PARENT SESSION
Poster Session #4: Herbivory.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Ecologically relevant chemistry is highly variable in a hybrid cottonwood system.

Rehill, Brian^*,1, Martinsen, Gregory², Schweitzer, Jennifer², Lindroth, Richard¹, Whitham, Thomas, ¹ University of Wisconsin, Madison, WI² Northern Arizona University, Flagstaff, AZ

ABSTRACT- Foliar nitrogen, condensed tannin, and phenolic glycoside contents affect herbivory and/or nutrient cycling. We measured these parameters in a hybrid cottonwood system of two parent species (Populus fremontii &Populus angustifolia), their F1 hybrids, and complex backcrosses to P. angustifolia (collectively called 'cross types'). We sampled at sites along the Weber River, UT, in May, June and August 2001, and collected leaves of different ontogenetic stages of each genet. Nitrogen contents were low among all cross types (mean = 2.2% dry weight) and declined throughout the growing season. Condensed tannins were highly variable among cross types but varied relatively little over the growing season. Most of the variation in condensed tannin contents was explained by cross type (66%), but genotype within cross type (16%) and the ontogenetic stage of leaves (6%) also accounted for significant amounts of variation (all: p < 0.0001). P. fremontii leaves had low tannin contents (% dry weight, mean ± SEM: 0.4 ± 0.1), F1 hybrids were intermediate (2.5 ± 2.4), and P. angustifolia leaves had higher contents (10.8 ± 3.6). Backcross hybrid leaves also had high tannin contents (16.3 ± 4.0). Phenolic glycoside contents (salicortin and an unidentified phenolic glycoside) were quite variable as well, with significant differences among cross types and ontogenetic stages.

KEY WORDS: genetics, ontogeny, hybridization, Populus