Novel Root-Fungus Symbiosis in Ericaceae: Sheathed Ericoid Mycorrhiza Formed by a Hitherto Undescribed Basidiomycete with Affinities to Trechisporales

Ericaceae (the heath family) are widely distributed calcifuges inhabiting soils with inherently poor nutrient status. Ericaceae overcome nutrient limitation through symbiosis with ericoid mycorrhizal (ErM) fungi that mobilize nutrients complexed in recalcitrant organic matter. At present, recognized ErM fungi include a narrow taxonomic range within the Ascomycota, and the Sebacinales, basal Hymenomycetes with unclamped hyphae and imperforate parenthesomes. Here we describe a novel type of basidiomycetous ErM symbiosis, termed ‘sheathed ericoid mycorrhiza’, discovered in two habitats in mid-Norway as a co-dominant mycorrhizal symbiosis in Vaccinium spp. The basidiomycete forming sheathed ErM possesses clamped hyphae with perforate parenthesomes, produces 1- to 3-layer sheaths around terminal parts of hair roots and colonizes their rhizodermis intracellularly forming hyphal coils typical for ErM symbiosis. Two basidiomycetous isolates were obtained from sheathed ErM and molecular and phylogenetic tools were used to determine their identity; they were also examined for the ability to form sheathed ErM and lignocellulolytic potential. Surprisingly, ITS rDNA of both conspecific isolates failed to amplify with the most commonly used primer pairs, including ITS1 and ITS1F + ITS4. Phylogenetic analysis of nuclear LSU, SSU and 5.8S rDNA indicates that the basidiomycete occupies a long branch residing in the proximity of Trechisporales and Hymenochaetales, but lacks a clear sequence relationship (>90% similarity) to fungi currently placed in these orders. The basidiomycete formed the characteristic sheathed ErM symbiosis and enhanced growth of Vaccinium spp. in vitro, and degraded a recalcitrant aromatic substrate that was left unaltered by common ErM ascomycetes. Our findings provide coherent evidence that this hitherto undescribed basidiomycete forms a morphologically distinct ErM symbiosis that may occur at significant levels under natural conditions, yet remain undetected when subject to amplification by ‘universal’ primers. The lignocellulolytic assay suggests the basidiomycete may confer host adaptations distinct from those provisioned by the so far investigated ascomycetous ErM fungi

Mrnka_et al_IJPM_2020_Marigold_article

This is a primary dataset comprising data from which all figures in our IJPM paper were derive

Mrnka_et al_IJPM_2020_Marigold_article

This is a primary dataset comprising data from which all figures in our IJPM paper were derive

Fine roots of Picea abies compensate for drought stress in the rainfall reduction experiment

This study evaluates the influence of repeated artificial drought stress on the fine root charac- teristics – including ectomycorrhizae – of Norway spruce [Picea abies (L.) Karst]. The experimental site consisted of two plots in a mature spruce monoculture stand. The water regime at parts of both plots was regulated by shelters and an isolation trench during vegetation season (spring to autumn) since 2010. Root samples were collected during autumn in 2010, 2012, and 2013. Root analyses revealed the effect of drought stress on mycorrhizal root tips changed over time. While a density of active mycorrhizae was about 34% lower in drought-stressed areas compared to nonstressed (control) areas in 2010, it increased by 15% in 2012 and by 22% in 2013 over both plots. We observed the less pronounced effect of drought on a proportion of active mycorrhizae, but it generally followed the pattern of active mycorrhizae density. The density of nonactive mycorrhizae was not influenced by drought but significantly fluctuated during the course of the experiment. Other root characteristics such as the dry mass of fine roots (< 1 mm), the specific length of fine roots (< 1 mm) and the composition of the ectomycorrhizal community (primarily dominated by Amphinema byssoides, Tylospora fibrillosa, Tylopilus felleus, and Cenococcum geophilum) were also not significantly influenced by drought. Our results indicate the ability of Norway spruce fine roots to com- pensate for repeated drought stress of the intermediate intensity