Initially non-mycorrhizal seedlings of birch (Betula pendula Roth.) were grown for a season around two 11-year-old birch trees on an experimental site south of Edinburgh. Some seedlings (non-isolated) were planted in undisturbed positions, others (trenched) in volumes of soil isolated from the mature tree by trenches, and yet others (cored) in cores of soil (8 × 10 cm diameter) that had been removed and replaced immediately.
Mycorrhizas of Lactarius pubescens (Fr. ex Krombh.) Fr., Lactarius glyciosmus (Fr. ex Fr.) Fr., and Leccinum scabrum (Bull. ex Fr.) S. F. Gray and Leccinum roseofracta Watl. developed abundantly on the non-isolated seedlings but usually very poorly on the trenched and cored seedlings. That some development of Leccinum mycorrhizas occurred in trenched areas is attributed to incomplete severance of roots. In contrast, mycorrhizas of other fungi, for example Hebeloma spp. and Inocybe spp., developed most abundantly on trenched and cored seedlings rather than on non-isolated seedlings.
The results demonstrate an important difference between types of ectomycorrhizal fungus. Lactarius and Leccinum spp. seem to depend on a continuing supply of photosynthate from a mature tree in order to colonize seedling roots, whereas several other mycorrhizal fungi show no such dependence. The results also indicate an important role for mycelial strands in establishment of mycorrhizas by some fungi (Lactarius pubescens and Leccinum spp.) and thus parallel previous reports on the importance of mycelial strands in colonization of substrata by saprophytic and pathogenic fungi.