Ectomycorrhizal fungi - Molecular tools to study species and functional diversity

The extramatrical mycelium of ectomycorrhizal (EM) fungi represents a significant component of the ectomycorrhizal (EM) symbiosis, as the mycelium is primarily involved in the uptake of water and nutrients from the soil. The extramatrical mycelium may also actively mobilize nutrients from organic and mineral sources through excretion of enzymes and organic acids respectively. An observation of tunnel-like structures in weatherable mineral grains gave rise to the hypothesis that these were formed by the hyphae of EM fungal species. Tunneled minerals have been found in the weathered E horizon of podzols, a typical soil type for boreal forests. In these forests the EM fungal community is highly species-rich and this thesis describes the vertical distribution of fungal species throughout the podzol profile, with special emphasis on the weathered E horizon. Identification of EM fungal species from podzol horizons through morphological and molecular identification of EM root tips revealed a significant relationship between the EM fungal species composition and soil horizons. The vertical distribution of the EM extramatrical mycelium in podzol horizons was studied with molecular identification techniques based on total soil DNA extracts and a cloning method. The root tip study as well as the mycelial study showed that many EM fungal species exist in the mineral soil that do not occur in the organic layer of a podzol. A high correspondence was furthermore found between the basidiomycete diversity detected by the molecular analysis of root tips and of hyphae. This thesis further describes the use of molecular techniques for the quantification of EM fungal species in soil. By comparing molecular techniques with conventional quantification techniques, it was shown that molecular methods provide tools to determine the biomass of individual fungal species in soil. The molecular methods enabled identification and relative quantification of two EM fungal species separately in a more-species environment and showed consistent results. In conclusion, this thesis demonstrates that molecular techniques facilitate identification and relative quantification of individual soil fungi and in addition highlights the pitfalls of the molecular methodology. As differences in amount and organization of the extramatrical mycelium produced by different EM fungal species may reflect the different ecological roles that the fungi may have, the detection of hyphae initiates possibilities for in situ studies on substrate specificity, niche partitioning and succession of EM fungal species below ground.