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Effects of CO 2 and light on tree phytochemistry and insect performance
Author(s) -
Agrell Jep,
McDonald Evan P.,
Lindroth Richard L.
Publication year - 2000
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1034/j.1600-0706.2000.880204.x
Subject(s) - sugar , botany , deciduous , biology , light intensity , horticulture , phytochemistry , population , aceraceae , maple , food science , physics , demography , sociology , optics
Direct and interactive effects of CO 2 and light on tree phytochemistry and insect fitness parameters were examined through experimental manipulations of plant growth conditions and performance of insect bioassays. Three species of deciduous trees (quaking aspen, Populus tremuloides ; paper birch, Betula papyrifera ; sugar maple, Acer saccharum ) were grown under ambient (387±8 μL/L) and elevated (696±2 μL/L) levels of atmospheric CO 2 , with low and high light availability (375 and 855 μmol×m −2 ×s −1 at solar noon). Effects on the population and individual performance of a generalist phytophagous insect, the white‐marked tussock moth ( Orgyia leucostigma ) were evaluated. Caterpillars were reared on experimental trees for the duration of the larval stage, and complementary short‐term (fourth instar) feeding trials were conducted with insects fed detached leaves.
Phytochemical analyses demonstrated strong effects of both CO 2 and light on all foliar nutritional variables (water, starch and nitrogen). For all species, enriched CO 2 decreased water content and increased starch content, especially under high light conditions. High CO 2 availability reduced levels of foliar nitrogen, but effects were species specific and most pronounced for high light aspen and birch. Analyses of secondary plant compounds revealed that levels of phenolic glycosides (salicortin and tremulacin) in aspen and condensed tannins in birch and maple were positively influenced by levels of both CO 2 and light. In contrast, levels of condensed tannins in aspen were primarily affected by light, whereas levels of ellagitannins and gallotannins in maple responded to light and CO 2 , respectively.
The long‐term bioassays showed strong treatment effects on survival, development time, and pupal mass. In general, CO 2 effects were pronounced in high light and decreased along the gradient aspen birch maple. For larvae reared on high light aspen, enriched CO 2 resulted in 62% fewer survivors, with increased development time, and reduced pupal mass. For maple‐fed insects, elevated CO 2 levels had negative effects on survival and pupal mass in low light. For birch, the only negative CO 2 effects were observed in high light, where female larvae showed prolonged development. Fourth instar feeding trials demonstrated that low food conversion efficiency reduced insect performance. Elevated levels of CO 2 significantly reduced total consumption, especially by insects on high light aspen and low light maple.
This research demonstrates that effects of CO 2 on phytochemistry and insect performance can be strongly light‐dependent, and that plant responses to these two environmental variables differ among species. Overall, increased CO 2 availability appeared to increase the defensive capacity of early‐successional species primarily under high light conditions, and of late‐successional species under low light conditions. Due to the interactive effects of tree species, light, CO 2 , and herbivory, community composition of forests may change in the future.