The impact of elevated CO₂ on plant defense and plant-insect interactions

Over the past few decades, CO2 has been rising rapidly. High levels of CO2 can potentially change metabolic processes in plant tissue and influence their interactions with other organisms. Previous studies have shown that elevated CO2 alters nutrient balance and affects plant defense against different types of herbivores. In general, the jasmonic acid pathway (JA) for defense against chewing herbivores like caterpillars, is inhibited while the salicylic acid (SA) pathway against piercing/sucking herbivores like aphids, is up-regulated in grains and legume crops at elevated CO2. The objective of this study is to see whether chewing herbivore performance improves on vegetable crops at elevated CO2 (e-CO2) and to see if vegetable crop resistance against them is reduced. As a preliminary test, Arabidopsis thaliana plants were raised at ambient (450 ppm) and e-CO2 conditions (750 ppm). Plant defenses were induced by pre-exposing them to cabbage looper feeding, and insect performance on these plants was compared with that of non-induced plants at both CO2 treatments. Results show that defense induction significantly reduced cabbage looper growth at ambient CO2, but was much less effective at e-CO2. By continuing this research with commercial vegetable crops such as the tomato, risks in crop-pest interactions that are associated with climate change can be assessed, and the data can be used to improve current pest management programs.