Sergio E. Favero-Longo

Revisiting photobiont diversity in the lichen family Verrucariaceae (Ascomycota)

The Verrucariaceae (Ascomycota) is a family of mostly lichenized fungi with a unique diversity of algal symbionts, including some algae that are rarely or never associated with other lichens. The phylogenetic position of most of these algae has not yet been studied and, because morphology-based identifications can often be misleading, molecular data is necessary to revisit their identity and to explore patterns of association between fungal and algal partners. For this reason, the diversity of photobionts in this lichen family was investigated using molecular markers (rbcL and nuSSU) amplified from DNA extracts of lichen thalli and cultured isolates. Although a single algal genus, Diplosphaera (Trebouxiophyceae), was associated with 12 out of the 17 sampled genera of Verrucariaceae, representatives of eight other genera in five orders of the Chlorophyta and one genus in the Xanthophyceae also form lichen associations with members of the family. Fungal genera with simple crustose thalli (e.g. Hydropunctaria, Wahlenbergiella, Bagliettoa) use a high diversity and unusual selection of photobionts. In contrast, fungal genera with more complex thalli (e.g. Placidium, Dermatocarpon) tend to have lower photobiont diversity. Habitat requirements and phylogenetic histories are both partly reflected in the observed patterns of associations between lichenized fungi from the family Verrucariaceae and their photobionts.

Primary succession of lichen and bryophyte communities following glacial recession on Signy Island, South Orkney Islands, Maritime Antarctic

Abstract A directional primary succession with moderate species replacement was quantitatively characterized on Signy Island in zones of a glacial valley corresponding to their age since deglaciation. A continuous increase in diversity and abundance of lichens and bryophytes was observed between terrains deglaciated in the late 20th century, to areas where deglaciation followed the Little Ice Age, and others thought to be ice-free since soon after the Last Glacial Maximum. Classification (UPGMA) and ordination (principal co-ordinate analysis) of vegetation data identified three different stages of development: a) pioneer communities, which rapidly develop in a few decades, b) immature communities developing on three to four century old terrains, and c) a climax stage (Polytrichum strictum-Chorisodontium aciphyllum community) developing on the oldest terrains, but only where local-scale environmental features are more favourable. Multivariate analysis including environmental parameters (canonical correspondence analysis) indicated terrain age as being the dominant controlling factor, with other environmental factors also exhibiting significant conditional effects (duration of snow cover, surface stoniness). These findings not only quantitatively verify reports of the rapid colonization of Maritime Antarctic terrains following recent climate amelioration and associated decrease in glacial extent, but also show how local-scale environmental resistance may slow or even prevent vegetation succession from pioneer to more mature stages in future.

Physical and chemical deterioration of silicate andcarbonate rocks by meristematic microcolonial fungi andendolithic lichens (Chaetothyriomycetidae)

Physicochemical deterioration processes driven by lithobiontic microcolonial fungi (MCF) and endolithic lichens (EL) are still mostly unresolved. Here, the millimetric penetration of MCF strains within silicate and carbonate lithotypes was quantified. The influence of petrographic features in determining hyphal passageways satisfies a model of physical penetration during the early stages of colonization, already described for EL. The MCF and EL secretion of iron-chelating metabolites accounts for iron mobilization in desert-varnish formation, often putatively related to fungal colonization. Increased dissolution of limestone by the model iron chelator desferrioxamine indicates the possible involvement of these MCF and EL secretes in pitting carbonates.

Lichens on asbestos–cement roofs: Bioweathering and biocovering effects

Asbestos-cement roofs, the most widespread sources of airborne, toxic and carcinogenic asbestos fibres, are often colonized by lichens. Since these latter are physical and chemical weathering agents, they have been often considered as significant responsible of disaggregation processes increasing fibre dispersion. Consequently, official guidelines for the management of asbestos often suggest their removal. Weathering and/or covering effects of lichens on asbestos-cement, however, have never been deeply investigated and available procedures to evaluate asbestos-cement aging do not take the biological colonization into account. In this study we show that a 25% lichen cover modifies physical and chemical properties of asbestos-cement sheets containing chrysotile and crocidolite fibres. By innovatively coupling pull up tests and image analysis of linear structures, we show that fibre loss is significantly lower ( approximately 30%) where lichens develop and offer a physical barrier to the fibre detachment. Below the most covering lichens (Acarospora cervina, Candelariella ssp.), chrysotile and crocidolite undergo a partial incongruent dissolution, which in laboratory assays generally determined a reduction of their surface reactivity. Because of their biocovering and bioweathering effects, lichens on asbestos-cement play a role which differs from the current public opinion and the assumptions of some official regulations, acting as effective spontaneous bioattenuation agents.

