title: CO2and light effects on deciduous trees: growth, foliar chemistry, and insect performance.
abstract: This study examined the effects of CO2and light availability on sapling growth and foliar chemistry, and consequences for insect performance. Quaking aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), and sugar maple (Acer saccharum Marsh.) were grown in controlled environment greenhouses under ambient or elevated CO2(38.7 and 69.6 Pa), and low or high light availability (375 and 855 μmol m-2s-1). Because CO2and light are both required for carbon assimilation, the levels of these two resources are expected to have strong interactive effects on tree growth and secondary metabolism. Results from this study support that prediction, indicating that the relative effect of rising atmospheric CO2concentrations on the growth and secondary metabolism of deciduous trees may be dependent on light environment. Trees in ambient CO2-low light environments had substantial levels of phytochemicals despite low growth rates; the concept of basal secondary metabolism is proposed to explain allocation to secondary metabolites under growth-limiting conditions. Differences between CO2and light effects on the responses of growth and secondary metabolite levels suggest that relative allocation is not dependent solely on the amount of carbon assimilated. The relative growth rates and indices of feeding efficiency for gypsy moth (Lymantria dispar L.) larvae fed foliage from the experimental treatments showed no significant interactive effects of light and CO2, although some main effects and many host species interactions were significant. Gypsy moth performance was negatively correlated with CO2- and light-induced increases in the phenolic glycoside content of aspen foliage. Insects were not strongly affected, however, by treatment differences in the nutritional and secondary chemical components of birch and maple.
authors.affiliation: Department of Forest Ecology and Management, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA e-mail: mcdonald@entomology.wisc.edu Tel.: +1-715-3621110, , , , , , HM.
authors.forename: Evan P
authors.initials: EP
authors.lastname: McDonald
authors.affiliation: Department of Animal Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden, , , , , , SE.
authors.forename: Jep
authors.initials: J
authors.lastname: Agrell
authors.affiliation: Department of Entomology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA, , , , , , US.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lindroth
keywords: Key words CO2; Light; Phytochemistry; Plant-insect interactions; Tree growth