Jolanta Rieksta:
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Insect feeding, i.e. herbivory, causes plant stress and damages vegetation. Plants can chemically defend themselves against herbivory, including by sending to the atmosphere increasing amounts of different mixtures of chemicals, plant volatiles. Plant volatiles are highly reactive and play an important role in biosphere-atmosphere interactions. With the ongoing climate change, we expect herbivory and insect outbreaks to increase in occurrence in arctic ecosystems.
However, few studies have quantified plant volatile responses to insect herbivory in natural populations in arctic ecosystems and even fewer studies have assessed how climatic changes that are predicted for arctic ecosystems, together with insect herbivory, affect volatile emissions from birch in the Arctic.
The main aim of this thesis was to increased our understand how increased insect herbivory pressure and the combined effects of insect herbivory and changing climate, such as warming and increased cloudiness, affect volatile emissions in arctic ecosystems.
The results showed that insect herbivory above background levels substantially increased volatile emissions from birch species in subarctic, and these responses were further modified by climate change. The results also showed that plant volatile responses to herbivory were highly variable and specific to species and study site. In some cases, plant volatile responses to herbivory were absent or the opposite of general expectations.
This thesis enhances our understanding and starts to fill the knowledge gap of how increased insect herbivore pressure and climate change affect VOC emissions from birch- dominated ecosystems. Furthermore, the work presented here shows the complexity of the relationships between insect herbivory and the effects of long-term climate treatments. The results suggest that insect herbivory is a significant driver of VOCs emitted during periods of active insect herbivore feeding and thus, should be accounted for when VOC emissions are scaled up from arctic ecosystems. The relationships between herbivory damage and VOC emissions found in this thesis can be used by modellers to separate the contributions of induced and constitutive emissions to the total VOCs emitted into the atmosphere and provide more input data for models from arctic ecosystems.