Pe. Hatcher et al., THE EFFECT OF NITROGEN-FERTILIZATION AND RUST FUNGUS INFECTION, SINGLY AND COMBINED, ON THE LEAF CHEMICAL-COMPOSITION OF RUMEX OBTUSIFOLIUS, Functional ecology, 11(5), 1997, pp. 545-553
1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusif
olius growing in a range of nutrient conditions and also on plants inf
ected with the foliar fungus Uromyces rumicis. In a controlled environ
ment, we investigated the effect of fertilizing plants with eight nitr
ate and four ammonium concentrations, with or without infection, on le
af nutritional quality. 2. Increasing nitrate fertilization increased
leaf oxalate, total nitrogen and nitrate concentrations and water cont
ent, and decreased total non-structural carbohydrate (NSC) concentrati
ons. Increasing ammonium fertilization increased leaf nitrogen concent
ration and water content, decreased nitrate and NSC concentrations, an
d had no effect on oxalate concentrations. 3. Infection produced a mai
nly additive effect to fertilization, increasing NSC and oxalate, and
decreasing nitrate and nitrogen concentration in whole plants fed nitr
ate, and increasing nitrate and NSC in whole plants fed ammonium. 4. Y
oung leaves on infected plants remained uninfected and had greater nit
rogen and NSC concentrations, and lower oxalate and nitrate concentrat
ions, than infected leaves on the same plant. 5. These results are dis
cussed in relation to changes in C:N and NSC:organic nitrogen ratios,
the effect of nitrate and oxalate, and the known feeding and ovipositi
on preferences of the beetle. The results suggest that there is an opt
imum nitrogen fertilization level for G. viridula development.