Elevated CO2 concentration affects the defense of tobacco and melon against lepidopteran larvae through the jasmonic acid signaling pathway.

The massive use of fossil fuels since the industrial revolution has led to a rapid increase in the concentration of carbon dioxide (CO₂) in the atmosphere. What effects elevated CO₂ concentrations (ECO₂) have on the defense mechanisms plants employ against insects remains poorly understood. This study showed that ECO₂ of 750 ± 20 mmol/mol, increased the photosynthetic rate and biomass gain of tobacco and melon plants. However, while mass gain of Spodoptera litura, a nocturnal moth in the Noctuidae family, was higher when feeding on tobacco plants under ECO₂, mass gain of Diaphania indica was reduced when feeding on melon plant at ECO₂ compared to ambient CO2. Plants have many mechanisms to defend themselves against insects. Jasmonic acid (JA) is a crucial element of plant defense against lepidopteran insects. Our study showed that JA levels increased in tobacco plants under ECO₂ but decreased in melon plants. It is speculated that ECO₂ changes plant resistance to insects mainly by affecting the JA signaling pathway. Nutrient analysis suggested defensive metabolites rather than changes in the total nitrogen or protein content of the plants led to the changes in plant defense levels under ECO₂. In summary, ECO₂ affects the interaction between plants and insects. The results may provide a theoretical basis for studying the changes in crop resistance to pests under ECO₂ and predicting the impact of ECO₂ on future agro-ecosystems.