Temperate eucalypt forest decline is linked to altered ectomycorrhizal communities mediated by soil chemistry

Eucalypt forest decline has a complex aetiology often linked to altered soil chemistry caused by environmental disturbances. Forest decline has also been linked to alterations in ectomycorrhizal (ECM) fungal communities, which are imperative for nutrient transfer and affect ecosystem productivity and health. Our aim was to determine the influence of soil chemistry on ECM fungal communities and tree health in declining temperate eucalypt forests. We hypothesise that forests with changed soil chemistry, in particular altered nitrogen cycling associated with forest decline, supports unique ECM fungal communities. ECM communities from twelve Eucalyptus delegatensis forest plots were characterised by DNA sequencing of root tip and sporocarp samples. Tree health and nutrient concentrations from soil and foliage samples were quantified for each plot. Multivariate and regression analyses and t-tests were used to determine ECM fungal community differences between forest health classes, and identify which soil variables were important for defining these communities. Elevated available soil nitrogen and soil acidity were associated with severely declining forest. Soil pH, nitrate and organic carbon significantly explained the majority of variation in ECM fungal community composition and structure, which differed between moderately and severely declining forest. Russulaceae species richness was greatest in acidic soils (severely declining forest) while Cortinariaceae species richness was greatest in soils with lower concentrations of soil nitrate (moderately declining forest). Total ECM fungal richness was inversely related to available soil phosphorus and soil nitrate. Thus, altered soil chemistry associated with eucalypt forest decline mediates changes in the ECM fungal community. Forest management must consider the role of disturbance in maintaining suitable soil conditions for symbiotic fungi which are important for maintaining healthy eucalypt forest and restoring declining forest ecosystems.