The fungal community associated with roots of alpine and arctic Dryas octopetala along a latitudinal gradient

Abstract

The ectomycorrhizal (ECM) dwarf shrub Dryas octopetala is one of the hardiest and most abundant of all woody plant groups in alpine and arctic environments. The main aim of this study was to characterise the fungal communities associated with D. octopetala roots along a latitudinal gradient from Southern Norway to the high Arctic (Svalbard). Twenty-six root systems were sampled at five main localities (13 sub-localities) and the internal transcribed spacer (ITS) amplified from DNA extracts from pooled root samples using fungal specific primers. Twenty-four cloned ITS fragments were obtained from each root system and the taxonomic affinity of the sequences were analyzed by DNA homology searches against UNITE and GenBank, as well as own reference sequences obtained from collected basidiocarps. A total of 138 Operational Taxonomic Units (OTUs) were detected, 76 belonging to Basidiomycota, 59 to Ascomycota, two to Zygomycota, and one to Glomeromycota, demonstrating that an ecologically and phylogenetically diverse array of fungi is associated with the roots of D. octopetala. The most frequently detected taxonomic order was Agaricales, followed by Thelephorales, Cantharellales and Helotiales. The majority of the environmental sequences had taxonomic affinity to well-known ECM genera such as Hebeloma, Cortinarius, Tomentella, and Inocybe. Most of the environmental sequences with affinity to ascomycetes represented ECM, such as Cenoccoccum geophilum and Cadophora finladia, or endophytic fungi including dark septate endophyes (DSE) such as Phialocephala fortinii. These taxa were widespread and found in all but the southernmost main locality. Non-asymptotic species accumulation curves and the occurrence of a high number of singletons indicate that only a small fraction of the fungal diversity was detected. The spatial heterogeneity in the fungal communities associated with D. octopetala was high, both within and between sub-localities and between main localities, but a slight geographic structuring of the composition of OTUs in the root systems was observed. There was no decrease in fungal diversity with increasing latitude, which contrasts observations made in a wide spectrum of other organism groups.