Comparative studies of the lichen–rock interface of four lichens in Vingen, western Norway

Abstract

Sandstone samples from Vingen, western Norway have been analysed to find whether different lichen taxa may explain variations in the degree of weathering at this site. The samples were analysed by high performance thin-layer chromatography (HPTLC)/thin-layer chromatography (TLC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF), followed by descriptive statistics and principal component analysis (PCA). The study of the weathering rinds beneath four lichens indicates differences in weathering effect between the studied taxa. Those rinds beneath Ophioparma ventosa, and to a lesser extend Pertusaria corallina, are in general deeper and show a higher degree of mineral dissolution and crumbling of the rock surface, compared to Fuscidea cyathoides and Ochrolechia tartarea. A very high concentration of fungal hyphae within the weathering rind beneath O. ventosa and P. corallina, compared to the other two taxa, may be the cause of the increased biophysical and biochemical weathering. O. ventosa and F. cyathoides contain similar amounts of oxalate, which also in general are much higher than for P. corallina and O. tartarea. The studied taxa also contain different lichen compounds. Differences in content of lichen compounds seem thus to be a more likely explanation for the variations in chemical weathering, than differences in oxalic acid production. In addition to biological mediated physical and chemical weathering, the water holding capacity of lichens may increase the chemical dissolution and frost wedging of rock surfaces. The thallus and the endolithic fungal hyphae bind the partly fragmented rock surface and protect it from abrasion and erosion. However, when the thallus dies, loose mineral grains and fragments from the upper lichen–mineral interface will be removed and a new surface will be exposed and available for colonization and biodegradation. It is thus likely that lichens enhance weathering rates, except at locations with extremely high abrasion, where they may protect the surface.