Calluna vulgaris L.Hull readily colonises arsenate contaminated mine spoil soils in south-west(SW)England.At these sites, it forms mycorrhizal association with the ericoid ascomycete fungus Hymenoscyphus ericae. The initial aim of this study was to investigate the physiological response of H.ericae populations to arsenate.Mine site populations were found to have evolved arsenate resistance in comparison to the heathland population.This research demonstrates the evolution of arsenate resistance through an enhanced arsenite efflux in populations of H.ericae from As contaminated mine spoil soils. H.ericae also confers arsenate resistance to C.vulgaris. The ecological significance of these findings is discussed. / Doctor of Philosophy (PhD)