Fertilizer quantity and type alter mycorrhizae-conferred growth and resistance to herbivores

1. Plants face a constant struggle to acquire nutrients and defend themselves against herbivores. Mycorrhizae are fungal mutualists that provide nutrients that can increase plant growth and alter resistance to herbivores. The beneficial effects of mycorrhizae for nutrient acquisition can depend on the quantity and type of soil nutrients available, with plants usually benefiting more in terms of growth from mycorrhizae when nutrients are limited. However, it is unclear how the addition of different nutrients might shift mycorrhizal conferred resistance to herbivores by changing defensive secondary chemistry and nutrient availability.

2. We conducted two concurrent greenhouse experiments to test how three levels of fertilizer (low, medium, and high) and three types of fertilizer (organic, organically derived, and inorganic) altered mycorrhizae-conferred resistance to herbivores in tomato plants. In addition, we looked at whether mycorrhizae-conferred resistance was driven by plant seco...