjian 1993; Nash 1996).
Mycobionts of the four lichen species Anaptychia ciliaris, Physcia tenella, Physconia distorta and Xanthoria parietina, which were grown for more than one year under axenic conditions, were then attached to twigs of Quercus robur. The mycelia were subsequently exposed to natural conditions for one year. The observations show, that the isolated lichen mycobionts remain viable over a very long period of time and under various conditions. The transplanted mycelia served as substrate for lichen diaspores and free-living algae. In addition symbiotic interactions occurred between the isolated lichen fungi and their photoautotrophic partner. The mycobiont of Physcia tenella in contact with free-living algae showed a transition from mycelial growth to the symbiotic state and free-living young lobules of this lichen colonized the transplanted mycobiont and became an integral part of it. Intrahyphal hyphae took part in this relichenization process.
Lichens are symbiotic organisms in which fungi and algae and/or cyanobacteria form an intimate biological union. This diverse group is found in almost all terrestrial habitats from the tropics to polar regions. In this second edition, four completely new chapters cover recent developments in the study of these fascinating organisms, including lichen genetics and sexual reproduction, stress physiology and symbiosis, and the carbon economy and environmental role of lichens. The whole text has been fully updated, with chapters covering anatomical, morphological and developmental aspects; the contribution of the unique secondary metabolites produced by lichens to medicine and the pharmaceutical industry; patterns of lichen photosynthesis and respiration in relation to different environmental conditions; the role of lichens in nitrogen fixation and mineral cycling; and the use of lichens as indicators of air pollution. This is a valuable reference for both students and researchers interested in lichenology.
The book embodies the detailed account about unique symbionts, i.e. lichens in
ecosystem monitoring. The fi rst chapter deals with the unique characteristic
features of lichens which facilitate their survival in extreme climates and
make them an ideal organism for ecosystem monitoring. Biosynthesis
of secondary metabolites is known to protect lichens against increasing
environmental stresses; therefore, the second chapter provides insight into
various chromatographic and modern spectroscopic techniques involved in
separation and characterisation of lichen substances.
The third chapter elaborates the criteria for selection of biomonitoring
species and characters of host plant that infl uence lichen diversity and detail
about different lichen species utilised for biomonitoring.
One can retrieve preliminary information about the air quality based on
the lichen community structure and distribution of bioindicator species as
lichen communities/indicator species provide valuable information about the
natural-/anthropogenic-induced changes in the microclimate and land-use
changes due to human activity. Therefore, for identifi cation of species, a key to
genera and species provides concise information to identify the lichen species
based on their morphological and anatomical characters and chemicals
present. Keys provided in Chap. 4 will help the beginners to identify some
common lichen species based on the distribution in different climatic zones
of India. The section also provides comprehensive information about the
bioindicator communities and bioindicator species from India.
Chapter 5 provides the details of factors affecting the ecosystem (natural
as well as anthropogenic disturbances), and the role of lichens in ecosystem
monitoring in India has been discussed in detail.
Chapter 6 discusses the need and utility of indicator species especially lichen
biomonitoring data in sustainable forest management and conservation.
The content about lichens in biomonitoring will be a valuable resource for
researchers from different fi elds and will provide an essential reference for
people interested in lichens and its role in ecosystem monitoring. The book
will also hopefully popularise lichenological studies in India and will generate
more active participation of lichen biomonitoring studies in management and
conservation of natural resources in India.
The influence on uptake and water loss of the structural changes experienced by Parmelia acetabulum during thallus development were investigated. Small specimens were characterized by flat lobes and a thin thallus and cortex. Large specimens appeared strongly rugose, imbricate and irregularly folded, and had a significantly thicker cortex and medulla than small thalli. Maximum water storage capacity did not differ between large and small thalli, although water retention was much higher in large thalli, presumably due to the interaction of structural characteristics and a higher boundary layer resistance. This translated into a longer duration of the period of thallus hydration in large thalli compared to small thalli. Incubation of thalli in water-vapour-saturated atmospheres induced full recovery of photosynthetic electron transport to the values before desiccation in small thalli but only induced a partial recovery in large thalli. The close correlation between photosynthetic electron transport and net photosynthesis during desiccation found in this species suggested that carbon-fixation activity could be regained to a larger extent by incubation of thalli in water vapour in small compared to large thalli. The higher ability for water vapour uptake of small thalli might allow them to efficiently use small amounts of intermittently available water or periods of high relative humidity. The significance of this differential ability to utilize water is discussed with regard to the known ecological preferences of the species.
