© 2002 Heron Publishing—Victoria, Canada
Leaf chemical changes induced in Populus trichocarpa by enhanced UV-B radiation and concomitant effects on herbivory by Chrysomela scripta (Coleoptera: Chrysomelidae)
Jeffrey M. Warren (1), John H. Bassman (2, 3) and Sanford Eigenbrode (4)
1. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 2. Department of Natural Resource Sciences, Washington State University, Pullman, WA 99164-6410, USA / 3. Author to whom correspondence should be addressed (bassman@mail.wsu.edu) / 4. Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339, USA / Received October 24, 2001; accepted May 5, 2002; published online October 1, 2002
Summary
To assess the potential impact of enhanced ultraviolet-B (UV-B) radiation over two trophic levels, we monitored key leaf chemical
constituents and related changes in their concentration to dietary preference and performance of a specialist insect herbivore.
Ramets of Populus trichocarpa Torr. & Gray (black cottonwood) were subjected to near zero (0X), ambient (1X) or twice ambient (2X) doses of biologically
effective UV-B radiation (UV-BBE) in a randomized block design using either a square-wave (greenhouse) or a modulated (field) lamp system. After a 3-month
treatment period, apparent photosynthesis was determined in situ and plants were harvested for biomass determination. Leaf
subsamples were analyzed for nitrogen, sulfur, chlorophylls, UV-absorbing compounds and protein-precipitable tannins. Effects
of changes in these constituents on feeding by Chrysomela scripta Fab. (cottonwood leaf beetle) were determined by (1) adult feeding preference trials and (2) larval growth rate trials.
Enhanced UV-BBE radiation had minimal effects on photosynthesis, growth, leaf area and biomass distribution. In the greenhouse study, concentrations
of foliar nitrogen and chlorophylls increased, but tannins decreased slightly in young leaves exposed to enhanced UV-BBE radiation. There were no significant effects on these parameters in the field study. The concentration of methanol-extractable
foliar phenolics increased in plants grown with enhanced UV-BBE radiation in both the greenhouse and field studies. In feeding preference trials, adult C. scripta chose 2X-treated tissue almost twice as often as 1X-treated tissue in both greenhouse and field studies, but differences
were not statistically significant (P = 0.12). In the field study, first instar larvae grown to adult eclosion on 2X-treated leaves had a significant (P < 0.001) reduction in consumption efficiency compared with larvae grown on 1X-treated leaves. We conclude that effects of
enhanced UV-BBE radiation at the molecular-photochemical level can elicit significant responses at higher trophic levels that may ultimately
affect forest canopy structure, plant competitive interactions and ecosystem-level processes.
Keywords:
cottonwood, leaf beetle, plant–insect interactions, Salicaceae, ultraviolet radiation.
