Effects of elevated CO2 on plant-insect interactions

Project lead: Jimmy (Kyu Baik) Ha

PIEE Lab members involved: Warren Wong, Dennis Chiu, Savi Raghuraman

Recently, CO2 has been rising rapidly due to human activity. Other than its greenhouse effect, CO2 influences many factors, one of which is plant biochemistry. High CO2 can change metabolic processes in plant tissue and influence their interactions with other organisms. Previous studies showed that elevated CO2 alters plant defense against insect herbivores. In general, the jasmonic acid pathway (JA) for defense against chewing herbivores was downregulated in grains and legume crops at elevated CO2. However, there are still knowledge gaps for vegetable and fruit crops, which are essential for agriculture. This study aims to see whether chewing herbivore performance improves on vegetable crops at elevated CO2 (e-CO2) as a result of reduced JA defenses. As a preliminary test, Arabidopsis thaliana plants were raised at ambient (450 ppm) and e-CO2 conditions (750 ppm). Afterwards, cabbage looper performance on those plants was compared. Results showed that defense induction was significantly less effective at e-CO2. By continuing this research with 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.

For the main experiment, two groups of tomato plants will be grown under ambient (450 ppm) or elevated (750 ppm) CO2 conditions. These plants will then be exposed to herbivory from both generalist and specialist herbivores such as the cabbage looper (generalist) and tobacco hornworm (specialist), and both plant and insect performance will be investigated. The main hypothesis remains the same: plant hormonal defenses like the JA pathway may be downregulated under e-CO2 in vegetable crops, similar to that in legumes and grains. The amount of defensive compounds will be measured and compared between those plants with a focus on JA-regulated products, using methods such as metabolite profiling and transcriptomic analyses. Insect responses will be measured by looking at the weight of the caterpillars that feed on them, as well as the strength of attraction of insect predators to injured plants. In the face of rapid changes in atmospheric CO2, knowledge is key, and by investigating how tomato defenses are affected and potentially weakened at high CO2 conditions, it becomes possible to formulate strategies for damage mitigation. 

Key words: Elevated CO2, tomato, plant defenses, jasmonic acid, cabbage looper, tobacco hornworm