Sequences and interactions of mycorrhizal fungi on birch

Summary Soil cores collected under a birch tree (Betula pubescens) on an experimental plot showed a progressive change in types of sheathing mycorrhiza with distance from the tree base. Seedlings grown in cores in a glasshouse also developed different mycorrhizal types depending on distance from the tree at which the cores were taken, but the types on seedlings were often different from those in the parent cores. When cores were taken directly beneath fruitbodies and sown to birch in a glasshouse, seedlings developed mycorrhizas of Laccaria, Inocybe and Hebeloma in cores from beneath these fruitbodies, but they seldom developed Lactarius mycorrhizas and never developed Leccinum mycorrhizas in cores taken beneath these fruitbodies. Similarly, when seedlings were grown in soils supplemented with vermiculite-peat inocula in a glasshouse, Laccaria and Hebeloma readily formed mycorrhizas, butLactarius pubescens seldom did so and Leccinum andAmanita muscaria never dit so. Yet all these fungi form mycorrhizas on birch seedlings in aseptic conditions.The results suggest a distinction between early stage and late stage mycorrhizal fungi of birch. Early stage fungi readily infect seedlings from resident or introduced inoculum in normal, unsterile soil, whereas late stage fungi do not readily form mycorrhizas in these conditions.