Climate warming and plant biomechanical defences: silicon addition contributes to herbivore suppression in a pasture grass

1. Plants, notably the Poacae, often accumulate large amounts of silicon (Si) from the soil. Si has multiple functional roles, particularly for alleviating abiotic and biotic stresses (e.g. defence against herbivores). Recent evidence suggests that environmental change, including temperature changes, can diminish Si accumulation which could affect functions such as herbivore defence. 2. Using a field warming experiment, we grew a pasture grass (Phalaris aquatica) that was either supplemented or untreated with Si (+Si and -Si, respectively) under ambient and elevated (+2.8ºC above ambient) air temperatures. We quantified soil water, plant growth rates, Si accumulation, leaf biomechanical properties and in situ relative growth rates of a herbivorous global insect pest (Helicoverpa armigera). 3. Si supplementation promoted shoot and root biomass by c. 48% and 61%, respectively under ambient temperatures, but these gains were not apparent under warmed conditions. 4. Warmer temperatures redu...