ZINC TOLERANCE IN BETULA SPP. IV. THE MECHANISM OF ECTOMYCORRHIZAL AMELIORATION OF ZINC TOXICITY

Abstract

Aseptic cultures of Paxillus involutus Fr. and clones of Betula pendula Roth. and B. pubescens Ehrh. were used in experiments, involving X-ray microanalysis and split-plate culture, to investigate the mechanism of ectomycorrhizal amelioration of zinc toxicity to Betula. Results imply that as the fungal mycelium colonizes fresh soil, zinc is adsorbed to the surface of hyphae, thereby lowering the concentration of zinc in the soil solution surrounding roots. In consequence, less zinc is taken up, and growth is better than in the non-mycorrhizal condition. The results also show that the metal may be adsorbed to electronegative sites in the hyphal cell walls and extra-hyphal, polysaccharide slime. The possible dual role of this slime in fungus/Betula compatibility and the amelioration mechanism is discussed.