Lichen-rock Interface Research Articles

Variation of heavy metals, magnetic susceptibility, and some chemical properties in the Lichen-rock interface on various parent rocks in west of Iran

This investigation was directed to explore the impacts of Lecanora Ach. (1809) on magnetic susceptibility, some chemical properties, and heavy metals concentration in the interfaces with interior rocks including andesite, diorite, tuff, and hornblende-gabbro in the west of Iran. In each of the selected rocks, 15 samples of lichen-rock interfaces were excoriated and analyzed for heavy metals, some chemical analyses, and magnetic susceptibility (χ). The results showed that most of metals were reduced significantly (p < 0.05) in lichen-rock interfaces as compared to interior rocks, that mainly related to weathering and leaching of metals from the rocks and consequently related to dilution effects that cause reduction of the concentration of metals in the mass unit. Comparison of magnetic susceptibility in the lichen-rock interface with interior rocks showed that there is a significant reduction of χlf (magnetic susceptibility at low frequency) for developed soils on the rocks compared to interior rocks in all cases. This may be related to dilution of ferrimagnetic minerals in the interface by the presence of paramagnetic minerals (phyllosilicates) or diamagnetic (calcium carbonates and organic materials) in the interfaces. Lichen is grown on the various rocks showed significant differences for pH, calcium carbonate equivalent (CCE), and Fed (iron extracted by dithionite), which mainly attributed to the nature of parent rocks. The results of multiple linear regression (MLR) indicated that soil properties included total Fe, Fed, OM (organic matter) and CCE explained about 79% of the variability in χlf in lichen-rock interfaces. For further clarification of complicated processes that occurred in the interfaces between lichen and rocks regarding soil pedogenesis as well as an indicator of bio-monitoring, further investigations on the various rocks and different species of lichen are recommended.

Lichens and other lithobionts on the carbonate rock surfaces of the heritage site of the tomb of Lazarus (Palestinian territories): diversity, biodeterioration, and control issues in a semi-arid environment

Investigations on the lithobiontic colonization of the stone cultural heritage in (semi-)arid regions are needed to address conservation strategies. In this work, lithobiontic communities were examined on the carbonate rock surfaces of the heritage site of the Tomb of Lazarus. We aimed to evaluate their distribution and interaction with the lithic substrate, together with the efficacy of biocidal treatments for their control. Diversity and abundance of lithobionts were surveyed on the Jerusalem stone blocks of three architectural elements. Observations at the lichen-rock interface were carried out by reflected light and scanning electron microscopy. The efficacy against lichens of the widely used biocide benzalkonium chloride (BZC) was compared for different concentrations and application methods, and evaluated by epifluorescence microscopy. Chlorolichens were the dominant component of lithobiontic communities, more thoroughly adapted to the semi-arid conditions of the site than mosses and black biofilms of cyanobacteria and dematiaceous fungi. A different structural organization, in terms of thallus thickness and depth of the hyphal penetration component, characterized epilithic and endolithic lichen species, responsible for different deteriogenic activities. Biocidal assays showed that even the methodologies that are usually effective in temperate conditions (as the application of BZC 1.5% by poultice) may not completely devitalize lichens adapted to the stress conditions of semi-arid climates, unless a pervasive biocide diffusion through metabolically active thalli is carefully guaranteed. Lithobionts act as biodeteriogens on the semi-arid surfaces of the investigated heritage site. Their removal is thus recommendable, but it needs to be adequately supported with a careful calibration of devitalization strategies.

The influence of structural organization of epilithic and endolithic lichens on limestone weathering

