Lichen biodeterioration under different microclimates: An FT Raman spectroscopic study

The FT Raman spectra of lichen-substratum encrustations of Diploicia canescens on a limestone church tower are reported. The presence of calcium oxalate dihydrate in the encrustations was identified from the nu(CO) stretching fundamentals at 1474, 908 and 506 cm(-1) of the oxalate ion. Quantitative measurements were made of the relative amounts of lichen cellulose, characterised by nu(CH) stretching at 2934 cm(-1), pigmentation, characterised by nu(C=C) stretching at 1526 cm(-1) and calcium oxalate dihydrate along radial transects of surfaces of lichen thalli and encrustations. It was found that the biodeterioration of the limestone substratum did not involve the incorporation of particles of the substratum into the central zone of the thallus, unlike other high-oxalate producing lichen species. A preliminary investigation has been made of the relationship between microclimate, in terms of air and wall temperatures and humidity, and the biodeteriorative capability of thalli exemplified by calcium oxalate dihydrate production: it would appear that warmer and drier sites are more conducive to calcium oxalate dihydrate production by D. canescens under these circumstances.