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 at elevated CO₂ while the Salicylic Acid (SA) pathway against piercing/sucking herbivores like aphids, is up-regulated in grains and legume crops. The objective of my study is to see whether chewing herbivore performance improves at elevated CO₂ (e-CO₂) and to see if vegetable crop resistance against them is reduced. As a preliminary test, I grew mutant lines of Arabidopsis thaliana plants defective in either the JA or SA pathway, and raised them at ambient (450 ppm) and e-CO₂ conditions (750 ppm) at the UBC Forestry plant growth room. I tested induced plant defense by pre-exposing them to cabbage looper feeding, and compared insect performance with that of non-induced plants at both CO₂ treatments. Results show that 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, I hope to predict pest damage in the future, and mitigate agricultural damage.