Evolutionary relations between mycorrhizal symbiosis and plant-plant communication in trees

Ecological factors that drive the evolution of plant-plant communication via volatile organic compounds (VOCs) have not been elucidated. Here, we examined the relationship between type of mycorrhizal symbiosis (arbuscular mycorrhiza, AM; ectomycorrhizal mycorrhiza, ECM) and plant-plant communication within tree species. We hypothesized that ECM promotes plant-plant communication among conspecific individuals in trees, because it promotes their cooccurrence through positive plant-soil feedback. We tested communication using saplings of nine tree species with either AM or ECM, either exposed for 10 days to volatiles from an injured conspecific or not exposed. We evaluated the number of insect-damaged leaves and the area of leaf damage after 1 and 2 months in the field. Most exposed ECM-associated trees had less leaf damage than controls. However, AM-associated trees did not differ in leaf damage between treatments. We combined our results with those of previous studies and analysed the evolutionary relation between mycorrhizal type and the presence or absence of plant-plant communication within tree species. ECM symbiosis is associated with the evolution of plant-plant communication within species. These results suggest that the evolution of types of mycorrhizal symbiosis associates with the evolution of plant-plant communications within tree species.