Structural Aspects of the Lichen-Rock Interface Using Back-scattered Electron Imaging

The profound knowledge of the structural and chemical characteristics of the interface between lichen thallus and rock, seems to be indispensable for the process of understanding the lichen symbiosis as well as the significance of the weathering action of lichens. One of the most promising techniques to be used in this investigation is the Scanning Electron Microscopy (SEM) in the back-scattered electron (BSE) emission mode. In the present work thalli of Parmelia conspersa, Aspicilia intermutans and Lecidea auriculata growing in granitic rock were examined by SEM in BSE mode with (Energy Dispersive Spectroscopy) EDS. In the case of the foliose thalli the observation of the interface permits detection of the rhizine/hyphae adherence and determination of the origin of the minerals which adhere to the rhizine/hyphae. In the case of the crustose thalli BSE permits investigation within the ultrastructure of the crustose thallus and crustose lichen-rock contact zone and also allows observations of the penetration and filling of the fissures and cracks of the underlying rock by components of the thallus and other living organisms. The BSE images could contribute to a better knowledge of the cytological state of the rock-inhabiting organisms and also to the understanding of the action of the chemical treatments used in the removal of lichen from building materials.     

The delimitation of Psora (Lecideaceae) and related genera, with notes on some species

A new delimitation of the lichen genus Psora Hoffm. is proposed. The genus is mainly characterized by a squamulose thallus, an upper cortex of 'Scheinrindentyp', a hypothecium containing calcium oxalate, an amyloid hymenium containing anthra–quinones, the type of ascus and the type of pycnidium. The affinities of Psora to the genera Eremastrella, Psorula , and Xanthopsora and some squamulose species provisionally included in Lecidea are discussed. The genus Chrysopsora is reduced to syn–onomy with Psora , and the species Lecidea hedinii, L. scholanderi , and Psora petri to synonomy with Lecidea pulcherrima, Toninia tristis , and Lecidea lurida , respectively. The new combinations Lecanora scotopholis (Tuck.) Timdal, Psora hypotheja (Lamb) Timdal, P. subrubiformis (Vainio) Timdal, and P. vallesiaca (Schaerer) Timdal are proposed.
New chemical data are given for a number of the species and chemical strains are recognized for the first time in Psora crenala, P. globifera, P. gresinonis , and P. rubifor–mis. Two new chemical strains of P. decipiens are recorded.     

Cephalodiate Arten der GattungLecidea sensu lato (Ascomycetes lichenisati)

(1) The ability to produce cephalodia is usually a genus-specific character in lichens. (2)Lecidea shushanii Thoms., is a member of the genusTephromela, closely related toT. aglaea. It is not clear, whether or not the cephalodia of this taxon are true cephalodia or colonies of epiphytic cyanobacteria and whether or notLecidea shushanii is an independent species. (3)Lecidea dovrensis Nyl., is, in contrast to the traditional concept, not conspecific withLecidea alpestris Sommerf., but an earlier name forLecidea pallida Th. Fr. (4)Lecidea dovrensis is described in some detail. Chemically the species is characterized by the presence of isousnic acid (previously unknown in lecideoid lichens). It is restricted to areas north of the 60th parallel with an oceanic climate. (5) In connection with the attempt to clarify the taxonomic relationships ofLecidea dovrensis, figures of ascus apical structures of the following species are given (marked by an asterisk are genera where we found discrepancies with published data):Austrolecia antarctica, Catillaria chalybeia, Lecidea alpestris, L. caesioatra, L. limosa, Lecidoma demissum, Koerberiella wimmeriana, Micarea assimilata, M. crassipes, M. melaenida, M. prasina, Pilophorus robustus, Placodiella olivacea, Placolecis opaca, Porpidia trullisata, Protoblastenia rupestris, Psilolechia lucida, Psorula rufonigra, Squamarina gypsacea, Xanthopsorella texana. (6) Among crustaceous lichens we find no groups related toLecidea dovrensis. We supportTimal's concept of including this species in the genusPilophorus. Pilophorus, as well asLecidea dovrensis is characterized by the same ascus type, by a similar structure of thallus, cephalodia, paraphyses, and ascocarp (although there is no pseudopodetium developed inLecidea dovrensis), and the presence of isousnic acid. In addition, both taxa are restricted to cool oceanic climates and non-calciferous substrates. The following combination is proposed:Pilophorus dovrensis (Nyl.)Timdal, Hertel & Rambold, comb. nova. (7) The species of theLecidea alpestris-group form an independent genus, probably near toAustrolecia Hertel.

