INTERACTIONS WITH JUNIPER ALTER PINYON PINE ECTOMYCORRHIZAL FUNGAL COMMUNITIES

Belowground interactions can affect plants either directly or indirectly via their associated mycorrhizal fungi. However, few studies have experimentally examined the consequences of interspecific root interactions for these important mutualists in the field. We used a trenching experiment to examine how belowground interactions between pinyon pine and one‐seed juniper affected the ectomycorrhizal (EM) fungal communities of pinyon pine. Three major findings emerged: (1) pinyons responded to the reduction of juniper roots with a near doubling of fine root biomass in just two years, (2) this increase in pinyon roots translated into a potential two‐fold increase in EM abundance, and (3) the EM fungal communities of trenched trees differed significantly from controls largely due to a decrease in ascomycete fungi. Because species of EM fungi vary in the benefits they provide, changes in EM communities could have long‐term consequences for host‐plant establishment, growth, and survival. Belowground interactions with juniper may contribute to the high mortality of pinyons and the reduced diversity of EM fungi associated with recent droughts.