Effects of nutrient availabiiity on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar
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Many studies have examined effects of nutrient availability on constitutive herbivore resistance of plants, but few have addressed effects on expression of rapid induced resistance (RIR). We quantified effects of two levels of nutrient availability on growth, biomass allocation, photosynthesis, and constitutive secondary metabolism of black poplar (>i>Populus nigra). We also examined effects of nutrient availability on expression of constitutive resistance of poplar to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), as well as RIR to both folivores in response to localized herbivory by gypsy moth. The high nutrient treatment had no effect on photosynthetic rate of poplar, but dramatically increased relative growth rate, total biomass, and total leaf area, while foliar phenolic concentrations and root:shoot ratio decreased. Plant growth was negatively correlated with foliar phenolic concentrations, which is consistent with predictions of the Growth/Differentiation Balance Hypothesis when increased nutrient availability increases growth without affecting photosynthesis. These responses of root:shoot ratio and constitutive secondary metabolism to nutrient availability are consistent with those proposed by models of adaptive phenotypic plasticity in resource allocation patterns. Nutrient availability affected constitutive resistance of poplar to first and fifth instar gypsy moth larvae, which grew much faster on high fertility plants. However, nutrient availability had no effect on constitutive resistance to whitemarked tussock moth. Localized herbivory elicited systemic RIR in poplar within 72 hours. However, the magnitude of RIR was dependent on nutrient availability, with differing effects on the two insect species. Expression of RIR to gypsy moth was most dramatic in the high fertility treatment. In contrast, RIR to whitemarked tussock moth was expressed only in the low fertility treatment. The idiosyncratic nature of effects of nutrient availability on constitutive and induced resistance challenges the value of using insect bioassays as surrogate measures of secondary metabolism for testing allocation models of plant defense, as well as the value of generaiized plant defense models for predicting effects of environmental variation on resistance to specific herbivores. These results also suggest that the effects of nutrient availability on the expression of RIR may represent a largely over-looked source of variation in plant/herbivore interactions.
Glynn, Carolyn; Herms, Daniel A.; Egawa, Marie; Hansen, Robert; Mattson, William J. 2003. Effects of nutrient availabiiity on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar. OIKOS 101(2):385-397