Effects of air pollution and forest regeneration methods on the community structure of ectomycorrhizal fungi

This thesis describes the ectomycorrhizal community and how it is affected by nitrogen fertilization and forest regeneration methods. Fertilizer treatments included ammonium sulphate (NS), lime+P+K+Ca+Mg+S (N-free) and ammonium nitrate, applied in spruce (Picea abies) stands in south Sweden and a pine (Pinus sylvestris) stand in north Sweden. None of the fertilizers decreased the proportion of short-roots colonized by ectomycorrhizal fungi. Estimations of fungal biomass of short-roots in NS and N-free treatments confirmed this. These results contrast with the 60-100% decreases in sporocarp prodution of ectomycorrhizal fungi reported by other investigators. Molecular methods were used to identify ectomycorrhizal fungi on short-roots after testing their applicability in a separate study. N fertilization had a pronounced effect on the species composition on mycorrhizal roots. The decreased sporocarp production of ectomycorrhizal fungi was suggested to depend on a decreased abundance of species sensitive to N, decreased total allocation of carbohydrates to the fungi, and a changed carbohydrate allocation within the fungi. A second study investigated the community structure of ectomycorrhizal fungi in 11 pine stands in central Sweden. Three stands ("O") consisted of 150-year-old, unmanaged forests, and the remaining were 30-40 years old. Of the latter, four were the result of regeneration by planting on clear-cuts ("P"), and four developed under shelterwood trees that were successively removed ("S"). Mycorrhizal roots, sampled in 1995 and sporocarps (in 1995-96) were identified. The number of species found as mycorrhizas or as sporocarps was lowest in P, whereas species richness was similar in S and O. The species compositions of mycorrhizas or sporocarps were least similar between P an O, but more similar between S and O. Between 45-90% of the mycorrhizas were formed by species not observed in the sporocarp inventory. Multivariate analyses indicated that species composition of ectomycorrhizal fungi was correlated with the age of the forest, soil factors which were partly correlated with age and to some extent also type of regeneration method. It is suggested that nitrogen deposition and N-fertilization reduce the diversity of ectomycorrhizal fungi. Effects of forest regeneration methods appear less pronounced, but fungi restricted to old forest may need protection.