AbstractHyphal penetration, mineral dissolution and neoformation at the lichen–rock interface have been widely characterized by microscopic and spectroscopic studies, and considered as proxies of lichen deterioration of stone substrates. However, these phenomena have not been clearly related to experimental data on physical properties related to stone durability, and the physical consequences of lichen removal from stone surfaces have also been overlooked. In this study, we combine microscopic and spectroscopic characterization of the structural organization of epi‐ and endolithic lichens (Caloplaca marina (Wedd.) Du Rietz, Caloplaca ochracea (Schaer.) Flagey, Bagliettoa baldensis (A.Massal.) Vězda, Porina linearis (Leight.) Zahlbr., Verrucaria nigrescens Pers.) at the interface with limestones of interest for Cultural Heritage (Portland Limestone, Botticino Limestone), with analysis of rock properties (water absorption, surface hardness) relevant for durability, before and after the removal or scraping of lichen thalli. Observations using reflected‐light and electron microscopy, and Raman analyses, showed lichen–limestone stratified interfaces, differing in the presence/absence and depth of lichen anatomical layers (lithocortex, photobiont layer, pervasive and sparse hyphal penetration component) depending on species and lithology. Specific structural organizations of lichen–rock interface were found to be associated with differential patterns of water absorption increase, evaluated by Karsten tube, in comparison with surfaces with microbial biofilms only, even more pronounced after the removal or scraping of the upper structural layers. Equotip measurements on surfaces bearing intact thalli showed lower hardness in comparison with control surfaces. By contrast, after the removal or scraping procedures, Equotip values were similar to or higher than those of controls, suggesting that the increasing open porosity may be related to a biogenic hardening process. Such counterposed patterns of porosity increase and hardening need to be considered when models relating lichen occurrence on limestones and biogeomorphological surface evolution are proposed, and to evaluate the consequences of lichen removal from stone‐built cultural heritage. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Lichen colonization and associated deterioration processes in Pasargadae, UNESCO world heritage site, Iran

Knowledge on lichen and microbial colonization as well as associated biodeterioration processes of the stone cultural heritage is needed to establish proper conservation programs, but is still poor for stonework in semi-arid regions. In this study, lichen diversity was characterized on seven monumental buildings of the Pasargadae UNESCO-world heritage site (Iran). The risk of biodeterioration processes associated to lichen occurrence on two types of limestones, and the lichen resilience to mechanical cleaning intervention were examined. Physico-chemical substrate features and climatic conditions, combined with the agricultural surrounding and tourist disturbance, supported a pervasive colonization by species-poor epi- and endolithic communities, and fast recolonization processes by nitrophytic species after mechanical removal. The endolithic growth of some lichens and the penetration of hyphal structures of epilithic ones, examined by light and electron microscopy, were associated to stone disintegration and dissolution at the lichen-rock interface. Endolithic cyanobacteria were detected under lichen thalli, likely contributing to deterioration processes. Colonization and deterioration patterns did not appear peculiar with respect to previous investigations on similar communities in different climatic regions, and were mostly related to the different examined lithologies, indicating lichens as harmful biodeteriogens of the sedimentary rock materials used in the stone cultural heritage of semi-arid regions.

On the dual nature of lichen-induced rock surface weathering in contrasting micro-environments.

Contradictory evidence from biogeomorphological studies has increased the debate on the extent of lichen contribution to differential rock surface weathering in both natural and cultural settings. This study, undertaken in Côa Valley Archaeological Park, aimed at evaluating the effect of rock surface orientation on the weathering ability of dominant lichens. Hyphal penetration and oxalate formation at the lichen-rock interface were evaluated as proxies of physical and chemical weathering, respectively. A new protocol of pixel-based supervised image classification for the analysis of periodic acid-Schiff stained cross-sections of colonized schist revealed that hyphal spread of individual species was not influenced by surface orientation. However, hyphal spread was significantly higher in species dominant on northwest facing surfaces. An apparently opposite effect was noticed in terms of calcium oxalate accumulation at the lichen-rock interface; it was detected by Raman spectroscopy and complementary X-ray microdiffraction on southeast facing surfaces only. These results suggest that lichen-induced physical weathering may be most severe on northwest facing surfaces by means of an indirect effect of surface orientation on species abundance, and thus dependent on the species, whereas lichen-induced chemical weathering is apparently higher on southeast facing surfaces and dependent on micro-environmental conditions, giving only weak support to the hypothesis that lichens are responsible for the currently observed pattern of rock-art distribution in Côa Valley. Assumptions about the drivers of open-air rock-art distribution patterns elsewhere should also consider the micro-environmental controls of lichen-induced weathering, to avoid biased measures of lichen contribution to rock-art deterioration.

