Succession of mycorrhizal fungi on birch: infection of seedlings planted around mature trees

Non-mycorrhizal seedlings ofBetula pendula were planted around an 11-year old tree ofB. pubescens in an experimental plot at Bush Estate, south of Edinburgh. Half (23) of the seedlings were in untreated planting positions and half (24) in positions that had been cored to sever connections of the roots with the parent tree. After 17 weeks, seedlings in the non-cored positions bore mycorrhizas mainly ofLactarius pubescens whereas mycorrhizas of this species were uncommon on seedlings in cored positions. Much smaller and usually non-significant differences were found with respect to other mycorrhizal types in cored and non-cored positions. It is concluded thatL. pubescens infected seedling roots by means of mycelial strands which must remain attached to the parent tree (food base) in order to infect. The significance of the results for the concept of early-stage and late-stage mycorrhizal fungi is discussed.