COS 131-6 - CANCELLED - Ericoid Shrubs Modify the Functional Composition of Soil Fungal Communities Across an Arbuscular to Ectomycorrhizal Tree Dominance Gradient in a Temperate Forest

Abstract: Differences between arbuscular and ectomycorrhizal trees can strongly influence forest ecosystem processes, including soil organic matter accumulation, decomposition rates and nitrogen availability. Ericoid mycorrhizal (ErM) fungi, which associate with understory shrubs in ~70% of temperate forests, also have the capacity to shape nutrient cycling by slowing decomposition rates and intensifying nitrogen (N) limitation in forests. Yet how understory ErM shrubs modify the influence of arbuscular versus ectomycorrhizal trees has been little researched. Moreover, the extent to which aboveground inputs and/or belowground fungal interspecific species interactions shape soil organic matter formation and nutrient retention remains unclear.

Our study analyzes changes in the depth distributions of fungal communities in paired subplots with and without ErM shrubs across an arbuscular to ectomycorrhizal gradient at an eastern temperate forest. In each subplot, we collected soil samples from three depths: the organic horizon (Oa), surface mineral horizon (0-10cm), and subsurface mineral horizon (cumulative depth of 30cm). We hypothesize that (1) ErM fungi will have a higher relative abundance under ErM shrubs in the Oa horizon; (2) the presence of ErM shrubs will reduce the richness and diversity of saprotrophs and ectomycorrhizal fungi in the Oa horizon, but not in deeper horizons; and (3) ErM shrub presence will be associated with lower EcM relative abundance in the Oa and surface mineral horizon.

Ericoid mycorrhizal shrub presence strongly modified soil fungal communities taxonomically and functionally across the tree mycorrhizal dominance gradient. We found that soil depth was associated with a decrease in ErM fungal relative abundance but observed no change in the relative abundance of ErM fungi in the presence or absence of ErM shrubs. In the subsurface mineral horizon, ErM fungal relative abundance decreased with increasing EcM tree dominance. Whole community, saprotrophic and EcM fungal richness decreased under ErM shrubs, and this effect was strongest in the Oa horizon. Ectomycorrhizal tree dominance, on the other hand, had no effect on fungal species richness but was associated with a higher relative abundance of EcM fungi across all depths and a lower relative abundance of saprotrophs in the subsurface mineral horizon. Finally, ErM shrub presence decreased the relative abundance of EcM fungi and increased saprotrophic fungal relative abundance in the subsurface mineral horizon. Our study shows that fungal composition is modified by both depth and dominant tree mycorrhizal associations and that the presence of ErM shrubs can modulate these relationships in temperate forests.