The distribution of plants and the development of individuals at a certain location depend to a considerable degree upon microclimate.
This is true for phanerogams as well as for lichens. For lichens, however, crucial environmental influences occur on a much
smaller scale (Schöller 1991, Canters et al. 1991). The microclimate of a higher plant is defined by the environmental conditions that occur within an area of about 1 m2 around the plant. However, for lichens important changes occur within a few cm2. Lichenologists frequently refer to the microclimate of phanerogams as mesoclimate. This difference in scale of the microclimate
is the only difference, as the contributing features are identical for both groups of organisms. Air and substrate temperature,
solar irradiance, air humidity, water supply and wind speed are the most important parameters. Because the microclimatic observation
areas are small for lichens, the sensors also have to be small. Measurement of water availability is a special problem, as
it is subject to a very quick change in poikilohydrous thalli (Larson 1979). This chapter describes a new method for measuring water content using thallus impedance. This allows microhabitats to be
compared with each other, especially if these measurements are combined with those taken from sensors for solar irradiance,
thallus temperature and air temperature. In the field, the method is superior to gravimetric methods that have inaccuracies
caused by repeatedly removing the thalli. Thallus water content is determined by wind, irradiation, and temperature, and is
also influenced by substrate type (Ott et al. 1997). For this reason, all these parameters should be measured at the same time.
Lichen mycobionts are a large, polyphyletic and taxonomically heterogenous group comprising about 21% of all fungi (Hawksworth and Hill 1984). 98% of lichen-forming fungi are Ascomycetes, a few belong to the Basidiomycetes (Aphyllophorales and Agaricales), and the rest are Deuteromycetes. Only those mycobiont-photobiont associations are considered as lichens in which the fungal partner is the exhabitant in the sense of Law and Lewis (1983). Mutualistic symbioses in which fungi are inhabitants of multicellular algae are traditionally not regarded as lichens (Hawksworth 1988). Of the 46 orders of Ascomycetes accepted by Eriksson and Hawksworth (1986) 10 comprise and 6 consist entirely of lichen-forming taxa. Phycobionts of 20 chlorophycean genera (5 orders) and cyanobionts of 12 cyanobacterial genera (4 orders) have been reported as lichen photobionts. However, in an immense number of lichens the photo-biont has never been identified, not even on a generic level.
Lichen-forming fungi are, like plant pathogens or mycorrhizal fungi, a taxonomically heterogeneous, polyphyletic group of nutritional specialists which acquire fixed carbon from a living photoautotrophic partner (Tab. 1; for molecular systematics see [12]). In the lichen symbiosis the photobiont is not a multicellular structure as in fungal symbioses with plants, but a population of minute green algal and/or cyanobacterial cells. These are housed and maintained within the thallus of the mycobiont which, in most cases, is the quantitatively predominant exhabitant. According to Article 13.Id of the International Code of Botanical Nomenclature [16] the species names of lichens refer to the fungal partner. However, the taxonomic description of lichen-forming fungi is based on sexual reproductive structures which are exclusively formed in the symbiotic state, and on characteristics of the symbiotic phenotype (morphotype, chemotype etc.), i.e. the form in which we find and collect lichens in nature. Axenically cultured, aposymbiotic phenotypes differ very significantly from symbiotic ones. Therefore it is customary among lichenologists to refer to the mycobiont of a particular lichen species even when the aposymbiotic, cultured phenotype is considered.
The polyphyletic, taxonomically very heterogenous group of lichen-forming fungi comprises about 21% of all fungi (±13 250 spp. or 46% of all ascomycetes, ±50spp./0.3% of basidiomycetes, and ±200spp./1.2% of imperfect fungi [20]). Lichen-forming fungi are nutritionally specialized, but otherwise normal representatives of their subclasses, and there are no reasons for separating them taxonomically from nonlichenized taxa. In only about 2% of lichens has the photobiont ever been determined at the species level [52], and very little is known about the range of compatible photobionts of individual lichen mycobionts. A large number of lichen-forming fungi seem to be moderately specific (several algal species of a genus are acceptable partners), but highly selective towards their photobionts (compatible photobionts are often very rare in natural ecosystems, and the most common taxa of free-living algae are not acceptable partners [16]). Unicellular and filamentous Charophyceae, Chlorophyceae and Ulvophyceae [34, 48] and/or nitrogen-fixing cyanobacteria (altogether about 100 spp.) have been identified as lichen photobionts [52]. The lichen symbiosis is not inheritable, but numerous taxa disperse very efficiently by means of vegetative symbiotic propagules.
