Ectomycorrhizal protection of Pinus sylvestris against copper toxicity

Change in the copper (Cu) sensitivity of Pinus sylvestris is presented, in response to the ectomycorrhizal fungi, Suillus bovinus and Thelephora terrestris, common mycobionts on metal contaminated sites. Seedlings grown under phosphorus (P) limitation were exposed to a range of Cu concentrations. Plant and fungal development, P nutrition, sorption of Cu on roots and external mycelia as well as transfer of Cu to shoots were assessed. Root growth and P nutrition were severely inhibited in nonmycorrhizal pines at elevated Cu compared with mycorrhizal plants. Excess Cu had little effect on the development of mycorrhizal roots and mycelia. Thelephora terrestris was less sensitive to Cu stress than S. bovinus. The extraradical mycelium of S. bovinus retained large amounts of Cu. However, binding of Cu in fungal tissue was not a prerequisite for low Cu sensitivity since T. terrertris absorbed considerably less Cu that S. bovinus. Both ectomycorrhizal fungi protect P. sylvestris against Cu toxicity; a benefit that was not due to a metal dilution effect. The mechanisms of mycorrhizal amelioration of Cu toxicity are probably diverse and species-dependent.