Structural relationship between lichen and carved stonework of Silos Monastery, Burgos, Spain

A study of lichens growing on the cloister of Silos Monastery (Burgos, Spain) was undertaken in order to gain a better understanding of the mechanisms by which lichen thalli alter the surface of monuments. Tiny pieces (flakes) of the stone surface, some of which bore visible thalli of Caloplaca decipiens and Lecanora albescens, were studied with scanning electron microscopy, transmission electron microscopy and X-ray microanalysis. Transmission electron microscopy showed the spatial relationship between the lichen and the rock which forms the abacus of the capital. Deposits of electron dense material, whose chemical compositron revealed a predominance of calcium, were visible among the hyphae as well as in the vicinity of algal cells. Other structures with different elemental composition were also observed. It was possible to observed structures resembling fungal hyphae inside flakes of material which showed no macroscopic evidence of lichens.