Impact of elevated temperature and ozone on the emission of volatile organic compounds and gas exchange of silver birch (Betula pendula Roth)

Abstract

Plants emit a considerable proportion of the carbon fixed by photosynthesis back into the atmosphere as volatile organic compounds (VOCs). Increasing evidence indicates that these compounds may have an important role in the adaptation of plants to changing climate, and that VOCs significantly influence atmospheric processes, such as formation of ozone (O3) and secondary organic aerosols. The effects of elevated temperature (ambient air temperature+0.8–1°C) and O3 (1.3–1.4× ambient O3), alone and in combination, on VOC emission, expression of genes related to VOC synthesis, and gas exchange were studied in four silver birch (Betula pendula Roth) clones grown in an open-air exposure field over two growing seasons. Photosynthesis and total emissions of mono-, homo- and sesquiterpenes and compounds other than terpenes [green leaf volatiles (GLVs)+methyl salicylate (MeSA)] were significantly increased and stomatal conductance decreased by temperature increase, while O3 reduced total emission of GLVs+MeSA and photosynthesis of birch. VOC emission rate corresponded with photosynthesis rate in the birch clones. Mono- and homoterpenes showed highest emission in August and GLVs+MeSA in July, whereas gas exchange decreased toward the end of the summer. In contrast to VOC emissions, transcription of genes encoding 1-deoxy-d-xylulose 5-phosphate synthase (DXS), 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) and isopentenyl diphosphate (IPP) isomerase at the initial stages of terpene synthesis pathway was lower at elevated temperature and higher at elevated O3. In conclusion, rising temperature will substantially increase VOC emissions from silver birch, presumably independently from stomatal conductance and partially as a consequence of increased availability of substrates due to enhanced photosynthesis.