Impacts of Climate Change, Extreme Events, and Biotic Stress on Plant CO₂ Exchange and Volatile Organic Compound Emissions: Experimental Evidence and Modelling Advances

Place

Building: Universitetsparken 15, DK-2100 Copenhagen, Building 1, Auditorium A

Abstract

Global temperatures are rising, with Arctic regions warming particularly fast. At the same time, the frequency and intensity of environmental stressors such as heat waves, drought, and insect herbivory are increasing. These changes can affect plant CO₂ exchange and the emission of volatile organic compounds (VOCs)—a diverse group of plant secondary metabolites that evaporate readily and have important implications for atmospheric chemistry and the climate. This thesis quantifies how warming, heat waves, drought, and insect herbivory affect plant CO₂ exchange and VOC emissions in tundra shrubs and subalpine forests. The results show that warming and associated stress events can substantially alter both plant net CO₂ uptake and VOC emissions. Importantly, warming modifies plant responses to additional stressors in ways that cannot be predicted from the effects of individual drivers alone, highlighting the importance of non-additive interactions among climate change factors. In many cases, warming amplified VOC emission responses to heat waves and herbivory, resulting in increased emissions of isoprene, acetaldehyde, methanol, and monoterpenes. Furthermore, warming may offset the negative effects of herbivory on photosynthetic CO₂ uptake. These findings provide new insights into how multiple climate change related drivers interact to influence plant physiological processes. By integrating measurements of both CO₂ exchange and VOC emission responses to multiple drivers, and including sequential and compound stressors, this thesis contributes to a more comprehensive understanding of plant responses to environmental change, providing essential information for improving the representation of plant gas exchange in ecosystem models.