Sensitivity to Cd or Zn of host and symbiont of ectomycorrhizal Pinus sylvestris L. (Scots pine) seedlings

Pinus sylvestris seedlings infected with either the ectomycorrhizal (ECM) f ungus Paxillus involutus or Suillus variegatus were exposed to a range of C d or Zn concentrations. This was done to investigate the relationship betwe en the sensitivity of ECM fungi and their host plants over a wide range of concentrations. P. involutus ameliorated the toxicity of Cd and Zn to P. sy lvestris with respect to root length, despite significant inhibition of ECM infection levels by Cd (Cd EC50 [effective concentration which inhibits EC M infection by 50%] values were: P. involutus 3.7 mu g g(-1) Cd; S. variega tus 2.3 mu g g(-1) Cd). ECM infection by P. involutus also decreased Cd and Zn transport to the plant shoots at potentially toxic concentrations and a lso influenced the proportion of Zn transported to the roots and shoots, wi th a higher proportion retained in the roots of the seedlings. ECM infectio n did increase host biomass production, but this was not affected by the pr esence of Cd or Zn. Root and shoot biomass production by P. sylvestris, in both the presence and absence of ECM fungi, was unaffected by Cd and Zn at all concentrations tested.