Tl. Osier et Rl. Lindroth, Effects of genotype, nutrient availability, and defoliation on aspen phytochemistry and insect performance, J CHEM ECOL, 27(7), 2001, pp. 1289-1313
Genetic and environmental variability. and their interactions, influence ph
ytochemical composition and, in turn, herbivore performance. We evaluated t
he independent and interactive effects of plant genotype, nutrient availabi
lity, and defoliation on the foliar chemistry of quaking aspen (Populus tre
muloides) and consequences for performance of gypsy moths (Lymantria dispar
). Saplings of four genotypes were grown under two conditions of nutrient a
vailability and subjected to three levels of artificial defoliation. Concen
trations of all secondary and primary metabolites evaluated responded to at
least one or more of the experimental treatments. Of the secondary metabol
ites, phenolic glycosides were affected strongly by genotype, less so by nu
trient availability, and not induced by defoliation. Condensed tannins were
strongly dependent upon genotype, soil nutrient availability, and their in
teraction, and, in contrast to phenolic glycosides, were induced by artific
ial defoliation. Of the primary metabolites, foliar nitrogen was affected b
y genotype and soil nutrient availability. Starch concentrations were affec
ted by genotype, nutrient availability, defoliation and interactions among
these factors. Foliar water content responded to genotype, nutrient availab
ility, and defoliation, and the effect of nutrient availability depended on
genotype. Herbivore performance on these plants was strongly influenced by
plant genotype and soil nutrient availability, but much less so by defolia
tion. Although several of the compound types (condensed tannins, starch, an
d water) responded to defoliation, quantitative variation in these compound
s did not contribute to substantive changes in herbivore performance. Rathe
r, the primary source of variation in insect performance was due to plant g
enotype (phenolic glycoside levels), while nutrient availability (foliar ni
trogen levels) was of secondary importance, These results suggest that gene
tic variation in aspen plays a major role in determining patterns of insect
performance, whereas environmental variation, such as was tested, here is
of negligible importance.