Tell me who your neighbors are: The role of spatial location and tree species identity in determining the ectomycorrhizal community composition of saplings and mature trees in a mixed conifer forest

O_LIThe mutualistic interaction between trees and ectomycorrhizal fungi (EMF) can have a major effect on forest dynamics and specifically in seedling establishment. Both intrinsic (i.e., identity of the sapling) and extrinsic (i.e., the identity of mature trees in the vicinity of the sapling) factors can affect the EMF community composition of young saplings. C_LIO_LIHere, we compared the EMF community composition associated with the roots of young saplings and mature trees of two co-habiting Pinaceae: Pinus halepensis and Cedrus deodara growing together in a planted forest plot, using fungal ITS metabarcoding. C_LIO_LIWe found that the differences between the two sapling groups were mostly attributed to changes in the relative abundance of specific fungal species. Moreover, we found that physical proximity to a specific host species had a significant effect on the community composition of young saplings. However, while no significant differences in sapling size were apparent, the sapling shoot structure was affected by the identity of the nearest mature tree and its unique EMF community composition. C_LIO_LISynthesis: These results suggest that the dynamics of the EMF community are greatly determined by extrinsic factors such as the small-scale distribution of mature trees in the forest, with possible cascading effects on the development of young trees. C_LI