The effect of ectomycorrhizae on the uptake of lead by Pinus sylvestris L. seedlings

Abstract

Clean laboratory technology and pure culture techniques were combined to determine the effect of ectomycorrhizae on the uptake of lead by Pinus sylvestris L. seedlings. By culturing the ectomycorrhizal fungus, Pisolithus tinctorius (Pers.) Coker and Couch, in liquid Hagem's medium with different concentrations of lead (0, 50, 250 and 500 ng/g sol), it was determined that the fungus readily takes up lead from such and aqueous medium. It was also determined that the pH of the medium controls the amount of lead in solution that can be taken up by the fungus.

A series of growth studies where Pisolithus was cultured on Hagem's agar indicated that the growth of the fungus is reduced when the lead concentration in the medium is approximately 25 ug/g sol. It was estimated that a lead concentration of approximately 1,000 ug/g sol may completely inhibit the growth of the fungus. Furthermore, it was determined that the acetate ion is inhibitory to the growth of Pisolithus.

By culturing mycorrhizal and non-mycorrhizal seedlings of P. sylvestris and analyzing the seedlings' roots, stems and leaves for their lead concentrations, it was determined that ectomycorrhizae facilitate the uptake of lead. Ectomycorrhizal roots can take up more lead from a vermiculite/hydroponic solution mixture because of their greater surface area and exploration of vermiculite surfaces as well as their increased production of lead solubilizing acids. This additional lead found in mycorrhizal roots, however, does not appear to be translocated to the above ground portions of the seedlings. This increased uptake of lead by mycorrhizal roots is expected to take place in natural soil systems as well.