Effects of resource availability on mycelial interactions and 32P transfer between a saprotrophic and an ectomycorrhizal fungus in soil microcosms

Interactions between mycelia of the ectomycorrhizal fungus Suillus variegatus and the wood decomposing fungus Hypholoma fasciculare were studied in soil microcosms. The ectomycorrhizal mycelium extended from Pinus sylvestris seedlings and the saprotrophic fungus grew out into the soil from birch wood blocks of two alternative sizes. Transfer of 32P between the interacting mycelia was measured non-destructively using electronic autoradiography. The outcome of the interactions was clearly affected by the size of the wood blocks. In systems with large wood blocks (1.6 cm3) the wood decomposer fungus overgrew the mycelium of the mycorrhizal fungus whereas in systems with small wood blocks (0.44 cm3) the mycorrhizal mycelium overgrew the wood decomposer fungus. The saprotrophic fungus was able to capture significantly more 32P from labelled mycorrhizal mycelium when growing out from larger wood blocks. The mycorrhizal fungus was able to capture significantly more 32P from labelled saprotrophic mycelium when the wood blocks were smaller.