A single tree species may host dozens of ectomycorrhizal species, exchanging photosynthate for a supply of diffuse and recalcitrant soil nutrients. This promiscuity in fungal associations is not well-understood, but is believed to stem from niche partitioning within the fungal community. We test this hypothesis by looking for turnover in the ectomycorrhizal community associated with one host tree species, Bishop Pine (Pinus muricata), across a California soil chronosequence which supports a plant community ranging from dense forest to “pygmy” trees dwarfed by diminished soil quality.
Using a traditional sequencing approach, we identify 150 operational taxonomic units (a proxy for fungal species) across five soil age classes within the chronosequence, with some trees hosting at least sixteen distinct fungi. The ectomycorrhizal communities differ significantly between each soil age class, with an especially pronounced boundary between the fungal associates of dwarfed trees (on the three oldest soils, where leached iron has formed a water-impermeable hardpan a few meters below the soil surface) and their healthier neighbors (on younger soils). Published information on the fungi which drive this trend suggests key functional traits (e.g., nutrient acquisition strategy, carbon requirement) may, in part, explain community composition. Such results add to evidence of functional niche partitioning as a driver of fungal diversity at the landscape level.