Characterization of mycobiont adaptations in the foliose lichen Xanthoparmelia chlorochroa (Parmeliaceae).

A cross section of the vagrant soil lichen Xanthoparmelia chlorochroa was analyzed using proton microprobe PIXE. Data were used to generate quantitative, two-dimensional element distribution maps for Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, and Sr. Element maps show differential element partitioning between the stratified layers of the thallus. These data document transfer of inorganic nutrients across the thallus to the algal layer. Inorganic particle entrapment was also evident in the element maps. Dense accumulations of calcium oxalate at the junction of the medulla and the algal layer on the order of 10% by dry mass were discovered. Scanning electron microscopy and thermogravimetric analyses were used to characterize the calcium oxalate region. These data provide evidence for possible functional roles of the calcium oxalate layer, including regulation of water and light. Data also provide support for a mutualistic interpretation of the lichen association.