Item

Abstract

Tree saplings in temperate forests world-wide experience intense browsing from deer and
other mammalian herbivores. However, when compared to insect herbivory, our knowledge
about the cues that trigger mammalian-induced defence responses in trees is limited.
2. We studied responses of field-grown saplings of European beech (Fagus sylvatica L.) and
Sycamore maple (Acer pseudoplatanus L.) to simulated browsing by (i) clipping apical buds or
leaves and (ii) additionally applying roe deer (Capreolus capreolus L.) saliva to the cut surface.
We analysed induced changes in phytohormones and phenolics in the saplings’ remaining buds
or leaves, respectively.
3. In both species, jasmonates were activated after clipping of buds and leaves. Importantly,
additional saliva application activated salicylic acid in beech leaves and led to increases in cytokinins
in beech buds. Saliva application also led to an increased biosynthesis of several hydrolysable
tannins (mainly ellagitannins) and flavonols in maple leaves. Condensed tannins, the
most abundant phenolics in beech buds and leaves, did not change after either clipping or
saliva application. However, clipping with additional saliva application decreased levels of
phenolic acids (cinnamic acid derivatives) in beech buds.
4. We conclude that the two tree species perceive and respond to unknown elicitors in the deer
saliva, resulting in changes in phytohormone levels and defence-associated secondary metabolites.
5. We suggest that variation in induced defence responses between tree species as well as
between buds and leaves is related to differences in morphological traits, which interrelate with
chemical traits and result in species-specific strategies to respond to mammalian herbivory.