Abstract
Plants evolve diverse communication systems in adapting to complex and variable environments. Here, we examined the relationship between plant architecture, population density and inter-plant communication within tree species. We tested the hypothesis that trees of species with complex architecture or high population density (high population density: HPD) communicate among conspecifics via volatiles. In addition, we hypothesize that states of mycorrhizal symbiosis (arbuscular mycorrhizal or ectomycorrhiza) which relation to population density can predict the development of interplant communication in trees. We tested induced defense as an indicator of communication in saplings of nine tree species with various complexities of architecture (number of leaves per shoot) and either low (low population density: LPD) or HPD, either exposed for 10 days to volatiles from a damaged conspecific or not exposed. We evaluated the number of insect-damaged leaves and the area of leaf damage on these trees after 1 and 2 months in the field. Most exposed HPD trees had less leaf damage than controls. However, LPD trees did not differ in leaf damage between treatments. These results are partially supported by plant hormone analysis. In addition, the presence of inter-plant communication was positively correlated with both the number of leaves per shoot (complexity of plant architecture) and population density. The analysis which combined results of previous studies suggests that states of mycorrhizal symbiosis predict the development of interplant communication; interplant communication is common in ectomycorrhiza species. These results suggest the importance of plant architecture and population density as well as state of mycorrhizal symbiosis in the development of interplant communications within tree species.