Beyond seedlings: Ectomycorrhizal fungal networks and growth of maturePseudotsuga menziesii

Mycorrhizal networks are conduits for the transfer of resources between hosts. While ectomycorrhizal networks (EMN) are known to influence seedlings, their effect on adult tree growth remains unknown and may have important implications for forest responses to future climates. We used annual basal area increment of trees and previously describedRhizopogon vesiculosusandRhizopogon vinicolorEMNs to examine an association between the number of connections between trees through an EMN and the growth of adult interior Douglas-fir. We compared this relationship for the year the networks were mapped, in 2008, with 8 years previous and 8 years afterward. We also compared the variation in standardized growth (2000-2016) to examine the association between growth variability and EMN variables. Greater growth was positively associated with (a) the number of connections to other trees via aR. vinicolorEMN and (b) the number of genets ofRhizopogon vesiculosisby which a tree was colonized. Variation of growth (2000-2016) was negatively associated with increasing number of connections to other trees viaR. vinicolor. Synthesis. These findings, for the first time, indicate that EMNs may positively influence the growth of adult trees. The difference in tree growth response between the sister fungal species highlights a novel avenue to identify interspecific and intraspecific differences between fungi occurring at different depths in the soil. Our study has important implications when considering the role of EMNs in influencing forest health and mitigating stress from environmental conditions.