Various fungi interact with heavy metals (HM) differently
regarding their binding ability and their tolerance. Besides the ability
of
the fungus to form an extensive extramatrical mycelium, its binding
and transport properties are the most important factors in
ameliorating the effects of HM toxicity on the mycorrhizal symbiosis.
The tolerance of seven ectomycorrhizal fungi to elevated lead
concentrations was tested using agar cultures and the results were
compared to those from liquid culture. Critical toxic
concentrations, where the growth of the mycelium was inhibited to 50%,
were lower in liquid cultures (around 0·2 mm) in
comparison to agar cultures (0·5–2 mm).
The less tolerant fungi in agar culture were Amanita muscaria
and Laccaria laccata, the most
tolerant Lactarius piperatus, Pisolithus tinctorius
and two strains of Suillus bovinus, DB83 from a lead polluted
area and DB84 from a
non-polluted area. Tolerance indices, based on the dry weight of
mycelia from liquid culture, differ from the tolerance indices
obtained from solid culture. L. laccata growth was limited
to a lesser extent than other fungi and the growth of S. bovinus
DB83 was
strongly stimulated at a Pb concentration of 30 μm,
which could indicate lower susceptibility of this strain to low lead
concentrations. The uptake, transport and release of Pb were then studied
with
210Pb tracer using Conway cells with the active
tracer added to the inoculated medium in the centre compartment. The uptake
of Pb by P. tinctorius (1·1% of the added activity) was
much lower than the uptake by L. laccata and S. bovinus
DB83 (6·2 and 5·4% of the added activity respectively). The
same situation
was reflected in the activity of the tracer transported in
the mycelia. Further, the release of transported Pb from mycelia to the
outer
medium differs between L. laccata and S. bovinus
DB83 mycelia, reaching 45 and 10% of the transported activity, respectively,
indicating stronger binding of lead to S. bovinus DB83.
The results of the tracer study are discussed with respect to various
experiments with ectomycorrhizal seedlings and lead.