Volatile organic compounds mediated plant–plant communication in natural beech forest

Background/Question/Methods

Plants respond to stress such as damage by herbivores and pathogens by releasing Volatile Organic Compounds (VOCs) from leaves. Neighboring plants which received the VOCs often induce defense responses. This phenomenon is referred to as volatile mediated plant-plant communication. We found Fagus crenata also exhibits the plant-plant communication in plantations. In natural forests which are consisted of genetically different individual trees, the role of VOCs is unresolved. The objective of the present study was to clarify whether beech exhibit plant-plant communication in natural forests and whether the response to VOCs differ depending on the kin relationship. We conducted two manipulation experiments with different VOCs emission levels in Japan. In both experiments, we measured leaf damage by chewing herbivores and pathogens of neighboring trees at various distances from the VOC sources. In the first experiment with large VOCs' emission-level, we sampled leaves in May from neighboring trees and analyzed the DNA, quantified the plant phytohormones (Salicylic acids and Jasmonic acids), and the expression of genes related to plant defense. To test whether the leaf damage of neighboring trees changed along with the distance from VOC emission sources, we used generalized mixed effect models.

Results/Conclusions

In the first experiment, the best model explaining leaf damages included distance from the source as fixed effects in herbivore damages. While the best model explaining leaf damage included Jasmonic acid and Salicylic acid concentration within leaves as fixed effects in pathogen damage. The ratio of damaged leaves and the accumulation of Jasmonic acid increased with distance. Since we already found the Salicylic acid would accumulate three days after VOCs exposure, we collected the leaves after 3days VOCs were exposed. Jasmonic acid which is antagonistic against Salicylic acid was expected to have fallen at the time. In the second experiment in the western Japan site, the best models included distance as fixed effect in both types of damage. The damage did not change along with distance in the northern Japan site probably due to less VOCs exposure. These results suggest that beech trees exhibit plant-plant communication in natural forests depending on the spatial distance of trees. Trees neighboring VOC emitting trees start to respond defensively through gene expression and phytohormone production, which resulted in less damage by herbivores and pathogens.