Lichen colonization on stone surfaces is usually associated with biodeterioration processes, due to penetration of hyphal structures and metabolite release, but lichen bioprotection has also been documented, due to an umbrella-like action or the sealing of rock discontinuities related to biomineralization. The balance among these processes depends on many variables and its comprehension is crucial to understand the role of lichens in biogeomorphology and their actual threat to stone heritage conservation. However, stones colonized by lichens have still been mostly examined in terms of affected volumes and physico-chemical modes of interactions, overlooking the overall effects on properties related to surface durability. In this study, the impact of lichen colonization patterns on sandstone was examined beneath thalli of the epilithic species Verrucaria nigrescens Pers., the intermediate epi-endolithic Verrucaria muralis Ach. and the endolithic Protoblastenia incrustans (DC.) J. Steiner. Rock hardness, i.e. a proxy of rock durability, was measured at different depths from the surface using a micro-sclerometer and compared to that of freshly cut surfaces and surfaces exposed, but not colonized by lichens. Mineralogical analyses were performed by X-ray powder diffraction beneath V. nigrescens and V. muralis, in comparison with unweathered rock volumes. Sclerometric analyses quantified a significantly higher decrease of stone hardness beneath V. nigrescens and P. incrustans with respect to V. muralis. A relationship of such species-specific impact with differences in hyphal penetration and patterns of calcite (re-)precipitation was recognized. These results confirm that decisions on lichen removal from stone surfaces should consider each specific behaviour. Moreover, the innovative approach of measuring stone hardness variation in association with the analysis of biomineralization processes contributes to unveil the extension of the sphere of lichen interaction within stone substrate beyond the limit of the hyphal penetration.
Complete tool for submission, evaluation and publication of proceedings for scientific events.