The Geochemical Behavior of Rare Earth Elements during the Rock Weathering and Soil Formation at Lichen-Rock Interface in Shir-kuh Granitoid Batholith of Yazd Province

The Geochemical Behavior of Rare Earth Elements during the Rock Weathering and Soil Formation at Lichen-Rock Interface in Shir-kuh Granitoid Batholith of Yazd Province

Lichen-induced biomodification of calcareous surfaces: Bioprotection versus biodeterioration

Studies demonstrate the active and passive capability of lichens to inhibit or retard the weathering of calcareous surfaces. Lichen coverage may actively protect a surface through shielding by the thallus and the binding and waterproofing of the rock surface and subsurface by fungal hyphae. Passive protection of rock surfaces may be induced by the formation of an insoluble encrustation, such as calcium oxalate, at the lichen-rock interface. Recent research suggests that the decay of hyphae, induced by changes in microenvironmental conditions, necrosis, parasitism or the natural physiological traits of particular lichen species, may expose a chemically and physically weakened substrate to dissolution, triggering relatively rapid weathering-related surface lowering. Consequently, certain epilithic crustose and endolithic lichens may induce a period of surface stability throughout the course of their lifespan, followed by a phase of instability and rapid episodic microtopographical evolution after death and decay. A series of conceptual models is proposed to illustrate this idea over short (single lichen lifespan) and long (multiple lichen lifespans) timescales. The models suggest that the microscale biogeomorphological system of lichen-rock interaction is underpinned by non-linear dynamical system theory as it exhibits dynamical instability and is consequently difficult to predict over a long timescale. Dominance by biodeterioration or bioprotection may be altered by changes in lichen species or in environmental conditions over time.

Role of lichens in weathering of granodiorite in the Sila uplands (Calabria, southern Italy)

This paper explores the role of five recurrent epilithic lichen species (Aspicilia intermutans (Nyl.) Arnold, Xanthoparmelia pulla (Ach.) O. Blanco, A. Crespo, Elix, D. Hawksw. & Lumbsch, Rhizocarpon lecanorinum Anders, Tephromela atra (Huds.) Hafellner and Lecanora bolcana (Pollini) Poelt), which encrust granodiorite spheroidal boulders exposed in the Sila uplands (Calabria, southern Italy), in weathering of plutonic rocks in a typical mountainous Mediterranean environment. A detailed investigation was carried out on the lichen–rock interface of each species, by comparing them mutually and with lichen-free granodiorite samples. For this purpose, the lichen species were sampled together with the encrusted rock surface for detailed mineral-petrographic analyses performed in thin and ultra-thin sections. Optical and scanning electron microscopy of these sections and of bulk samples permitted us to highlight the peculiar modes of physical and chemical attacks of lichen thalli and hyphae on and into the substratum for each species. Crack systems often parallel to the outer rock surface appear often intruded by hyphae, which cause rupture of primary minerals, with detachment and progressive incorporation of their fragments into the thallus. In particular, the species L. bolcana and T. atra revealed an unexpected, partly endolithic behavior, presumably enhanced by the presence of rock fractures earlier generated by other physical breakage processes already affecting the spheroidal boulders in the Sila mountains. Dissolution features often affect primary minerals (even quartz), that may show very peculiar patterns which are suggestive of a biologically-induced control. Various phyllosilicate clay minerals were identified using SEM–EDS microprobe analyses and FT-IR spectroscopy, which also enabled the identification of possible amorphous silica (or quartz micrograins), rhizocarpic acid and carotenoid at the encrusted granodiorite interface. In contrast, neither oxalic acids nor oxalates were detected.

Microscale biopitting by the endolithic lichen Verrucaria baldensis and its proposed role in mesoscale solution basin development on limestone

Data are reported demonstrating the potential role of microscale morphologies, induced by endolithic lichen communities, specifically Verrucaria baldensis, in the initiation and development of mesoscale solution basin formation on limestone in the Burren, County Clare. A biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth, associated perithecial biopitting followed by biopit coalescence to form biotroughs, their subsequent enlargement and eventual incipient solution basin formation. This model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input. The complexity of interactions at the lichen–rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that, as with macrotopographies at the landscape scale, rock surface microtopographies also reflect historical weathering legacies. Copyright © 2011 John Wiley & Sons, Ltd.

