The dominant mycorrhizal type of a forest stand has been shown to affect rates of decomposition and nutrient cycling in soil, which likely influences the relative abundances of various functional groups of fungi. Soils associated with arbuscular mycorrhizal (AM) plants typically have higher rates of litter decomposition, nutrient cycling, and greater availabilities of mineral nutrients compared to soils associated with ectomycorrhizal (ECM) plants. These different nutrient economies, coupled with direct competitive interactions between mycorrhizal and free-living soil fungi, should influence fungal diversity and affect the relative abundances of saprotrophic and pathogenic fungal taxa. Additionally, increased inorganic nutrient availability caused by anthropogenic N deposition may have a particularly strong effect on fungal communities in forests dominated by ECM plants. Understanding the effects of different mycorrhizal types on the broader fungal community may also help explain recent observations of predominantly negative plant-soil feedback for AM plant species and positive feedback for ECM plant species. In this study, we used Illumina sequencing to explore how fungal community composition and function changes along a gradient of mycorrhizal dominance in three temperate hardwood forests. We also tested for the stability of these differences using a long-term, nitrogen deposition experiment.
Results/Conclusions
We found that forest soils associated with AM trees contain a greater diversity of soil fungi, as well as higher abundances of fungal saprotrophs, necrotrophic plant pathogens, and biotrophic plant pathogens, compared to soil associated with ECM trees. Additionally, these groups appear to increase linearly with a gradient of increasing AM dominance. Soil fungal communities associated with our nitrogen deposition experiment were largely unaffected by increased inorganic nitrogen availability, regardless of soil mycorrhizal associations. Overall, the changes in fungal diversity and functional group abundances observed in our study closely follow predicted outcomes based on the different nutrient economies believed to be operating in AM and ECM soil, and demonstrate how dominant mycorrhizal types can influence entire soil fungal communities through nutrient use and competitive interactions. Our findings have important implications for plant-soil interactions and may explain recently identified patterns of plant-soil feedback between tree communities of different mycorrhizal types.