Regional scale gradients of climate and nitrogen deposition drive variation in ectomycorrhizal fungal communities associated with native Scots pine

Ectomycorrhizal fungi commonly associate with the roots of forest trees where they enhance nutrient and water uptake, promote seedling establishment and have an important role in forest nutrient cycling. Predicting the response of ectomycorrhizal fungi to environmental change is an important step to maintaining forest productivity in the future. These predictions are currently limited by an incomplete understanding of the relative significance of environmental drivers in determining the community composition of ectomycorrhizal (ECM) fungi at large spatial scales. To identify patterns of community composition in ECM fungi along regional scale gradients of climate and nitrogen deposition in Scotland, fungal communities were analysed from 15 semi-natural Scots pine (Pinus sylvestris) forests in Scotland. Fungal taxa were identified by sequencing of the ITS rDNA region using fungal-specific primers. Non-metric multidimensional scaling was used to assess the significance of 16 climatic, pollutant and edaphic variables on community composition. Vector fitting showed that there was a strong influence of rainfall and soil moisture on community composition at the species level, and a smaller impact of temperature on the abundance of exploration types. Nitrogen deposition was also found to be important, but only when the forest experiencing the highest deposition (9.8 kg N ha-1 yr-1) was included in the analysis. This finding supports previously published critical load estimates for ectomycorrhizal fungi of 5-10 kg N ha-1 yr-1. This work demonstrates that both climate and nitrogen deposition can drive gradients of fungal community composition at a regional scale.