Fig. 5

Lichen effect on the total porosity of the Jerusalem stone (sections observed by SEM-BSE). a Petrographic thin section of a fresh fragment, showing porosity internal to bioclasts (§). b Quantitative characterization, based on image analysis, of the total porosity of a 300-μm layer beneath the surface showing the epilithic Variospora aurantia, the endolithic Pyrenodesmia erodens, and absence of lichens (polished cross section 1); a 300-μm layer beneath the surface showing the endolithic Bagliettoa baldensis and absence of lichens (section 2); 300-μm layers at more than 2 mm from the surface (sections 1 and 2); 300-μm layers of fresh fragments as control. For each section, columns which do not share letters are significantly different (ANOVA, Tukey’s test, p < 0.05). c–e BED-C images of section 1: c rock surface (arrow) not colonized by lichen thalli; d rock surface (arrow) covered by a V. aurantia thallus (#); e rock surface (arrow) dissolved by P. erodens (°). f BED-S image of a polished cross sectioned fresh fragment, with bioclasts (§) embedded in a fine-grained calcite matrix. g–h BED-S images of section 2: g rock surface (arrow) penetrated by B. baldensis (*), with hyphae invading the internal porosity of bioclasts (magnification, h). Scale bars = 100 μm (a, c-g), 25 μm (h)