Fragments of several lichens were grown in the laboratory and developmental steps of growth and regeneration could be described. Different degrees of determination could be observed. The stages of podetial development inCladonia are easily distinguished and are reached after comparably short time. As they occur highly synchronized the results encourage further morphogenetic experiments.
Spribille, T., Schultz, M., breuSS, O. & bergmeier,�E. 2006. Notes on the lichens and lichenicolous fungi of western Crete (Greece). - Herzogia 19: 125-148. We report a total of 248 species of lichens and lichenicolous fungi from recent floristic work in western Crete. A total of 103 taxa are reported from the island for the first time; at least 16 taxa are new to Greece. Two species, Peccania teretiuscula and Verrucaria werneri, are new to Europe and both are reported for only the second time since their de- scription. Lichens that disperse by asexual reproductive structures (soredia, isidia) constitute only a small proportion of the flora and most species with this dispersal strategy are relatively infrequent. Some possible reasons for this as well as general patterns in the epiphytic lichen flora are discussed. Zusammenfassung: Spribille, T., Schultz, M., breuSS, O. & bergmeier,� E. 2006. Beitrag zur Kenntnis der Flechten und lichenicolen Pilze West-Kretas (Griechenland). - Herzogia 19: 125-148. In diesem Beitrag berichten wir über Nachweise von 248 Arten von Flechten und lichenicolen Pilzen von West-Kreta. 103 Taxa sind Erstnachweise für Kreta, davon werden auch mindestens 16 erstmals für Griechenland angegeben. Peccania teretiuscula und Verrucaria werneri sind neu für Europa und waren bisher nur von der Typuslokalität be- kannt. Flechten, die sich mittels asexueller Reproduktionseinheiten (Soredien, Isidien) ausbreiten, machen nur einen kleinen Teil der Flechtenflora Kretas aus, und die meisten dieser Arten sind recht selten. Mögliche Gründe dafür sowie allgemeine Muster der epiphytischen Flechtenflora werden diskutiert.
Abstract: Quantitative relationships between thallus structure
and water storage and retention capacities in 12 species of the
lichen family Umbilicariaceae were explored using three recent
techniques for plant structure analysis: stereology (3D quantification
of microscopic images), mercury intrusion porosimetry
(determination of pore size distribution of tissues) and lowtemperature
scanning electron microscopy (LTSEM). Water storage
capacity of the thallus was related neither to thallus density
nor surface area of the thallus; it was directly related to the
total porosity of the thallus and inversely related to the proportion
of thallus volume occupied by cell walls and gelatinous
substances. Water retention capacity increased with increasing
thallus density and was decreased by slight increases in the surface
area of the upper side of the thallus. Water storage and retention
capacities exhibited a positive correlation only when
the storage capacity was expressed on a surface area basis.
LTSEM study of fully hydrated specimens revealed that many intercellular
spaces of the upper cortex and upper parts of the algal
layer contained liquid water. Intercellular spaces of the lower
part of the algal layer and medulla were in general either airfilled
or partially occupied by gelatinous substances. Species
with rhizinomorphs and substrate-hygrophytic (water uptake
from surface run-offs) stored more water and retained it longer
than aerohygrophytic species (water uptake from the atmosphere)
lacking rhlzlnornorphs. Thallus structure of aerohygrophytic
species seems to facilitate rapid gas exchange with the
environment, improving water uptake and carbon gain when
atmospheric moisture is available but accelerating dehydration
when the atmosphere becomes dry.
Key words: lichen, water storage, stereology, low temperature
scanning electron microscopy (LTSEM), functional structure,
mercury intrusion porosimetry, Umbilicariaceae.
Introduction
Anzia electra sp. nov. is described and illustrated from Baltic amber dating back approx. 40 Myr. The diagnostic features of the fossilised species include the small, narrow lobed foliose thallus, two-layered medulla, lack of chondroidal axis, moniliform spongiostratum, and rhizines born singly at the margins of spongiostratum cushions. The fossil species demonstrates that all distinguishing features in the thallus morphology of Anzia sect. Anzia have remained stable for tens of millions of years. Hence the divergence of anzioid lichens must have occurred in the distant past, most probably before the Tertiary. The fossil also provides the ®rst hard evidence that the disjunct-Laurasian distributions of some modern lichens represent relicts of a formerly wider range. The close similarity of the fossil to extant species in East Asia and eastern North America suggests that the present range of Anzia sect. Anzia is highly relict.