Pedogenetic action of the lichens Lecidea atrobrunnea, Rhizocarpon geographicum gr. and Sporastatia testudinea on serpentinized ultramafic rocks in an alpine environment

Abstract The effects of biogeophysical and biogeochemical weathering generated by the epilithic lichen species Sporastatia testudinea (Ach.) A. Massal., Lecidea atrobrunnea (Lam. and DC.) Schaer. and Rhizocarpon geographicum gr. on antigorite serpentinites were examined with a petrographic and lichenological approach. Lithotype structure and mineral composition are decisive factors in modulating hyphal penetration which invades up to 2 mm in depth. A microcrystalline fraction composed of fragments of the colonized substratum (antigorite, magnetite, diopside), neoformation minerals typical of serpentine soils (illite, halloysite, vermiculite) and biomineralization products (mainly oxalates), constantly found at the lichen–rock interface, underlines the important role of these crustose lichen species in the pedogenetic processes.

Uranium Biosorption by the Lichen Trapelia involuta at a Uranium Mine

Metal localisation was investigated in the lichenised ascomycete Trapelia involuta growing on a range of uraniferous minerals including metazeunerite [Cu(UO2)2(AsO4)2·8H2O], metatorbernite [Cu(UO2)2(PO4)2·8H2O], autunite [Ca(UO2)2(PO4)2·10H2O] and uranium-enriched iron oxide and hydroxide minerals at the abandoned South Terras mine site, Cornwall, UK. Apothecia from samples collected from waste dumps at the mine have an unusually dark colour that decolorized with NaOCl, an observation which together with Fourier Transform Infrared Spectroscopy of apothecial extracts, suggested the presence of melanin-like pigments. X-ray element mapping and probe traverses across the lichen-rock interface identify the highest U, Fe, and Cu concentrations in the outer parts of melanised apothecia. Accumulation of mineral particulates and complexing with lichen acids are not considered responsible for this since element ratios in the traverses do not correspond with those of likely mineral phases and lichen metabolites are localised in different tissues. Metal biosorption by melanin-like pigments are likely to be responsible for the observed metal fixation. No detectable U or Cu was observed in control samples although Fe showed a similar localisation in some specimens. The high concentrations of mucopolysaccharides and P recorded inside apothecia (within asci containing reproductive spores and hypothecium) suggests that the formation of melanised tissues may help protect vital reproductive tissues from the toxic effects of U and other metals, since the uranyl ion complexes strongly with phosphate species.

Comparative studies of the lichen–rock interface of four lichens in Vingen, western Norway

Sandstone samples from Vingen, western Norway have been analysed to find whether different lichen taxa may explain variations in the degree of weathering at this site. The samples were analysed by high performance thin-layer chromatography (HPTLC)/thin-layer chromatography (TLC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), followed by descriptive statistics and principal component analysis (PCA). The study of the weathering rinds beneath four lichens indicates differences in weathering effect between the studied taxa. Those rinds beneath Ophioparma ventosa, and to a lesser extend Pertusaria corallina, are in general deeper and show a higher degree of mineral dissolution and crumbling of the rock surface, compared to Fuscidea cyathoides and Ochrolechia tartarea. A very high concentration of fungal hyphae within the weathering rind beneath O. ventosa and P. corallina, compared to the other two taxa, may be the cause of the increased biophysical and biochemical weathering. O. ventosa and F. cyathoides contain similar amounts of oxalate, which also in general are much higher than for P. corallina and O. tartarea. The studied taxa also contain different lichen compounds. Differences in content of lichen compounds seem thus to be a more likely explanation for the variations in chemical weathering, than differences in oxalic acid production. In addition to biological mediated physical and chemical weathering, the water holding capacity of lichens may increase the chemical dissolution and frost wedging of rock surfaces. The thallus and the endolithic fungal hyphae bind the partly fragmented rock surface and protect it from abrasion and erosion. However, when the thallus dies, loose mineral grains and fragments from the upper lichen–mineral interface will be removed and a new surface will be exposed and available for colonization and biodegradation. It is thus likely that lichens enhance weathering rates, except at locations with extremely high abrasion, where they may protect the surface.