Frau Prof. Dr.Elisabeth Tschermak-Woess zu ihrem 70. Geburtstag gewidmet.     

Pseudoperichaeta insidiosa un nouveau tachinaire[DIP.] élevé dansGalleria mellonella [Lep.]

Résumé Pseudoperichaeta insidiosa R.D., tachinaire parasite non spécifique d'Ostrinia nubilalis Hübner est élevée pour la première fois dans les larves deGalleria mellonella L. La méthode d'élevage est exposée en détail et certaines caractéristiques biologiques du développement post-embryonnaire sur cet h?te de substitution sont définies. Quelques éléments de la biologie des adultes au laboratoire sont décrits.

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Summary For the first time,Pseudoperichaeta insidiosa R.D., a non specific tachinid parasite ofOstrinia nubilalis (Hübner), was reared onGalleria mellonella L. With this substitution host a yield of about 0.35 pupa per deposited planidium is obtained. The mean pupal weight is 28.8 mg with 1 planidium per host and 25.0 with 2. Some post embryonic development and adult biological features are given. The whole life cycle lasts about 45 days. Till now 8 generations have been reared.

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Avec la collaboration technique deColette Ogier.     

The weathering action of saxicolous lichens in maritime Antarctica

Summary Xanthoria elegans (Link) Th Fr. and Lecidea lapicida (Ach.) were studied on volcanic andesite, and Rhizocarpon geographicum (L.) DC. and Bacidia stipata Lamb on a volcanigenic sediment, using light microscopy, infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Feldspars were present in the rocklichen interface to a lesser extent than in the underlying rock. R. geographicum was found to alter the minerals in the rock on which it grew without producing any new minerals in the rock/lichen interface, in contrast to the observations for this species on granite in temperate regions. Beneath of the thallus of L. lapicida there was calcium oxalate and some micas of the illite type, which may have been degradation products of various phyllosilicates in the rock. B. stipata, an endemic Antarctic lichen, had the greatest capacity to weather the rock and had weddellite (dihydrate calcium oxalate) and calcite in the contact area as well as many bacteria. The presence of crystalline oxalate, imogolite, allophane, carbonates (calcite) and amorphous material not found in the parent rock indicates biomineralization processes attributable to the lichens.     

网衣属3个中国新记录种

该研究以采集于中国新疆地区的网衣科网衣属地衣标本为试验材料,采用形态解剖学、地衣化学物质检测方法和系统发育学方法,观察分析网衣属地衣的形态解剖特征、次生代谢产物以及核糖体DNA内转录间隔区(internal transcribed spacer,ITS)系统发育树,依据形态解剖数据、次生代谢产物种类以及系统发育树分类地位更为综合的鉴定种。结果显示：(1)共鉴定出网衣科网衣属3个中国新记录种——暗色网衣(Lecidea fuscoatrina Hertel & Leuckert)、珠光网衣(Lecidea perlatolica Hertel & Leuckert)和多器网衣(Lecidea polypycnidophora U. Rupr. & Türk),并提供了3个新记录的形态解剖图。(2)ITS系统发育树结果表明,暗色网衣与近缘种Lecidea atrobrunnea原种及亚种、Lecidea fuscoatra、珠光网衣与近缘种Lecidea promiscens以及Lecidea polypycnidophora与近缘种Lecidea andersonii各形成一个分支,依据分支组成可将形态差异不明显的近缘种鉴别开。     

CYANOPHYTE CEPHALODIA IN THE LICHEN GENUS NEPHROMA

The lichens, Nephroma expallidum (Nyl.) Nyl. and N. arcticum (L.) Torss., consistently have at least two symbionts in a single thallus: a green alga in the algal layer and a blue-green alga in the internal cephalodia. The cephalodia originate from algal cells in contact with the lower surface of the lichen, in the zone of rhizine formation. The rhizines surround the epiphytic algal colony and form a second cortical layer; following dissociation of the original lower cortex, further growth of the two organisms results in the cyanophyte colony being enveloped by a compact layer of fungal tissue and positioned in the lichen medulla. The colony may eventually assume a superior or inferior position in relation to the lichen thallus, depending in part on the lichen species. Nephroma anticum may have two distinct morphological forms of blue-green algae in the same thallus and occasionally in the same cephalodium. It appears that the relationship that exists between the cephalodial algae and the lichen thallus is antagonistic and results, in some cases, in the exclusion of the green algal layer and death to the cephalodial cyanophytes.     

