Effects of herbivore-induced nutrient stress on correlates of fitness and on nutrient resorption in scrub oak (Quercusilicifolia)

Abstract

We investigated effects of defoliation by gypsy moth (Lymantriadispar L.) larvae on plant fitness and on foliar nutrient dynamics in scrub oak (Quercusilicifolia Wangenh.). Complete defoliation of treatment plants in 1986 and 1987 resulted in the production of a second flush of leaves (secondary leaves) in each of those years. Insecticide effectively protected controls from herbivory. Mean radial stem growth in 1987–1988 and acorn production in 1988–1989 in plants defoliated by L. dispar were 49% and 88% less than in controls, respectively. Defoliation had little effect on the content of nitrogen, phosphorus, copper, manganese, and zinc in green leaves. However, there was significantly less nitrogen, copper, and zinc in senesced secondary leaves of treatment plants than in the primary leaves of controls. Reduced levels of copper and zinc were also evident in senesced primary leaves of defoliated plants in 1988, when no defoliation occurred. Resorption efficiencies for copper and zinc averaged, respectively, 29% and 117% higher in defoliated plants than in controls for all three years, supporting the hypothesis that resorption may be plastic in response to changes in the magnitude of internal nutrient pools. The lack of such a response in resorption of nitrogen and phosphorus may have been due to biochemical and (or) physiological limitations that prevented increased resorption, since resorption efficiencies of these elements were already high (72% and 75%, respectively).