Abstract:

Atmospheric CO₂ levels are rapidly increasing due to human activities. However, the effects of elevated CO₂ (ECO₂) on plant defense against insects and the underlying mechanisms remain poorly understood. Here we show that ECO₂ increased the photosynthetic rates and the biomass of tobacco and rice plants, and the chewing lepidopteran insects Spodoptera litura and Mythimna separata gained less and more mass on tobacco and rice plants, respectively. Consistently, under ECO₂, the levels of jasmonic acid (JA), the main phytohormone controlling plant defense against these lepidopteran insects, as well as the main defense‐related metabolites, were increased and decreased in insect‐damaged tobacco and rice plants. Importantly, bioassays and quantification of defense‐related metabolites in tobacco and rice silenced in JA biosynthesis and perception indicate that ECO₂ changes plant resistance mainly by affecting the JA pathway. We further demonstrate that the defensive metabolites, but not total N or protein, are the main factors contributing to the altered defense levels under ECO₂. This study illustrates that ECO₂ changes the interplay between plants and insects, and we propose that crops should be studied for their resistance to the major pests under ECO₂ to predict the impact of ECO₂ on future agroecosystems.