Photobiont Selectivity and Interspecific Interactions in Lichen Communities. I. Culture Experiments with the Mycobiont Fulgensia bracteata

Abstract: Lichen communities are characterised by interspecific interactions that not only include interactions between different lichen species but also between the symbionts within a single lichen species. The community “Bunte Erdflechtengesellschaft”, growing on weathered calciferous rocks known as Gravel Alvar on Gotland (Baltic Sea, Sweden), shows a high complexity of inter‐ and intraspecific interactions, including Fulgensia bracteata, F. fulgens, Toninia sedifolia, Squamarina cartilaginea, Psora decipiens and Lecidea lurida. F. bracteata and F. fulgens are the dominant species of this community, showing a tendency to overgrow the other species involved and even parasitic behaviour. Culture experiments have been performed to investigate the selectivity of the mycobiont of F. bracteata towards a variety of potential photobionts. The results provide evidence for the selectivity of the mycobiont and varying compatibility of the respective symbionts that can be interpreted as a cascade of interdependent processes of specific and non‐specific reactions of the symbionts involved.     

Some ecological aspects of the copepod parasites of the common hake, merluccius hubbsi, from the argentineuruguayan coasts

A total of 2164 common hake Merluccius hubbsi captured in the Argentine-Uruguayan Common Fishing Zone was examined for parasitic copepods. The fish were infested with Chondracanlhus palpifer and Neobrachietia insidiosa f. lageniformis, the former parasitizing the buccal cavity and the latter the branchial arches. C. palpifer showed an increase in both prevalence and intensity in relation to the host size; infestation with N. insidiosa f. lageniformis decreased with increasing length of hake. Attachment site preferences and variations in the parasite distribution patterns as related to the host biology were observed. Evidence of negative association between copepod species and seasonal changes in the parasite composition was also found.     

ERUMPENT CEPHALODIA,AN APPARENT CASE OF PHYCOBIAL INFLUENCE ON LICHEN MORPHOLOGY1,2,3

On the upper surface of some specimens of the lichen Lobaria cf. crosa (Eschw.) Nyl. there are shrub-like growths which have a morphology similar to that of a free-living fruticose lichen, Polychidium umhausense (Auersw.) Henss., and contain a cyanophyte phycobiont, Nostoc. A few growths also contain scattered colonies of a chlorophyte phycobiont, in which case the lichen tissue locally assumes the foliose form characteristic of the parent Lobaria thallus. The differentiation of dorsiventral lichen cortices and the formation of a lax medulla and distinct algal layer are correlated with the presence of the green phycobiont. The lichen substances atranorin, gyrophoric acid, and 4-0-methylgyrophoric acid occur in both, the foliose L. erosa thallus and the fruticose tissue. It is suggested that the fruticose structures are erumpent cephalodia which are derived from the outgrowth of internal, cephalodia and should not be considered, to be epiphytic colonies of the lichen Polychidium.     

Lichenizing Rhizomorphs and Thallus Development in the Squamulose Lichen Aspicilia crespiana Rico ined. (Lecanorales,Ascomycetes)

This work describes the rhizomorphs and their relation to thallus development in the squamulose lichen Aspicilia crespiana Rico ined. The rhizomorphs capture algal cells, giving rise to new squamules terminally or laterally. The thallus thus consists of a network of lichenized squamules interlinked by mycobiontic rhizomorphs. A previously proposed comparison of lichen rhizomorphs to the prothallus (hypothallus) of crustose lichens is applied and expanded upon. Other less organized prothallic structures sometimes produced by A. crespiana are also described. The importance of lichenizing rhizomorphs as an essential feature of thallus growth in this species is emphasized and a competitive role in substrate occupation and thallus expansion is suggested.     

