Direct and indirect effects of elevated CO ₂ , warming and drought on plant–consumer interactions of <

Studying how global change factors influence plant‐consumer interactions (i.e. interactions with herbivores and pathogens) enables us to predict the future responses of plant communities to global change.

We aimed to determine the direct and indirect effects of global change on plant‐consumer interactions of Plantago lanceolata (ribwort plantain). In experimental grassland plots exposed for 10 years to elevated CO ₂ concentrations (+300 ppm), warming (+3°C), drought and their combinations, we measured leaf traits of P. lanceolata , including leaf dry matter content, specific leaf area, carbon‐to‐nitrogen ratio, leaf toughness, phenol concentration and the concentrations of other secondary metabolites. We quantified field consumption damage as the % leaf area affected, distinguishing between types of herbivore and pathogen damage. A laboratory pairwise choice experiment examined the feeding preferences of Locusta migratoria (migratory locust) for leaves sampled from the different global change treatments.

Elevated CO ₂ , warming and drought affected plant‐consumer interactions of P. lanceolata both directly and indirectly, the latter being mediated by shifts in plant traits. For instance, warming directly favoured powdery mildew infection and sucking damage, and indirectly increased sucking damage by reducing the concentration of a flavonoid glycoside. Plant traits were not influenced by interactions between global change factors, but consumption damage was—warming increased sucking damage under ambient precipitation but not under drought, and elevated CO ₂ decreased chewing damage under ambient temperature but not under warming.

Synthesis : Warming, elevated CO ₂ , drought and their interactions had direct and indirect (plant‐trait‐mediated) effects on field plant consumption and feeding preferences of the locust L. migratoria . The effects, however, largely differed between different consumption types, despite all being studied on the same species in the same system, highlighting the complexity of these interactions. Future studies should thus avoid excessive generalizations and attempt to study a broad range of plant traits and consumers under realistic, multifactorial global change conditions.