Experimental study of sequences of ectomycorrhizal fungi on birch ( Betula SP.) seedling root systems

Abstract

Birch seedlings on which mycorrhizas of different fungi (primary inoculants) were established in aseptic conditions were transplanted into pots of brown earth supplemented with inocula of other mycorrhizal fungi (secondary inoculants) in a glasshouse study. Leccinum scabrum and Amanita muscaria did not persist as primary inoculants after transplanting seedlings to soil, and did not colonize as secondary inoculants, irrespective of the presence of other mycorrhizal fungi. Lactarius pubescens persisted poorly as a primary inoculant after transplanting and did not colonize seedlings as a secondary inoculant in soil; however, Lactarius-type mycorrhizas sometimes developed from naturally occurring inoculum in soil, especially after seedlings had been subjected to dormancy. Hebeloma sacchariolens and Thelephora terrestris persisted and spread as primary inoculants after transplanting and also colonized seedlings as secondary inoculants. These fungi apparently competed with one another, H. sacchariolens being dominant in a brown earth; but H. sacchariolens was ineffective as either primary or secondary inoculant in sphagnum peat, whereas T. terrestris formed abundant mycorrhizas in peat. Two isolates of Paxillus involutus behaved differently from one another: one isolate did not persist as a primary inoculant and did not colonize as a secondary inoculant whereas the other isolate did not persist as a primary inoculant but colonized seedlings extensively as a secondary inoculant in soil. The results demonstrate important and predictable behavioural differences between mycorrhizal fungi that have been termed “early-stage” and “late-stage” in mycorrhizal sequences on birch. Only early-stage mycorrhizal types were suitable for artificial inoculation of seedlings; they influenced subsequent colonization by some other mycorrhizal fungi but did not facilitate colonization by late-stage types typical of mature tree stands.