Mycorrhizal diversity

Plant mycorrhizal associations are an often neglected, but nevertheless key link in the functioning of ecosystems and are important to sub-arctic willow scrub (Watling, 1992). Previously, assessing the diversity of mycorrhizal fungi has been hampered due to a lack of taxonomic expertise, and the difficulties of relating surface fruiting bodies with below-ground mycelia and root associations. However, recent developments in molecular genetics now offer methodological approaches for the investigation of mycorrhizal fungal diversity in relation to higher-plant diversity, using fungal specific primers and sequence based molecular identification (Gardes & Bruns, 1993; Bruns et al., 1998).

Ectomycorrhizal fungi are important to woody perennials in upland environments where decomposition processes are slow and much of the soil nitrogen is bound in organic matter. We aimed to assess the diversity of ectomycorrhizal fungi associated with Salix herbacea by recording both fruiting bodies appearing above-ground and ectomycorrhizas below-ground. We also investigated the relationship between diversity of ectomycorrhizal fungi and diversity of host genotypes in willows. In addition a field experiment was established to assess the ectomycorrhizal colonization potential of upland soils targeted for restoration.

Fungal pathogen diversity (Rusts)

Willows are particularly susceptible to rust infections (Melampsora spp.), and these can have devastating effects on uniclonal plantations of biomass willows (Helfer, 1992; Pei et al., 1999). The sub-arctic willows are infected by a variety of species (Helfer, 1992), but a detailed understanding of the biology of these pathogens is complicated by difficulties of identification, when not all developmental stages are available to study (the complicated life cycle of rusts involves five spore stages).

As with the mycorrhizal species, fungal specific primers were used to amplify rust DNA and establish a sequence identification database. This diagnostic assay was used to screen the diversity and distribution of rust species occurring on different willow species. In commercial biomass willows there is evidence of inter-clone and inter-specific differences in rust susceptibility (Fritz et al., 1996; Hunter et al., 1996). We aimed to assess variation in susceptibility within and between sub-arctic willow species in the field.