Pulsed drought: The effects of varying water stress on plant physiology and predicting herbivore response

Climate change is predicted to increase the frequency of drought conditions and alter plant-insect interactions. Despite over 530 studies on the effects of water-deficit stress on plant-insect interactions, we still cannot accurately predict plant-insect interactions under drought conditions. Most studies have focused on how insect herbivores respond to water-deficit-stressed plants, with little attention on how stressed plants and changes in plant physiology may contribute to the variation in herbivore response. Variation in herbivore response to water-deficit-stressed plants may be due to stress-induced changes in plants and how these changes differ with stress severity. In this study, we determined the effects of water-deficit stress on cotton (Delta Pine 174RF) physiology in an agroecosystem using pulsed moderate and severe stress. Our goal was to determine how moderate and severe water-deficit stress affect cotton (Gossypium hirsutum L.) physiology differently in terms of photosynthesis, development, water use, and nutrient content. We found that moderate and severely stressed plants had many different physiological responses that may contribute to the variation we see in herbivore response to stressed plants. For instance, moderately stressed plants were more vigorous and more developed than severely stressed plants, whereas severely stressed plants had more amino acids than moderately stressed plants. We predict that insect herbivores feeding on moderately and severely stressed plants would encounter differences in C assimilation, water content (stomatal conductance, transpiration), chlorophyll content, and concentrations of amino acids and digestible carbohydrates. It is clear that field studies should consider how differences in stress severity can affect plant-insect interactions.