Characterization of wound responses of stems of paper birch (Betula papyrifera) and European white birch (Betula pendula)

Abstract

Plants respond to feeding injury by chewing insects by inducing both a general response to mechanical wounding and a specific response to herbivore-associated elicitors. In both cases, plant response involves complex biochemical and physiological changes. We compared chemical and physical responses of paper birch (B. papyrifera) and European white birch (B. pendula) stems to mechanical injury to determine if aspects of their wound response correspond with the much higher resistance of paper birch to bronze birch borer (Agrilus anxius). We also characterized stem responses to mechanical wounding plus bronze birch borer larval homogenate to determine if larval cues elicited a more specific response than mechanical wounding alone. In both species, wounding decreased concentrations of individual phenolics, total phenolics, and condensed tannins, perhaps because they were diverted to lignin biosynthesis, the concentration of which increased. Nitrogen concentration increased in both species while free amino acid concentrations declined, perhaps because they were utilized to synthesize proteins. Application of larval homogenate did not elicit a response different from that induced by mechanical injury. When comparing wound responses of the two birch species, phenolic profiles differed most conspicuously. However, multivariate analyses revealed no differences between constitutive and wound-induced phenolic profiles within each species, and the rate of wound periderm growth was equivalent between species. These results suggest that components of the wound response we measured may not contribute to interspecific variation in bronze birch borer resistance of paper birch and European white birch.