Lichens are poikilohydric organisms that have access to a variety of different water resources such as rain, fog, dew and water vapour to conduct photosynthesis. Lichens directly interact with their adjacent environment within an equilibrium between desiccation and rewetting, nutrient uptake and release, as well as photosynthesis and respiration. They do not feature active control mechanisms such as stomata to reduce the transpiration and to take up CO2 nor roots or vascular systems for permanent water supply. Instead, they passively exchange re-sources over their entire surface. During metabolic activity, they accumulate substances taken up from the environment in their organic material. This applies not only for polluting sub-stances such as SO2, heavy metals or excess of nitrogen, but also for CO2 and water resources. Our investigations highlighted that, particularly with regard to the utilisation of water re-sources, lichens follow an alternative strategy in comparison to vascular plants. Within the scope of current investigations on how to counteract climate change, it is important to under-stand the complex water and gas exchange mechanisms. However, the characterisation of both micro- and macrohabitats as well as long-term changes requires an excessive application of apparative and economic investment. Moreover, passive gas and water exchange processes, as exhibited by cryptogams, are not yet considered in current flux models.
Recent studies indicate the suitability of naturally occurring compositions of stable isotopes (13C and 18O) of epiphytic lichens to be used as indicators for a qualitative evaluation of CO2 and water exchange processes. On the basis of our novel model the mechanisms of passive water exchange processes of cryptogams can be studied in more detail. Thus, with the knowl-edge of the respective isotopic fractionation processes, the isotope signature of lichens can be used to gain new insights into CO2 and water circulations which, prospectively, may be incor-porated in existing flux models.
Juvenile development from sown vegetative diaspores of the cyanobacterial lichen Lobaria scrobiculata and the green algal lichens Platismatia glauca and P. norvegica was studied through a four-year field experiment in a boreal spruce forest. All three species developed juvenile thalli within the period of observation. The largest lobules of L. scrobiculata and Platismatia were 0.4 mm and 1.3 mm, respectively, four years after sowing the diaspores. The first very tiny lobule (0.1 mm) of L. scrobiculata was observed 29 months after sowing the soredia. This period of juvenile development is the longest period so far reported for lichens. A long phase of dormancy, after the diaspores were attached to the substrate, was characteristic for the investigated species. Apical growth of the isidia of Platismatia glauca and P. norvegica was not observed until 21 months after sowing. Low light levels, low temperatures and snow covering the diaspores during winter, causes a short growth season in boreal spruce forests. These factors might explain the long period for juvenile development. The results indicate a slow rate of colonization of a new habitat for the investigated species since they need several years to grow to visible thalli.
Cryotechniques, such as low temperature scanning electron microscopy (LTSEM) and freeze-substitution for transmission electron microscopy (TEM), were applied to two cyanobacterial and three green algal macrolichens in order to locate free water and to visualize drought-induced structural alterations at the mycobiont—photobiont interface. The following species were examined:Peltigera canina/Nostoc punctiforme, Sticta sylvatica/Nostoc sp. (both Peltigerales),Parmelia sulcata/Trebouxia impressa, Hypogymnia physodes/Trebouxia sp. (both Lecanorales), andXanthoria parietina/Trebouxia arboricola (Teloschistales). In all species free water was confined to the symplast and the apoplast. No intercellular water reservoirs were found in the gas-filled thallus interior. Thalline fluctuations in water content reflect fluctuations in apoplastic and symplastic water. All the taxonomically diverse lichen photobionts have access to water and dissolved nutrients via the fungal apoplast only. Drought stress (i.e., water content 20%/dw and below) caused dramatic shrinkage and deformation in all cell types. At any level of hydration the fungal and algal protoplast maintained close contact with the cell wall. This applied to the cyanobacterial photobionts and their murein sacculus and gelatinous sheath too. Although the cytoplasm of both partners was strongly condensed in desiccated lichens the cellular membrane systems, usually negatively contrasted, were very well preserved. The significance of these data is discussed with regard to the functioning of the symbiotic relationship.
Structural alterations of the photobiont and mycobiont cells of lichens have been related to CO2-gas exchange during experiments involving water vapour uptake and desiccation of liquid-water-saturated thalli. Increasing water vapour uptake of air dry lichens led to a gradual unfolding of the photobiont cells in Lobaria pulmonaria, Pseudevernia furfuracea, Ramalina maciformis and Teloschistes lacunosus as studied by low-temperature scanning electron microscopy. The data indicated that globular, probably turgid, cells and also slightly infolded or even heavily collapsed cells contributed to positive net photosynthesis, which was reached after water vapour uptake by the four species studied. During desiccation of fully water-saturated thalli of L. pulmonaria, extrathalline water films gradually evaporated before maximum values of CO2-gas exchange were measured and before photobiont cells started to shrivel. In contrast, in P. furfuracea the CO2-gas exchange maximum was reached when a considerable percentage of photobiont cells had already collapsed and while other parts of the thalli were still covered with liquid water. Further desiccation led to cavitation of the cortical cells in both species, this occurring at water contents at which net photosynthesis was still positive.
