Leaf chemical changes induced in Populus trichocarpa by enhanced UV-B radiation and concomitant effects on herbivory by Chrysomela scripta (Coleoptera: Chrysomelidae)

Abstract

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-B(BE)) 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-B(BE) 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-B(BE) 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-B(BE) 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-B(BE) 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.

UV-B effects on the nutritional chemistry of plants and the responses of a mammalian herbivore

“…In turn, these changes had little to no effect on the predicted and actual digestibility and preference of a forb and shrub consumed by a small ruminant, the blue duiker. Our results differ in several ways to those of previous studies on the effects of UV-B radiation on plants (Ambasht and Agrawal 2003;de la Rosa et al 2001;Schnitzler et al 1997;Warren et al 2003) and studies documenting the effects of changes in plant chemistry caused by UV-B radiation in invertebrates (McCloud and Berenbaum 1999;Veteli et al 2003;Warren et al 2002). First, in many plants cell-wall components, such as fiber and lignin, respond to light intensity (Blair et al 1983).…”

“…The nutritional quality of food, in turn, can drive production, movements, and population dynamics (Cook et al 2004) of economically and ecologically important wild and domestic ruminants. Although recent studies have indicated that insects are affected by chemical changes induced by enhanced UV-B radiation (McCloud and Berenbaum 1999;Veteli et al 2003;Warren et al 2002), responses of mammalian herbivores to changes in food chemistry induced by enhanced UV-B radiation have rarely been studied. However, some evidence suggests that when plants have been naturally or experimentally excluded from UV-B radiation, they may be more nutritious for herbivores.…”

Long-term acclimation of mesophyll conductance, carbon isotope discrimination and growth in two contrasting Picea asperata populations exposed to drought and enhanced UV-B radiation for three years

“…Nevertheless, we are aware the conclusions about the effect of drought stress and its interaction with UV-B radiation exposure can be put in perspective of a greenhouse situation only, as the limitations of our controlled environmental studies are recognized. In our study, on-off lamp procedure for providing UV-B irradiation has been known to produce higher daily and seasonal UV doses than expected because there is no compensation (lamp modulation) for any reduction in incoming solar radiation during overcast and cloudy conditions, and during morning and afternoon periods (see Sullivan et al, 1994;Warren et al, 2002). Consequently, this is likely to exaggerate the UV-B response.…”

The Wound-, Pathogen-, and Ultraviolet B-ResponsiveMYB134Gene Encodes an R2R3 MYB Transcription Factor That Regulates Proanthocyanidin Synthesis in Poplar

“…The activation of flavonol biosynthetic genes exhibited a reduction at 12 h, which may have been caused by the absence of the stimulus during the night or by circadian regulation. Flavonol glycosides are known to be important UV-B protective compounds (Li et al, 1993;Landry et al, 1995), and increased flavonol accumulation in leaves has been observed in poplar and other trees under elevated UV-B light (Warren et al, 2002(Warren et al, , 2003Keski-Saari et al, 2005;Turtola et al, 2005). HPLC analysis of extracts from leaves after 7 d of HL exposure revealed a large increase in total flavonol glycosides ( Fig.…”