LAUSR

Abstract Mycelium of ectomycorrhizal fungi colonizes soil that is extremely heterogeneous in terms of spatial arrangement as well as chemical and biological properties. Here we addressed which of the soil components would have the greatest influence on hyphal development of an ectomycorrhizal fungus, the summer truffle ( Tuber aestivum ). We tested a range of inorganic and organic compounds and bacterial strains isolated from truffle mycorrhizosphere, added to truffle grounds in small compartments accessible exclusively to the hyphae and not to host plant roots. Our results showed stimulation of truffle hyphal growth by high dosis of lime powder, whereas leaf litter had no effect. Further, we recorded significant stimulation of the hyphal growth by several organic compounds (gallic acid, cellulose and calcium formate), whereas no significant stimulation was observed by any of the inorganic compounds or bacterial cultures mixed with an inert carrier. None of the amendments, however, sustained the truffle growth rate recorded in unsterile field soil. These results indicate that the development of hyphae of T. aestivum in soil may well require complex and micro-heterogeneous environment, where specific organic compounds and calcium carbonate play particularly important roles.