Elevated atmospheric CO2 suppresses jasmonate and silicon-based defences without affecting herbivores

1. Elevated atmospheric CO2 (eCO2) not only increases plant growth but can also interfere with defence against insect herbivory through the disruption of the jasmonic acid (JA) pathway. Silicon (Si) plays an important role in plant stress tolerance and resistance to herbivory, particularly in grasses, many of which accumulate high amounts of Si. Activation of the JA pathway has been reported to stimulate Si uptake, while Si supplementation can alter both constitutive and induced phytohormone levels. A reduction in JA concentration under eCO2 has the potential to reduce Si uptake in plants. 2. Using both Si supplemented (Si+) and control (Si-) plants (Brachypodium distachyon) grown under ambient (400 ppm) and elevated (640 ppm) CO2 concentrations, we tested how plant growth, foliar Si concentration and endogenous JA responded to methyl jasmonate (MeJA) application and the subsequent effects on insect herbivore performance (Helicoverpa armigera). 3. Elevated CO2 reduced Si concentration b...