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

A cross section of the vagrant soil lichen Xanthoparmelia chlorochroa was a nalyzed using proton microprobe PIXE. Data were used to generate quantitati ve, 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 elem ent partitioning between the stratified lavers of the thallus. These data d ocument transfer of inorganic nutrients across the thallus to the algal lav er. Inorganic particle entrapment was also evident in the element maps. Den se 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 elect ron microscopy and thermogravimetric analyses were used to characterize the calcium oxalate region. These data provide evidence for possible functiona l roles of the calcium oxalate laver. including regulation of water and lig ht. Data also provide support for a mutualistic interpretation of the liche n association.