THE ECOLOGICAL SIGNIFICANCE OF NICKEL HYPERACCUMULATION - A PLANT-CHEMICAL DEFENSE

Nickel hyperaccumulating plants have more than 1000 mg Ni kg(-1) dry weight when grown on nickel-bearing soils. We hypothesized that Ni hyperaccumulation could serve as a chemical defense against herbivores. In feeding experiments with potential insect herbivores and Ni hyperaccumulating plants, only those insects fed leaves from plants grown on non-nickel-bearing soil survived or showed a weight gain. Among chemical parameters measured, only Ni content of plants was sufficient to explain this result. When subjected to herbivory by lepidopteran larvae, plants grown on Ni-amended soil showed greater survival and yield than plants on unamended soil. Ni hyperaccumulation may be an effective plant chemical defense against herbivores because of its high lethality, apparent low cost, and broad spectrum of toxicity.