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

Abstract

Eucalypts are major emitters of biogenic volatile organic compounds (BVOCs), especially volatile isoprenoids. Emissions and incorporation of 13C 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°C to 45°C, and an increasing percentage of unlabelled carbon was incorporated into isoprene in heat‐stressed leaves. Intramolecular labelling 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 unlabelled monoterpenes, green leaf volatiles, methanol, and ethanol, indicating that the emission of stored volatiles was mainly induced by cellular damage. Emission of partially labelled acetaldehyde was also observed at very high temperatures, suggesting a double source of carbon, with a large unlabelled 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.

Source of 12C in Calvin–Benson cycle intermediates and isoprene emitted from plant leaves fed with 13CO2

“…It has been shown that labeling patterns in isoprene can vary. When eucalypts are heated from 30°C to 45°C, the proportion of unlabeled isoprene increases [43]. Similar results were shown with drought stress in poplar [44].…”

Isoprene: New insights into the control of emission and mediation of stress tolerance by gene expression

“…In comparison, monoterpenes are often stored in oil glands (often but not always within trichomes) or resin ducts, which means that their emission is sensitive to the effect of temperature on the vapour pressure of the monoterpene and on physical disruption of the enclosing structure. Stored monoterpenes do not become labelled when 13 CO 2 is fed to photosynthesizing leaves (Guidolotti et al, ).…”

Effects of elevated growth temperature and enhanced atmospheric vapour pressure deficit on needle and root terpenoid contents of two Douglas fir provenances

“…Besides their role in enhancing plants' tolerance at transient temperature increases, terpenoids seem to be involved in tolerance against long-term heat periods (Loreto et al, 1998;Sharkey and Singsaas, 1995). This is indirectly reflected by the general high abundance of stored terpenoids in plants of Mediterranean and (sub)-tropical ecosystems (Jardine et al, 2017;Fasbender et al, 2018;Guidolotti et al, 2019). Moreover, they also fulfil crucial functions against biotic stressors, as they provide defence against pathogens and herbivores (Zeneli et al, 2006;Martin et al, 2003;Gershenzon and Dudareva, 2007;Loreto et al, 2014).…”