In vitro receptivity of carbonate rocks to endolithic lichen-forming aposymbionts.

Sterile cultured isolates of lichen-forming aposymbionts have not yet been used to investigate lichen-rock interactions under controlled conditions. In this study mycobionts and photobiont of the endolithic lichens Bagliettoa baldensis and Bagliettoa marmorea were isolated and inoculated with coupons of one limestone and four marbles commonly employed in the Cultural Heritage framework. After one year of incubation, microscopic observations of polished cross-sections were performed to verify if the typical colonization patterns observed in the field may be reproduced in vitro and to evaluate the receptivity of the five lithotypes to endolithic lichens. The mycobionts of the two species developed both on the surface of and within all the lithotypes, showing different penetration pathways which depend on mineralogical and structural features and highlight different receptivity. By contrast, algae inoculated with the coupons did not penetrate them. Observations suggest that the hyphal penetration along intrinsic discontinuities of rocks is a relatively fast phenomenon when these organisms are generally considered as slow-growing. Samples from limestone outcrops and abandoned marble quarries, colonized by the same species or other representatives of Verrucariaceae, showed penetration pathways intriguingly similar to those reproduced in vitro and highlighted that lichen-driven erosion processes only increase the availability of hyphal passageways after a long-term colonization. These results show that in vitro incubation of sterile cultured lichen-forming ascomycetes with rock coupons is a practicable experimental system to investigate the lichen-rock interactions under controlled conditions and, together with analysis in situ, may support decisions on conservative treatments of historical and cultural significant stone substrata.

The Effect of Weathering on Ecopersistence, Reactivity, and Potential Toxicity of Naturally Occurring Asbestos and Asbestiform Minerals

The mechanisms underlying asbestos toxicity mainly rely on experiments performed on “laboratory” fibers, but little data is available on naturally occurring asbestos (NOA). Human exposure to NOA is subject to their ecopersistence and the modulation of their potential toxicity following weathering. The effect of weathering on three fibrous minerals from the Italian Western Alps, chrysotile, tremolite, and balangeroite—a Fe-rich asbestiform mineral—was investigated by mimicking more than 100 yr of physical (freezing–thawing/wetting–drying cycles in a climatic chamber) and biochemical forces (incubation with oxalic acid). Ion release, evaluated by means of inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and variation in chemical composition, evaluated by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), indicated that weathering modified the fibers in the series: chrysotile > balangeroite > tremolite. Kinetics of ion release from the fibers (Mg, Fe, and Si) revealed different ion removal pathways. Tremolite was poorly affected. Chrysotile preferentially released cations up to a plateau, with physical and biochemical forces acting competitively. Conversely, for balangeroite, upon which weathering forces acted synergistically, the initial loss of ions facilitated further dissolution and more Si than Mg was released, suggesting an ongoing collapse of the crystal structure. Depletion of redox-reactive ions produced a significant reduction in fiber-derived •OH radicals (EPR, spin-trapping technique), but the fibrous nature was always retained. Despite weathered fibers appearing less toxic than “stored/laboratory” ones, NOA is to be considered far from safe because of fibrous nature and residual surface reactivity. Risk assessment needs to consider the effect of weathering on exposures. Both tremolite and balangeroite may contaminate, in some areas, chrysotile asbestos. However, in contrast to tremolite, balangeroite exhibits a low ecopersistence, similar to chrysotile behavior. Any contribution of balangeroite to chrysotile toxicity will thus be related to its quantitative occurrence and not to higher structural stability.

Changes in lichen diversity and community structure with fur seal population increase on Signy Island, South Orkney Islands

Abstract Signy Island has experienced a dramatic increase in fur seal numbers over recent decades, which has led to the devastation of lowland terrestrial vegetation, with the eradication of moss turfs and carpets being the most prominent feature. Here we demonstrate that fur seals also affect the other major component of this region’s typical cryptogamic vegetation, the lichens, although with a lower decrease in variability and abundance than for bryophytes. Classification (UPGMA) and ordination (Principal Coordinate Analysis) of vegetation data highlight differences in composition and abundance of lichen communities between areas invaded by fur seals and contiguous areas protected from these animals. Multivariate analysis relating lichen communities to environmental parameters, including animal abundance and soil chemistry (Canonical Correspondence Analysis), suggests that fur seal trampling results in the destruction of muscicolous-terricolous lichens, including several cosmopolitan and bipolar fruticose species. In addition, animal excretion favours an increase in nitrophilous crustose species, a group which typically characterizes areas influenced by seabirds and includes several Antarctic endemics. The potential effect of such animal-driven changes in vegetation on the fragile terrestrial ecosystem (e.g. through modification of the ground surface temperature) confirms the importance of indirect environmental processes in Antarctica.

