The influence of silver birch vegetation on the metal availability in mining affected substrate and mycorrhiza supported tree metal tolerance : an attempt of a holistic view on the system substrate fungi tree The work aimed the experimental study of the metal bioavailability in soil and soil solution under the influence of birch vegetation in a mesoscale pot experiment. The substrate used therein originated from a mining affected site that was mainly contaminated with Al and Cu and vast free of vegetation despite stands of silver birch (Betula pendula). Natural birch saplings from this site adapted to harsh abiotical conditions were transplanted to the pots and grown therein for two growing seasons opposed to an unplanted control. The pots were specifically equipped for the highly time and depth resolved monitoring of physico chemistry and metal concentrations in soil solution. The experiment was designed as closed system which allowed the complete quantification of inputs and outputs. The substrate solution monitoring revealed a pH buffering effect of the birch roots. This increase of the rhizosphere pH was attributed to the release of dissociated organic acids into the root apoplast and their subsequent protonation in order to attenuate harmful effects of increased acidification like Al rhizotoxicity. The root induced pH buffering resulted in a decrease of the Al and Cu concentrations in the substrate solution. Additionally the accumulation in the tree root biomass was assumed as a further potential sink for their availability in solution. The total mass balances of the metals in the substrate were not shifted which indicated a lacking extraction by the birch vegetation. Mycorrhizal fungi associated to the tree roots were shown to accumulate high amounts of Al in their hyphae and had therefore a filter like function for that metal as revealed by micro PIXE analysis. In contrast Cu was incorporated in the roots and not accumulated in the fungal biomass. Due to the substrate contamination the diversity of mycorrhizal fungi was restricted to merely three dominant species.