The occurrence of biomineralization products in four lichen species growing on sandstone in western Norway

High performance thin-layer chromatography/thin-layer chromatography, X-ray diffraction, and scanning electron microscopy analysis of thallus and lichen-rock interface samples, were undertaken to characterize biomineralization products in Fuscidea cyathoides, Ochrolechia tartarea, Ophioparma ventosa, and Pertusaria corallina, growing on sandstone in western Norway. Whewellite (monohydrate form of Ca oxalate) was found in the thallus of all species, but not in any of the weathering rinds beneath the species. A significantly higher amount of whewellite was detected in the thalli of F. cyathoides and O. ventosa than in the other two species. There were only a few differences in whewellite occurrence between the thallus edge and centre samples in the four species. HPTLC/TLC and SEM analysis indicate that lichen compounds occur within the rock beneath some of the lichen specimens. Only divaricatic acid was observed within the weathering rind beneath O. ventosa. No lichen substances were found in the weathering rind beneath F. cyathoides and P. corallina, whereas gyrophoric and lecanoric acids were found in the weathering rind beneath O. tartarea.

Mineralogical Transformation of Bioweathered Granitic Biotite, Studied by HRTEM: Evidence for a New Pathway in Lichen Activity

AbstractThe question of whether clay minerals can be biogenically transformed as a result of lichen activity at the lichen-rock interface remains unresolved. We applied several microscopical and analytical techniques—scanning electron microscopy-back-scattered electron (SEM-BSE), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM)—in an attempt to address this issue. Unaffected granitic biotite and bioweathered material from the granitic biotite and Parmelia conspersa lichen thalli interface were examined using HRTEM after ultrathin sectioning. The n-alkylammonium treatment of ultrathin sections was carried out in order to study the biogenous mineralogical transformation of the biotite. Microsamples proceeding from unaffected biotite zones demonstrated homogenous 10-Å d(001)-value biotite phase. HRTEM images of lattice fringes of samples taken from the lichen-biotite contact zone reveal large areas of both unexpanded (10-A) and randomly and R = 3 distributed expanded (from 14- to 30-Å) layers of phyllosilicates identified as interstratified biotite-vermiculite. Results of artificial biotite weathering (replacement of K by Ca ion) also revealed the biotite-vermiculite phase formation, indicating that K release in biotite is one of the mechanisms responsible for interstratified mineral phase formation. Two parallel processes, physical exfoliation of biotite and inter-layer ionic exchange of K and subsequent vermiculite formation, are the mechanisms for biotite bioweathering induced by lichens.

Application of X‐ray element mapping across the lichen–rock interface

The application of element mapping in the scanning electron microscope with electron probe microanalysis across the lichen–rock interface is described with reference to Trapelia involuta growing on a granite substratum. The preparation of samples containing both organic and mineral components required the development of specialized techniques to maintain both chemical and structural integrity at the 2 μm resolution of the X‐ray element maps. X‐ray element maps show the distribution of entrained rock particles at the lichen–rock interface and chemical localization which is strongly related to anatomical structure for the essential elements S, Fe, Ca, Na, K and P. The ability to map element distribution across the lichen–rock interface has wide‐ranging potential applications in studies such as the biodeterioration of buildings and monuments and the mobilization and uptake of toxic elements from contaminated substrata.

Uranium Accumulation in Lichens

The lichen Trapelia involuta has been found growing directly on the secondary uranium minerals metazeunerite [Cu(UO2)z(AsO4)2.8H20] and meta-torbernite [Cu(UO2)2(PO4)z.SH20] on uraniferous mine spoil heaps. Trapelia specimens present on this spoil have atypically dark brown-black (rather than pale red-brown) fruiting bodies (apothecia), the pigment being restricted to their outer walls and visible in thin section. X-ray element maps for U across transverse sections through the lichen-rock interface show U accumulation principally within the outer fruiting body (apothecia) walls of the lichen compared with their interior. These high U concentrations are not caused by the trapping of mineral particles as reported in previous studies since U:Cu, U:As and U:P ratios within the lichen differ significantly from those of possible trapped mineral phases. Complexing with oxalic acid and secondary lichen products can also be discounted as mechanisms since we identified calcium but no U-bearing oxalates within the apothecial walls. We irrigated sections with NaOC1 confirming the presence of the secondary metabolite, gyrophoric acid within the main lichen body, but not within the apothecia, suggesting that this is also not responsible for the U accumulation observed.