Understanding crop performance and pest control under climate change requires considering interactions among warming, elevated CO<sub>2</sub>, and trophic interactions.

Abstract

Investigating the combined effects of climate change and species interactions on species advances climate change research. However, such combined effects are understudied and may defy current hypotheses that focus on individual effects. We empirically examined how multiple environmental stressors (elevated temperature and CO₂) and trophic interactions (herbivory and predation) interactively affect crop performance and pest control in a tri-trophic agroecosystem including soybean (Glycine max), aphid (Aphis glycines), and ladybeetle (Coccinella septempunctata). Temperature (control/+2 °C/+4 °C), CO₂ (ambient/elevated), and trophic treatments (soybean/soybean-aphid/soybean-aphid-ladybeetle) were conducted in environmental chambers. Plant, herbivore, and predator traits (soybean nutrient content, defense, reproduction, and aphid and ladybeetle performance) were greatly influenced by interactions between abiotic (temperature, CO₂) and biotic (trophic) factors, often contradicting current hypotheses. For example, aphids reduced seed number; ladybeetles generally suppressed aphids and rescued seed production. However, this biocontrol was compromised under elevated temperature and CO₂, suggesting climate-induced changes in biocontrol effectiveness. We conclude: (1) To improve predictability, climate change research should include abiotic-biotic interactions as important mechanisms. (2) Empirical studies considering local climate-trophic interactions are critical for predicting regional food security. (3) While this study highlights species' plastic responses to climate change, experimental evolutionary studies will be needed to understand potential evolutionary adaptation.