THE EFFECT OF ECTOMYCORRHIZAL FUNGI ON ZN UPTAKE AND DISTRIBUTION IN SEEDLINGS OF PINUS-SYLVESTRIS L

Seedlings of pine, infected with two different ectomycorrhizal fungi, Suillus bovinus (Fr.) O. Kuntze and an unidentified isolate (BP), were exposed to various external Zn concentrations. An additional strain o f S. bovinus, cultured on a Zn-enriched medium, was also used. The eff ect of mycorrhizal associations on Zn uptake and distribution within t he plant was determined by AAS. The results show that nonmycorrhizal s eedlings have the capability to control the uptake and translocation o f Zn to the shoot until the external Zn concentration reaches a thresh old level, where no limitation of uptake is possible. Excess Zn is acc umulated in the root system to protect the shoot against toxic tissue concentrations. The effect of an ectomycorrhizal infection on Zn uptak e and distribution depends on (1) the fungal species (2) the external concentration and (3) the Zn content of the fungal culture medium. Und er conditions of low external Zn supply, especially a mycorrhizal infe ction with S. bovinus led to an increased Zn uptake in root and needle s of Pinus sylvestris. Under high external conditions the mycobionts v aried considerably in their capability to reduce the transport of Zn t o the shoot. Only by an infection with S. bovinus the plant was able t o maintain the shoot tissue concentration on a low level. This effect can be enhanced by pretreatment of S. bovinus with high Zn concentrati ons.