Spores of lichen-forming fungi in the mycoaerosol and their relationships with climate factors

Fungal particulates are a dominant component of the bioaerosol, but aerobiological studies traditionally focused on a limited set of fungi having relevance as allergens or plant pathogens. This study first analyzes the occurrence of lichen meiospores in the mycoaerosol, quantitatively evaluating in the atmosphere of an alpine environment the occurrence of polar diblastic spores, unequivocally attributable to the lichen family Teloschistaceae. The analysis of air-samples collected one week per month for one year with a Hirst-type sampler displayed a low percentage occurrence of polar-diblastic spores (<0.1%) with respect to the whole mycoaerosol, dominated by Cladosporium. Spearmans correlation tests on aerobiological and climatic data highlighted a strong relationship between the detection of Teloschistaceae spores and rainfall events, excluding seasonal patterns or daily rhythms of dispersion. The fact that all the air-sampled spores were attributable to the species of Teloschistaceae occurring in the site, together with laboratory observations of predominant short range dispersal patterns for polar diblastic and other lichen spores, indicated that sexual reproduction is mostly involved in the local expansion of colonization, dispersal from a long distance appearing a less probable phenomenon. These findings indicated that responses of lichen communities to climate factors, usually related to physiological processes, also depend on their influence on meiospore dispersal dynamics. Spatial limitations in dispersal, however, have to be taken into account in evaluating lichen distributional shifts as indicators of environmental changes.

Image analysis for measuring lichen colonization on and within stonework

The suitability of image analysis by colour-based pixel classification to quantify lichen colonization on the surface of and within marble, travertine and mortar stonework has been investigated. High resolution images of lichenized stonework surfaces were acquired at different field sites using a scanner, thus avoiding invasive surveys, and the percentage cover of lichen species was subsequently measured in the laboratory using dedicated software. Furthermore, microphotographs of polished cross-sections of lichenized marble, travertine and mortar, stained using the periodic acid-Schiff (PAS) method to visualize hyphae, were produced by the same software to quantify hyphal spread within the substratum, a parameter which can be used more successfully than the commonly used depth of hyphal penetration to quantify how much the lichen has affected the conservation of a stone substratum. Significant statistical differences in hue, saturation and intensity (HSI) of the lichen thalli and PAS-stained hyphae, with respect to the lithic substrata, allowed the software to discriminate and quantify the lichen species cover on, and hyphal spread within, the three investigated lithotypes. Since such a quantitative approach highlights the volume of influence of lichens on stonework, where bioweathering processes are likely to develop, it could be used to support decisions on the preservation of our stone cultural heritage.

Indigenous microfungi and plants reduce soil nonylphenol contamination and stimulate resident microfungal communities

Nonylphenol, the most abundant environmental pollutant with endocrine disrupting activity, is also toxic to plants and microorganisms, but its actual impact in the field is unknown. In this study, diversity of culturable soil microfungal and plant communities was assessed in a disused industrial estate, at three sites featuring different nonylphenol pollution. Although soil microfungal assemblages varied widely among the sites, no significant correlation was found with point pollutant concentrations, thus suggesting indirect effects of soil contamination on microfungal assemblages. The potential of indigenous fungi and plants to remove nonylphenol was assessed in mesocosm experiments. Poplar plants and a fungal consortium consisting of the most abundant strains in the nonylphenol-polluted soil samples were tested alone or in combination for their ability to reduce, under greenhouse conditions, nonylphenol levels either in a sterile, artificially contaminated sand substrate, or in two non-sterile soils from the original industrial area. Introduction of indigenous fungi consistently reduced nonylphenol levels in all substrates, up to ca. 70% depletion, whereas introduction of the plant proved to be effective only with high initial pollutant levels. In native non-sterile soil, nonylphenol depletion following fungal inoculation correlated with biostimulation of indigenous fungi, suggesting positive interactions between introduced and resident fungi.