YARNES, CHRISTOPHER T* and WILLIAM J BOECKLEN. New Mexico State University, Department of Biology MSC 3AF, P.O. Box 30001, Las Cruces NM 88003. - Foliar chemistry variation in Quercus gambelii Nutt.: bottom-up cascade within a trophic system.
Spatio-temporal changes in Quercus gambelii Nutt. foliar chemistry
were measured along an elevation gradient. The carbon-nutrient balance
hypothesis predicts nutrient use and carbon allocation is determined
through balancing effects of competition and herbivory. Accordingly,
when nutrients are in ample supply, it is predicted competition should
favor carbon use primarily in growth. Conversely, within nutrient
stressed environments, change in carbohydrate status is expected to
increase carbon amounts allocated for defense. Competition pressure
varies with edaphic and ambient quality. Changes in topography
represent sharp local gradients of environmental heterogeneity that
can affect plant and insect populations and communities. Foliar
carbon/nitrogen ratios were measured across several elevations on
Mount Withington in the Cibola National Forest of west-central New
Mexico U.S.A.. Preliminary analyses indicate variation in leaf
chemistry with elevation. This variation produces a cascade of
bottom-up effects through which Q. gambelii foliar chemistry may
influence preference-performance in moths of the genus Phyllonorycter
(Lepidoptera: Gracilariidae), a Q. gambelii associated leaf-mining
herbivore. Larval performance is currently being investigated.
Key words: carbon nutrient balance hypothesis, cascade, chemistry, Quercus, trophic