Emission of constitutive isoprene, induced monoterpenes and other volatiles under high temperatures in Eucalyptus camaldulensis: a 13 C labelling study.

Eucalypts are major emitters of biogenic volatile organic compounds (BVOCs), especially volatile isoprenoids. Emissions and incorporation of 13 C in BVOCs were measured in Eucalyptus camaldulensis branches exposed to rapid heat stress or progressive temperature increases, in order to detect both metabolic processes and their dynamics. Isoprene emission increased and photosynthesis decreased with temperatures rising from 30 up to 45 °C, and an increasing percentage of unlabeled carbon was incorporated into isoprene in heat-stressed leaves. Intramolecular labeling was also incomplete in isoprene emitted by heat-stressed leaves, suggesting increasing contribution of respiratory (and possibly also photorespiratory) carbon. At temperature above 45 °C, a drop of isoprene emission was mirrored by the appearance of unlabeled monoterpenes, green leaf volatiles, methanol, and ethanol, indicating that the emission of stored volatiles was mainly induced by cellular damage. Emission of partially labeled acetaldehyde was also observed at very high temperatures, suggesting a double source of carbon, with a large unlabeled component likely transported from roots and associated to the surge of transpiration at very high temperatures. Eucalypt plantations cover large areas worldwide, and our findings may dramatically change forecast and modelling of future BVOC emissions at planetary level, especially considering climate warming and frequent heat waves.