Abstract
The colonisation of stone by different organisms often leaves biodeterioration patterns (BPs) on the surfaces even if their presence is no longer detectable. Peculiar weathering patterns on monuments and rocks, such as pitting phenomena, were recognised as a source of information on past colonisers and environmental conditions. The evident inhibition areas for new bio-patinas observed on the marble blocks of the Caestia Pyramid in Rome, recognisable as tracks of previous colonisations, seem a source for developing new natural products suitable for restoration activities. To hypothesise past occurring communities and species, which gave rise to such BPs, we carried out both in situ observations and analyses of the rich historical available iconography (mainly photographs). Moreover, we analysed literature on the lichen species colonising carbonate stones used in Roman sites. Considering morphology, biochemical properties and historical data on 90 lichen species already reported in Latium archaeological sites, we suppose lichen species belonging to the genus Circinaria (Aspicilia s.l.) to be the main aetiological agent of such peculiar BPs. These results seem relevant to highlight the long-lasting allelopathic properties of some lichen substances potentially applicable as a natural product to control colonisation, improving the environmental and economical sustainability of stone restoration.
Highlights
Stone monuments are affected in different ways by organisms and microorganisms, whose metabolic activity and growth can impact them aesthetically, chemically and/or physically, determining biodeterioration phenomena [1,2,3,4,5,6]
Considering morphology, biochemical properties and historical data on 90 lichen species already reported in Latium archaeological sites, we suppose lichen species belonging to the genus Circinaria (Aspicilia s.l.) to be the main aetiological agent of such peculiar biodeterioration patterns (BPs)
We evaluated the potential correlation of lichen species recognised as possible colonisers of the Pyramid with the surfaces noncolonised by cyanobacteria
Summary
Stone monuments are affected in different ways by organisms and microorganisms, whose metabolic activity and growth can impact them aesthetically, chemically and/or physically, determining biodeterioration phenomena [1,2,3,4,5,6]. Studies on the rocks of the Negev desert (Israel) showed differentiable weathering patterns, which were explained by the effects of different environmental exposures, and related to different BPs [13] This information was used for interpreting BPs occurring in several archaeological areas in Israel and demonstrating the existence of different bioclimatic conditions before their burial, which stopped their growths but left their evident tracks [14,15]. In the case of the Trajan column (Rome), a diffuse pitting is still detectable on South-exposed marble surfaces, which had never shown any evidence of living organisms [16,17] Such weathering patterns were interpreted as the consequence of past growths of endolithic communities of cyanobacteria and lichens, occurring in the areas wetted by incident rainfall [16]. Even if the communities are no longer living, due to the climatic changes that have occurred or peculiar environmental conditions in the past, the detected weathering patterns were useful in the understanding of past phenomena [19,20], and they may potentially provide information for the future conservation of stone materials
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