Morphology and anatomy ofCaloplaca coralligera (Teloschistaceae) as adaptation to extreme environmental conditions in the maritime Antarctic

The anatomical and morphological structure of the lichenCaloplaca coralligera (Hue.)Zahlbr. was investigated in connection with mechanisms of colonization and adaptation to the special conditions of maritime Antarctic.Caloplaca coralligera seems to be endemic to the antarctic region. The lichen is unique in its morphology, growing like a crustose lichen with a prothallus, but the very thallus being composed of many vertical, frutescent branches not higher than large isidia. Due to fusions of the distal parts of the branches the morphology is characterized by air-filled cavities between the erect thallus parts where the phycobionts are located only close to the outermost surface. But also anatomically a system of air-filled cavities is developed by a net-like structure of hyphae. This may result in an insulation from temperature exchanges with the rocky substrate. It is speculated that this peculiar thallus structure might be advantageous to a lichen growing on compact substrates by buffering the diurnal temperature extremes which are characteristic for rocks under a strong radiation exchange with the atmospheric surrounding.Dedicated to Prof. DrO. L. Lange on the occasion of his retirement and of his 65th birthday.     

Ultraviolet-absorbing scytonemin and mycosporine-like amino acid derivatives in exposed, rock-inhabiting cyanobacterial lichens

 The occurrence of ultraviolet (UV)-absorbing substances like scytonemin and mycosporine-glycine is reported for the first time from cyanobacterial lichens of the genera Collema, Gonohymenia and Peltula, all coming from high-light-intensity habitats. Except for Collema with the filamentous Nostoc, all other cyanobionts belong to the unicellular genera Chroococcidiopsis, Cyanosarcina, Gloeocapsa or Myxosarcina. From transmission electron microscope studies it is evident that the pigmentation (scytonemin) is located extracellularly in the sheath of the outer thallus parts. Fluorescence microscopy and microprobe measurements clearly show UV radiation into the lichen thallus and hence the relevance of UV sunscreens for the protection of the organism. Received: 4 March 1997 / Accepted: 20 May 1997     

POROSIMETRIC STUDY OF THE LICHEN FAMILY UMBILICARIACEAE: ANATOMICAL INTERPRETATION AND IMPLICATIONS FOR WATER STORAGE CAPACITY OF THE THALLUS

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.     

Moisture content and CO2 exchange of lichens

Summary Net photosynthesis (10 klx light intensity, 150 E m^-2 s^-1 PAR) and dark respiration of the lichen Ramalina maciformis at different temperatures are measured in relation to thallus water content. Both first increase with increasing hydration. Dark respiration then remains constant with increased water content until thallus saturation. In contrast, a further increase in water content leads to a depression of net photosynthesis, as shown in previous studies, after a maximum of CO₂ uptake has been attained. However, the extent of this depression depends strongly on temperature. In saturated thalli (160% water content in relation to lichen dry weight) the depression amounts to about 15% and 63% of the maximum unsaturated rate at 5°C and 25°C thallus temperature, respectively. The moisture compensation-point of net photosynthesis is also decisively determined by temperature (for 0°C at 20% water content; for 25°C at 15%), and the water content that allows maximum rates of CO₂ uptake (for 0°C at 80%; for 25°C at less than 40% water content). An electrical analogue of CO₂ exchange in a lichen thallus is presented, and it is suggested that the experimental results may be interpreted in terms of temperature-dependent CO₂ diffusion resistances in imbibed lichen thalli.     

Electron microscopic study of the lichenDermatocarpon hepaticum (Ach.) Th. Fr.

Summary The ultrastructure of the alga and fungus of the lichenDermatocarpon hepaticum and their relationship has been studied. The contact between the symbionts was found to be of a different type from that found in other lichen species, and to some extent comparable with the relation of obligate parasites and their host.The anatomy of the thallus and the distribution pattern of the components in the thallus has been revealed by examining serial sections.     

A Note on the Relationship Between Some Saxicolous Lichens and Manganese Ore in North Wales,UK

Manganese oxyhydroxides have been found deposited on the surface of the lichen Catillaria chalybeia on an altered rhodochrosite. It is suggested that the Mn was mobilised from the ore surface via surface-weathering and redeposited in the thallus. The lichen Acarospora smaragdula also grew upon the ore but showed no sign of Mn deposition. Nine further lichens and two bryophytes were also found on the ore.     

