Interspecific plant competition mediates the metabolic and ecological signature of a plant-herbivore interaction under warming and elevated CO2

1. Biotic interactions shape community evolution, but we lack mechanistic insights on how metabolic and ecological processes under climate change are altered by biotic interactions. 2. We used a two-trophic model community consisting of the aphid Dysaphis plantaginea feeding on the forb Plantago lanceolata, and a grass competitor Lolium perenne that does not experience herbivory by the aphid. Monocultures and mixtures were exposed to the herbivory treatment and to three relevant simulated environmental changes as prevalent under current climate change (increased temperature, CO2, and increased temperature and CO2) 3. Elevated CO2 reduced the nitrogen content of P. lanceolata, while simultaneous increases of CO2 and temperature modified the plant metabolic component and the magnitude of these responses in different directions. Elevated CO2 enhanced defence systems in P. lanceolata, but these effects were not altered by warming. Interspecific plant competition did, however, neutralise the...