Soil degradation slows growth and inhibits jasmonate-induced resistance in Artemisia vulgaris

German reunification closed factories that produced point-source emissions and, in so doing, provided ecologists with well-de-fined pollution gradients with which to study the effects of plant stress on induced resistance against herbivores. We characterized a gradient of severely degraded soil from the dust emissions of a former fertilizer factory and selected three sites along this gradient to study the interaction of pollution stress and herbivore resistance in a single maternal lineage of Artemisia vulgaris that had colonized these disturbed habitats. We measured A. vulgaris growth, reproductive success, and inducible herbivore resistance by eliciting plants at each site with a quantitative methyl jasmonate (MeJA) treatment, and measured the reproductive success of two native herbivores, the aphid Macrosiphoniella artemisiae (in the field) and the grasshopper Chorthippus rhollis (in the laboratory). Soil heavy metals and phosphate contents decreased with distance from the former factory, while cation exchange capacity and nitrogen content, as well as A. vulgaris growth and seed germination (measured in both field and laboratory assays) increased, demonstrating a plant stress that is mediated by soil degradation. MeJA elicitation decreased A. vulgaris growth and seed production and the reproductive success of the two insect herbivores. MeJA-induced herbivore resistance waned in plants grown on degraded soils and was correlated with changes in concentrations of leaf secondary metabolites of which chlorogenic acid, which increased dramatically in MeJA-induced plants grown on moderately degraded soil but not in plants from heavily degraded soil, was representative. We conclude that herbivore-induced resistance is constrained in slow-growing plants on degraded soils and that the jasmonate cascade likely mediates plant responses to both types of environmental stresses. A central role for the jasmonate cascade in mediating plant responses to both abiotic and biotic stresses provides a mechanistic understanding of the plant vigor hypothesis.