Spatial characteristics of volatile communication in lodgepole pine trees: Evidence of kin recognition and intra-species support.

Plant interactions using volatile organic compounds, particularly in the context of kin recognition have received considerable attention in recent years, but several discrepancies and conflicting results have restricted our understanding. We propose that some of these discrepancies in literature are in part due to integral spatial characteristics of sites, and plant attributes. Chemotypic plasticity is commonly used to characterize kin, particularly in conifers. We studied constitutive and induced monoterpene chemotypes of non-attacked lodgepole pine trees within 30 m radii of pine trees attacked by mountain pine beetle. We tested the effects of volatile compounds emitted from the attacked trees on the non-attacked trees by challenge inoculations with a mountain pine beetle associated fungus. We found no relationship between constitutive monoterpene concentrations of the non-attacked trees and distance or direction from the attacked trees or site aspects. In contrast, the effects of volatile compounds were evident after inoculations, depending on distance from the attacked trees and site aspects. However, these interactions only emerged among chemotypically related trees. These results suggest that plants discriminate between chemical cues from kin and strangers, and the emitters likely aid only chemotypically related plants by emitting specific blends of volatiles that can only be deciphered by the receiving kin. These results further demonstrate the importance of incorporating spatial characteristics of sites and plant attributes in studies aimed at investigating intra-species interactions using volatile organic compounds.