Effect of metal stress on photosynthetic pigments in the Cu-hyperaccumulating lichens Cladonia humilis and Stereocaulon japonicum growing in Cu-polluted sites in Japan

• Stereocaulon japonicum and Cladonia humilis are Cu-hyperaccumulating lichens.
• Pigment concentrations in Cu-polluted samples differed from those in control samples.
• No correlations were observed between Cu and pigment concentrations.
• High negative correlations were found between Al and pigment concentrations.
• Secondary metabolite concentrations in C. humilis are not influenced by Cu stress.

To understand the ecology and physiology of metal-accumulating lichens growing in Cu-polluted sites, we investigated lichens near temple and shrine buildings with Cu roofs in Japan and found that Stereocaulon japonicum Th. Fr. and Cladonia humilis (With.) J. R. Laundon grow in Cu-polluted sites. Metal concentrations in the lichen samples collected at some of these sites were determined by inductively coupled plasma mass spectroscopy (ICP-MS). UV–vis absorption spectra of pigments extracted from the lichen samples were measured, and the pigment concentrations were estimated from the spectral data using equations from the literature. Secondary metabolites extracted from the lichen samples were analyzed by high-performance liquid chromatography (HPLC) with a photodiode array detector. We found that S. japonicum and C. humilis are Cu-hyperaccumulating lichens. Differences in pigment concentrations and their absorption spectra were observed between the Cu-polluted and control samples of the 2 lichens. However, no correlation was found between Cu and pigment concentrations. We observed a positive correlation between Al and Fe concentrations and unexpectedly found high negative correlations between Al and pigment concentrations. This suggests that Al stress reduces pigment concentrations. The concentrations of secondary metabolites in C. humilis growing in the Cu-polluted sites agreed with those in C. humilis growing in the control sites. This indicates that the metabolite concentrations are independent of Cu stress.