Tolerance to photoinhibition within lichen species is higher in melanised thalli

Abstract

Some lichenized ascomycetes synthesize melanic pigments when exposed to ultraviolet light and high solar radiation. Here, we used chlorophyll fluorescence in order to test the effect of melanisation on the ability of the lichens Cetraria islandica, Lobaria pulmonaria, Peltigera aphthosa, P. membranacea, Pseudocyphellaria gilva, and Sticta sublimbata to tolerate high-light stress. For each species, melanised and pale thalli were selected from relatively exposed and shaded individuals of the same population. For all species, melanised thalli displayed significantly less photoinhibition than pale thalli following a controlled exposure of hydrated thalli to high light. Melanised thalli were less photoinhibited than pale thalli in lichens from both high light and more shaded habitats, and those that possess either green-algal or cyanobacterial photobionts. Photoinhibition also occurred when dry lichens were exposed to high light; melanised thalli showed again less photoinhibition. Melanised thalli are less sensitive to the adverse effects of high light.