Host plant genetics of a dominant tree, Pinus edulis, have a strong influence on the community composition of associated ectomycorrhizal fungi

Ectomycorrhizal fungi (EM) have been shown to increase water and nutrient uptake of the host plant, thereby helping to alleviate the effects of environmental stress.  Recent work has shown that the composition of the EM community can be more important than abundance in determining the benefits received by the host plant.  Therefore, the role host plant genetics can play in determining EM community composition becomes increasingly important in understanding this mutualistic relationship.  Here we used a 20+ year field experiment and a green house experiment to examine the differences in EM communities between mature pinyon pines (Pinus edulis) which have a genetic resistance or susceptibility to chronic attack by a keystone herbivore.   Our findings show: 1) EM Community composition was different between resistant and susceptible trees. 2) These differences had a genetic influence as EM communities of pinyons which have had the keystone herbivore experimentally removed remained similar to EM communities of susceptible trees.  3) These patterns remained constant across multiple years. 4)  EM communities of pinyon seedlings grown from resistant seeds were different from EM found on seedlings grown from susceptible or insect removal seeds. 5)  The EM of seedlings was a subset of EM found on adults for all three treatments.  Our results provide evidence that plant genetics can influence associated communities, thereby creating an extended phenotype.  The tree’s control of EM communities could feedback to influence the magnitude of the mutualism, as well as affect the ability of the tree to adapt to future climate change.