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Atmospheric Co-2 and Soil Water Availability: Consequences for Tree-Insect Interactions

Document Type

Article

Journal/Book Title/Conference

Canadian Journal of Forest Research

Volume

27

Issue

8

First Page

1281

Last Page

1290

Publication Date

1997

Abstract

The consequences of elevated CO2 for interactions between trees and associated insects will be influenced by the availability of other plant resources. We investigated the effects of CO2 and water availability on phytochemistry of quaking aspen (Populus tremuloides Michx.) and sugar maple (Acer saccharum Marsh.) and the associated performance of the forest tent caterpillar (Malacosoma disstria Hbn.). Seedlings were grown under ambient or elevated CO2 concentrations and under well-watered or drought conditions. We measured rates of gas exchange and subjected foliage to phytochemical assays. Bioassays were conducted to quantify larval performance on foliage from the various treatments. In general, elevated CO2 increased photosynthetic rates and had no effect on stomatal conductance, while drought reduced both parameters. Foliar nitrogen levels declined and secondary metabolite concentrations increased under enriched CO2, but starch and sugar levels were unaffected. All phytochemicals measured, with the exception of simple sugars, declined or did not change in response to drought. CO2- and drought-mediated changes in phytochemistry reduced forest tent caterpillar growth and food processing efficiencies, but the patterns were host-species specific. This work demonstrates that CO2 effects on forest trees will be mediated by the availability of water and that the direction and magnitude of responses will depend on the tree species involved, which will, in turn, affect patterns of host use by herbivorous insects.

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