Anthropic effect on the lichen colonization in building stones from cultural heritage

In this study the effect of human urine on lithobiontic microorganisms colonizing dolostones from a historic quarry (Redueña, Madrid, Spain) was evaluated in situ by means of a field experiment. The application of the bioproduct was performed by directly spraying onto the rock surface of the quarry front during 8 weeks. After the treatment, the ultrastructure of Verrucaria nigrescens was analysed by Scanning and Transmission Electron Microscopies (SEM and TEM). The study samples showed alterations of the upper cortex fungal cells and altered algal chloroplast. On the surface of the thalli enrichment in phosphorous (P) was also detected by energy dispersive X-ray spectroscopy (EDS). The main result of the field experiment was the alteration of the upper cortex of the lichen thalli leaving unprotected algal cells exposed to environmental conditions. This process might produce in the long term a shift in the lichen community.