Effects of Manual Damage on Turkey Oak (Fagales: Fagaceae) Foliar Tannin Concentration and Subsequent Herbivorous Insect Abundance

N. T. Lauer, A. M. Rossi

Abstract


Foliar tissue of turkey oak trees, Quercus laevis Walter (Fagales: Fagaceae), were manually damaged in an attempt to investigate their wounding response. Leaves were damaged with a hole punch early in the growing season to simulate herbivory. To another group of trees, the hormone, jasmonic acid, was applied to leaves in situ to determine if this volatile compound associated with wounding could elicit a defensive response in non-damaged trees. Foliar tannin concentration increased in both control and treated trees within 2 weeks after the experiment had been begun. Damaged trees exhibited a 56.5% increase in foliar tannin concentration and trees applied with jasmonic acid showed a 62.4% increase while control trees had only a 35.9% increase; however, these differences were not significant. Interestingly, manually damaged leaves demonstrated a 72.5% increase in crude tannin levels, whereas non-damaged leaves on damaged trees showed only a 42.3% increase. These differences approached significance and suggest that damage to leaves induced an increase in tannins, but this increase was not systemic. Moreover, damaged and jasmonate-treated trees had significantly fewer insects compared with control trees. Manually damaged leaves had the highest tannin concentration after treatment, and this was interpreted to be an induced defense or wounding response. Jasmonic acid appeared to have no effect on foliar tannin concentration; however, the number of herbivorous insects on jasmonic acid treated trees was similar to the number on damaged trees.

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