08 - Studia Geobotanica. An international journal - Vol. 8 (1988)

ENDOLITHIC LICHENS ON LIMESTONE MONUMENTS - This paper briefly illustrates the main features of endolithic lichens growing on limestone, with particular regard to some species which have been found growing on monuments. The action of endolithic lichens on stone is also discussed, with some remarks on the possible harmful effects of the application of biocides to remove endolithic lichens from monuments.

Protective agents are increasingly used for the preservation of stone monuments. Once applied to the rock, they constitute a veritable new substrate. Very little is known on the biological cycles which could develop on treated surfaces. This paper presents a synthesis on the main properties of protective agents, with particular regard to those of biological relevance; the results were obtained on the basis of multivariate analysis of solubility data. The aim of the paper is to provide biologists with an information basis for studies of biogenic cycles on treated surfaces.

Data on lichen presence on some monuments from Piedmont and Aosta Valley are reported. Sampling techniques, chosen on the basis of lithological characteristics of the substrata are described, and the ecological significance of the identified species is discussed. Preliminary data indicate that the majority of the species are neutro-basiphytic and rather nitrophytic, xerophytic and photophytic. Finally, most species appear to belong to the Caloplacion decipientis alliance.

Air pollution has a direct influence on stone decay but also and indirect one by favouring lichen development. This is specially perceptible for nitrophilous lichens which proliferate on rainexposed walls. Thus an historical monument, Notre-Dame de l'Epine's Basilica, was colonized by nitrophilous lichenic population between 1975 and 1980. These nitrophilous species with orange and yellow thallus are responsible for the disfigurement of the Basilica. The spread of nitrophilous lichenic populations is related to a recent increase in the use of fertilizers and, above ali, to the recent methods of spraying fertilizers.

This paper investigates the colonization of concrete tiles by the lichen Caloplaca aurantia in a rural, non-polluted settlement in Israel. The percentage colonization by this crustose Iichen on roof tiles 30, 45, and 60 years old was found to be 2.464 ± 0.732%, 22.972 ± 7.311% and 48.515±6.781% respectively. Scanning Electron Microscopy (SEM) revealed that spherical cells of a unicellular green alga, probably Trebouxia colonize pits on the weathered surface of the very same concrete tiles, as do also the ascopores of C. aurantia. In many of the pits, the ascospores arrange in clusters of 8 units. Fungal hyphae were observed close to ascopores and to the free algal cells.

34 floristic releves concerning epilithic lichens have been carried out in 6 archaeological sites in the surroundings of Rome, on different types of substrate. 52 lichen species have been recorded. The matrix of the releves and of the species has been submitted to programs of multivariate analysis (classification and ordination); the results allow to distinguish 5 main community-types and to order the species according to their degrees of acidophytism and nitrophytism.

The archaeological area in Fiesole, where a local sandstone (Pietra Serena) was mainly used, was taken into consideration with the purpose of investigating the mechanical and chemical alteration possibly due to lichen growth. The taxonomic data allowed identification of almost 40 species. Distribution data allowed definition and localization of the most frequent species, therefore permitting a choice of those to be taken into consideration in relation to their effect on the stone. Observation of stone specimens under optical and scanning electron microscopes showed the morphology of mechanical alterations caused by the growth of some lichen species. The map of distribution of calcium determined by analysis carried out under SEM equipped with an energy dispersive X-ray spectrometer (EDS) showed that some species cause modification of the mineralogical stone composition. Moreover, analyses by X-ray diffractometry, in connection with the above results, allow the identification of the production of calcium oxalate due to tlhe growth of some species.

The lichen vegetation of the Cathedral of Orvieto (Centrai ltaly) has been studied on the basis of 29 phytosociological releves carried out on different parts of the church, and on different substrates. The species by releves matrix has been submitted to classification and ordination to detect different community-types and to study possible ecological gradients. The ecology of the community-types has been studied by means of the ecological indices derived from Wirth (1980). The main causes of lichen growth in different parts of the church, the main aesthetic damages, and the possible measures for eliminating and preventing lichen growth are discussed.

The biocorrosion and biodeterioration of limestone and sandstone by epilithic and endolithic lichens was studied using the maceration and the casting-embedding techniques. The investigations revealed alterations on the rock surface, characterized by biocorrosive pitting, etching patterns, imprints of the fruiting bodies, boring channels and mucilaginous etching figures. Moreover, the inside of the rock is penetrated by extensive and compact networks of the lichenized fungal hyphae. These biodeteriorations are positively correlated to the physical and chemical actions of the lichen involved as well as to the nature of the rock.

A black and white mosaic of the Neptune's house, located in the 2nd century Roman city Italica, was investigated in order study the lichen colonization of tesserae and mortars. Different strategies were observed. They lead to colonization of mosaic in such an extent that lichens clothe the represented figures, masking and affecting the esthetic value of this work of art.

The wheathering ability of Aspicilia contorta thalli with respect to their substrate, a marble tombstone, was studied by conventional, fluorescence, polarized and electron scanning microscopy. Our observations can help to visualize the mechanical fracturing and some product of the lichen metabolism which can affect the mechanical and chemical stability of the substrate.

An appraisal is made of the part played by lichens in the deterioration of stonework. Stone- and artwork in exposed and partially enclosed environments of Central Italy were examined in detail to identify those substrata most vulnerable to lichen attack. Assessment of relationships between particular species and the physical and chemical nature of their substrata was carried out in order to determine the relative importance of lichens in biodeterioration processes obtaining in specific circumstances, and to establish those species responsible for disfigurement and those causing actual destruction. Particular attention is paid to recent environmental changes conducive to increasing detrimental invasion of terracotta, mortar and painted plaster, and reference is made to examples of building materials, statuary and other ornamental carvings, terracotta pots and frescoes, both those in situ at Ostia Antica, Rome and Caprarola (Viterbo) and those relocated in open-air museums, etc.