Understanding the factors limiting the distribution of a species is crucial for designing conservation strategies. We evaluated whether the scarcity of old-forest lichens in young forests was due to unfavourable environmental conditions for colonization in young stands or to dispersal limitations. Vegetative diaspores of Lobaria scrobiculata, Platismatia glauca and Platismatia norvegica were sown on 240 spruce twigs transplanted to a young and an old stand of spruce. Our results demonstrate that the old-forest species established and grew as rapidly in the young as in the old forest. Higher light levels in the young, compared with the old forest, did not reduce diaspore development. Moreover, greater numbers of juvenile thalli of Platismatia were found on control twigs (unsown) in the old forest, compared with the young forest, suggesting higher propagule density and more efficient dispersal in the old stand. Our results indicate that life-history characteristics, which include dispersal characters, are important for explaining the species scarcity in younger stands. Minimizing the distance between regeneration units and potential sources of propagules is probably important for maintaining lichen biodiversity in managed forest ecosystems.
The intrathalline heterogeneity of chlorophyll a fluorescence (CaF) in thalli of the foliose lichen Flavoparmelia caperata was studied measuring Fo, Fm, Fv/Fm, ΔF/Fm′, NPQ and Ft in two spots of 25 mm2 positioned at ca 0.8 and 3 cm from the thallus margin. Measurements were carried out both in the field and in the laboratory using north-exposed, epiphytic thalli occurring in a deciduous wood of the Karst plateau (Trieste, NE Italy). With the exception of NPQ, all parameters were statistically higher in the marginal spots than in the central ones, suggesting that the level of photochemical activity is higher where the photobiont cells are more dense and younger. Fm and Fv/Fm of marginal spots measured in the field were statistically lower than those measured in the laboratory, probably as a consequence of the different pre-treatment conditions. The importance of selecting a specific measuring spot, particularly for biomonitoring purposes, is discussed.
Flere institusjoner har søkt å skaffe oversikt over den ujevne belastning ulike fjellavsnitt har fått i Skandinavia, særlig med tanke på forholdene for vill og tam rein. Våre resultater viser at en trenger store prøveserier av lav fra hvert fjellområde for å kunne foreta slike sammenligninger. På den annen side er det gode muligheter for å begrense samleprogrammet ved stratifiering etter høgde og eksponering.
The hypothesis that CO(2) gas exchange and chlorophyll a fluorescence (ChlaF) of lichens vary according to the light regimes of their original habitat, as observed in vascular plants, was tested by analysing the photosynthetic performance of 12 populations of seven dorsoventral, foliose lichens collected from open, south-exposed rocks to densely shaded forests. Light response curves were induced at optimum thallus water content and ChlaF emission curves at the species-specific photon flux at which the quantum yield of CO(2) assimilation is the highest and is saturating the photosynthetic process. Photosynthetic pigments were quantified in crude extracts. The results confirm that the maximum rate of gross photosynthesis is correlated with the chlorophyll content of lichens, which is influenced by light as well as by nitrogen availability. Like leaves, shade tolerant lichens emit more ChlaF than sun-loving ones, whereas the photosynthetic quantum conversion is higher in the latter.
The stable isotopic composition of water is routinely used as a tracer to study water exchange processes in vascular plants and ecosystems. To date, no study has focussed on isotope processes in non-vascular, poikilohydric organisms such as lichens and bryophytes. To understand basic isotope exchange processes of non-vascular plants, thallus water isotopic composition was studied in various green-algal lichens exposed to desiccation. The study indicates that lichens equilibrate with the isotopic composition of surrounding water vapour. A model was developed as a proof of concept that accounts for the specific water relations of these poikilohydric organisms. The approach incorporates first their variable thallus water potential and second a compartmentation of the thallus water into two isotopically distinct but connected water pools. Moreover, the results represent first steps towards the development of poikilohydric organisms as a recorder of ambient vapour isotopic composition.
Kaiserslautern, Universiẗat, Diss., 2002 (Nicht für den Austausch).
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