Ectomycorrhizas and amelioration of metal stress in forest trees

It has often been suggested that ectomycorrhizas ameliorate metal toxicity in forest trees. This paper will present a review of investigations carried out to assess amelioration of metal toxicity by ectomycorrhizas. These investigations have used a number of metals and a range of ectomycorrhizas. In a small number of cases amelioration of metal toxicity could be shown for specific metals by some fungi. In recent investigations on the ability of two species of ectomycorrhizas to improve Cd tolerance in Picea abies, a clear amelioration of Cd toxicity could be shown with Paxillus involutus. This improvement could not be related to decreased Cd uptake. However, in general, evidence suggests that ectomycorrhizas do not universally ameliorate metal toxicity. Amelioration is dependent upon the species and strain of the ectomycorrhiza and the metal being considered. (C) 1998 Elsevier Science Ltd.