Plant and fungus material
Half-sib seeds of Pinus sylvestris were surface sterilized in
30% H2O2 for 15 min, sown in a 1/1 (v/v) mix of vermiculite
and perlite and watered with a balanced nutrient solution
(Ingestad et al. 1986). The weight proportions of the macronutrients
in the solution were 100 N/60 K/18 P/6 Ca/6 Mg/9 S.
After 10 weeks, plants were selected for uniformity and inoculated
with a mycorrhizal fungus or left uninoculated. Three
ectomycorrhizal species were used for inoculation: Thelephora
terrestris (24 plants), Suillus bovinus (24 plants) and
Scleroderma citrinum (12 plants). For inoculations, mycorrhizal
fungi were grown in 10-cm diameter plastic petri dishes
containing modified Melin-Norkrans agar medium covered
with sterile cellophane sheets. Once the mycelia had covered
most of the cellophane surface, the root system of a selected
seedling was spread over the young mycelia and a thick filter
paper (9 cm in diameter), soaked in Ingestad’s nutrient solution,
was used to cover the roots and mycelia. Control plants
were treated in the same way, except that their roots