Our studies are part of a programme of research into possible harmful effects of heavy metal‐contaminated sewage sludge being applied to soils supporting growth of trees. We have shown that ectomycorrhizal fungi vary in their growth response to heavy metals incorporated into agar plates. Lacearia laccata proved sensitive to Cu and Al when the concentration reached only 10 ppm but was tolerant of Zn at 10 ppm. Thelephora terrestris proved highly tolerant of Cu at 100 and 500 ppm in agar plates and Zn even at 1000 ppm. Mycelial growth in liquid media was inhibited between 200 and 400 ppm Cu. Growth of T. terrestris was reduced by 100 ppm Al. Suillus variegatus proved to be the most tolerant of Al on agar plates with growth increasing at least up to 100 ppm. It was sensitive to Cu at 100 ppm (but not consistently) and Zn at 1000 ppm. Abnormal morphological changes were observed in Scots pine mycorrhizas (T. terrestris) subjected to continuous application of Zn and Cu (as sulphates) in pots in the greenhouse. X‐ray micro‐analysis of the mycorrhizas in a scanning electron microscope revealed accumulation of Zn in the mycobiont‐hyphae. The studies indicate problems that might result from addition of excessive amounts of metals to soils with developing trees.
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