How the combinatorial stress of flooding, herbivory, and elevated carbon dioxide alter plant-insect interactions

In nature, plants encounter multiple stress factors, yet, to date our fundamental understanding of how they respond to combinatorial stress remains limited. Available studies reveal novel responses under combined stress factors, which cannot be discerned from each factor independently. Therefore, it is important to study responses to the various simultaneous abiotic and biotic factors encountered by plants under a changing climate, to build fundamental understanding of the mechanisms involved, and how they may interact. While there are many studies focusing on combinatorial stress responses—which reveal complex and numerous physiological, cellular, and molecular adaptations—knowledge of the dynamic response to simultaneous flooding, herbivory, and elevated carbon dioxide remains underexplored. This study aims to evaluate the interactive responses to this combinatorial stress by maize plants grown for 28 days in growth chambers, with elevated or ambient carbon dioxide, and infestation by Spodoptera frugiperda (Lepidoptera: Noctuidae). Plant tissue samples were collected after 25 days to determine reactive oxygen species, phytohormone concentrations, and non-structural total phenolic content. Headspace volatile organic compounds were collected using Gas Chromatography coupled with Mass Spectrometry. In addition, larval feeding assays were performed using diets of maize from each stress treatment combination. Results indicate that flooding alone increased maize total phenolic content, and volatile compound emissions. While S. frugipdera larvae on diets of flooded and combined stress treated maize decreased in growth performance. This suggests that maize experiencing extended periods of flooding or combined stress has reduced nutrient content and increased stress signaling compounds, which may inhibit feeding.