PARENT SESSION
Contributed Oral Session 102: Herbivory: Effects of Photosynthesis; Nutrients
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal

Plant-mediated response of Trichoplusia ni performance to elevated CO₂ and increased N availability.

Sudderth, Erika^*,1, Holbrook, N.¹, ¹ Harvard University, Cambridge, MA

ABSTRACT- Global change will directly influence plant and insect physiology, leading to indirect effects on the interactions between plant species and their insect herbivores. Extensive research has led to a range of detailed predictions regarding leaf chewing insect herbivore response to single global change factors. However, the responses of plant-insect interactions to simultaneous change in multiple environmental factors are less well understood. We investigated how the performance of a generalist insect herbivore (Trichoplusia ni) is affected by the physiological response of host plants to elevated CO₂ and high N. We compared caterpillar performance on host plants that utilize different photosynthetic physiologies, Amaranthus viridis (C₄) and Polygonum persicaria (C₃). Plants were grown under a factorial combination of ambient (400 ppm) or elevated (800 ppm) CO₂ conditions, and low (25 ppm) or high (75 ppm) N concentrations. T. ni caterpillars performed significantly better on A. viridis (C₄) compared to P. persicaria (C₃), gaining over twice as much biomass during the ten day feeding period. High N increased caterpillar performance on both plant species, while elevated CO₂ reduced the performance of caterpillars feeding on the C₃ plant (P. persicaria). High N increased maximum photosynthesis rates, above ground biomass, and leaf area of both A. viridis and P. persicaria. P. persicaria showed larger growth responses to elevated CO₂ than A. viridis, likely leading to greater changes in leaf characteristics which affected T. ni performance. The only significant CO₂ by N interactions were seen for biomass and leaf area responses of P. persicaria, but these plant responses did not lead to a corresponding CO₂ by N interaction affecting caterpillar performance. These results imply that although CO₂ by N interactions are commonly observed for plant responses, elevated CO₂ and increased N availability may not interact to affect insect herbivore performance.

Key words: Global Change, C₃ vs C₄, Trichoplusia ni, Elevated CO₂