Distribution and identification of ectomycorrhizal and insect pathogenic fungi in Icelandic soil and their mediation of root-herbivore interactions in afforestation

Abstract

The objectives of the studies in this thesis were to study the distribution and to identify ectomycorrhizal (ECM) and insect pathogenic fungi (IPF) in native Icelandic birch woodlands and eroded (non-vegetated) soils. Furthermore, to study the mediation of these two beneficial soil fungal groups of plant-herbivore interaction in a model system, which consisted of tree seedlings, Otiorhynchus larvae, IPF and ECM fungi.The study was divided into three steps: 1) mapping the distribution and identifying these target soil beneficial fungi in Icelandic soils originating from birch woodlands, heath land and eroded areas, 2) studying the effects of ECM and IPF fungi on Otiorhynchus sulcatus larvae under controlled situations, and 3) studying the interaction among soil beneficialfungi, Otiorhynchus larvae and tree seedlings in representative afforestation sites.Both ECM and IPF were identified in vegetated ecosystems, whereas no IPF were recorded in eroded ecosystems that also supported significantly lower occurrence of ECM. The low fungal occurrence was reflected in poorer birch seedling performance in eroded soil.Three IPF species were identified: Isaria farinosa, Beauveria bassiana and Metarhiziumanisopliae, the latter two species were not previously found in Icelandic soil. Preliminary phylogenetic analysis targeting internal transcribed spacer (ITS) sequences of the major ribosomal gene of mycorrhizal fungi from mycorrhizal birch root tips revealed three main phylogenetic groups: two Basidiomycetes (Hebeloma and Cortinarius) and one Ascomycetes group, of these Hebeloma and Ascomycetes were more common.Inoculation with forest soil, IPF and certain ECM species had negative effects on survival of O. sulcatus under controlled conditions, thus highlighted the importance of careful selection of fungal species used as inoculants in the biological control of Otiorhynchus.The importance of inoculate selection and the need to understand the interaction between the inoculants and native soil biota were further demonstrated under field conditions, where habitat specific, differential root damage response to inoculation was detected.