Uptake of Cd-109 by roots and hyphae of a Glomus mosseae Trifolium subterraneum mycorrhiza from soil amended with high and low concentrations of cadmium

Subterranean clover (Trifolium subterraneum L.) in symbiosis with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe was grown in compartmented pots. Side compartments were filled with soil where recently added (1 wk) radio-labelled cadmium (Cd) at three levels of non-labelled Cd could be accessed by either roots or arbuscular mycorrhizal hyphae. All treatments were replicated with non-mycorrhizal plants. After a growth period of 52 d roots and shoots were analysed for Cd-109, and lengths of roots and hyphae in respective labelled compartments determined. Cadmium uptake by roots was not significantly influenced by the mycorrhizal status of the plant. Uptake of Cd from hyphal compartments was higher in mycorrhizal than in non-mycorrhizal plants, corresponding to 96, 127 and 131% of that in non-mycorrhizal plants when 1, 10 and 100 mg Cd kg(-1) was added, respectively. A large proportion of the increased Cd content of mycorrhizal plants was sequestered in the roots. It is concluded that extraradical hyphae of AM fungi can transport Cd from soil to plants, but that transfer from fungus to plant is restricted due to fungal immobilization. No reduction of hyphal growth into soil with up to 20 mg extractable Cd kg(-1) was observed.