Differenze Ultrastrutturali Di Alcune Specie Di Trebouxia Poste in Condizioni Di Illuminazione Differenti

Abstract

Ultrastructural changes in some species of « Trebouxia » under different light conditions. — Some species of the phycobiont alga Trebouxia (Tr. decolorans and Tr. albulescens), both isolated and grown on synthetic medium and still in the lichen, were examined in order to study the effect of light on the plastid ultrastructures. The species isolated from Buellia punctata and Xanthoria parietina were very sensitive to light condition and lost their chlorophyll content quickly. Striking ultrastructural changes were found in the algae grown under small light intensities and those which become achloric owing to strong light. In the latter, modifications of the Iamellar System were observed. The disappearance of Chlorophyll pigments was followed by a reduced electron density of the whole Iamellar system, as if were lacking the Iipidic compounds which are usually present and absorb fixators and dyers, thus allowing a good view. On the contrary, normal light conditions did not affect cultures of Trebouxia humicola, a free living alga. In the chloroplasts of the phycobiont species, unlike in the free living alga, grana were very close and sometimes formed very thick masses towards the edge of the chloroplast. It could not be ascertained whether such changes corresponded to a different composition of the lipoproteic compounds of the lamellar system.

Xanthoria parietina could grow in very lighted environments with no damage of the algae present in its thallus. The lichen thalluses, under different light conditions, showed very different colourings: the overlighted ones were rusty-red and the shadowed ones deep green. The chlorophyll content of the lichen thalluses with various shades (table 1) were very similar. The ultrastructural changes induced by strong light intensities in the phycobiont algae, kept in the lichen, were very small in respect of those observed in the same algae isolated and grown on synthetic medium and concerned the Iamellar system and the pyrenoid, above all. The rusty-red lichen showed a great number of stromatic lamellae, often with a parallel trend, so as to simulate a Iamellar system not organized in grana and often presented groups of lamellae concentrically arranged. In the pyrenoid of the algae from rusty-red thalluses, compared with the green ones, a much greater number of electron dense masses was observed, which are very thick and occupy the whole stromatic portion of the pyrenoid. But the Chlorophyll content did not decrease. Unlike the results of PEVELING, we noted that the electron dense masses (cited by the Author as « osmiophilic plastoglobules) were visible even after fixation with permanganate; the different numbers of these globules might depend on environmental factors. The phycobiont alga, when in the lichen thallus, could perhaps support strong light intensities, because pigments or compounds formed with the mycobiont or by it alone prevented the photooxidation of chlorophyll. Hypothetically a relationship might exist between the sensitivity of the phycobiont algae to light intensities and the content in antraquinonic pigments in the lichen thallus. But also using filters with absorption maxima similar to those of these pigments, the « in vitro » cultures of the phycobiont algae became achloric in the same time as the control ones.

Some Authors had found in Trebouxia humicola a different relationship between Chlorophyll pigments and carotinoids from that observed in the phycobiont species and had ascribed to it the greater resistence to strong light of the free living alga. Pigments or other substances present in the mycobiont can have a protective action on the Chlorophyll content and on the ultrastructures. In the phycobiont algae the resistence to strong light might be explained by an exchange of compounds between mycobiont and phycobiont, ending with the structural changes of the pyrenoid.     

Spatial organization of the three‐component lichen Peltigera aphthosa in functional terms

The cephalolichen Peltigera aphthosa (L.) Willd. is characterized by lateral heterogeneity, which manifests itself in the presence of three thallus zones, referred to as the apical, basal and medial zone. These zones differ in terms of interaction between lichen bionts and their physiological activity. The apical thallus zone is more efficient in establishing a contact with cyanobacteria, because of a higher lectin content and a larger overall thallus surface area due to the presence of numerous mycobiont hyphae. Cephalodia are formed in this zone. The interaction between the mycobiont and cyanobiont is more intense in the medial zone. However, the establishment of the contact with cyanobacteria in this zone less probable. The spatial distribution of lectins in the thallus was determined. To reveal the differences in photosynthetic activity in three thallus zones, transient analysis of chlorophyll a fluorescence and the assessment of non‐photochemical quenching of excited chlorophyll states were performed. Assimilation of absorbed light energy was more effective in the medial zone. The basal zone was characterized by decreased photosynthetic activity, lichen dissociation and thallus death.