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Theses

Les effets du changement climatique sur les émissions volatiles des grandes cultures et forêts du Sud de la France

Abstract : Since the twentieth century, the mean temperature and atmospheric concentration of CO2 have been constantly increasing and climate models suggest even greater future increases. The modification of climatic factors impacts Volatile Organic Compounds (VOCs) emitted by terrestrial vegetation. These compounds are essential for plants’ interactions with their biotic and abiotic environment and are involved in multiple chemical reactions in the atmosphere since they modify the concentrations of greenhouse gases and participate in the formation of secondary organic aerosols. The degree of involvement of VOCs in climate change and the importance of its feedback on volatile emissions need to be clarified. Isoprenoids (isoprene, monoterpenes and sesquiterpenes) are the most emitted VOCs by terrestrial vegetation and the most reactive species in the atmosphere. The individual and combined effects of temperature and CO2 concentration are relatively well known on isoprene emissions, but it remains unclear for monoterpenes and sesquiterpenes: the emission of these compounds can vary according to the presence or the absence of storage structures in the plant and can be modified by the induction of biotic stress.The main aim of this thesis was therefore to clarify the short-term and long-term effects of an increase in temperature and CO2 concentration on the VOCs emitted by 3 plants typical of agroecosystems in the south of France and whose emission strategies differ: sweet wormwood (Artemisia annua), a strong emitter of constituent VOCs stored in glandular trichomes, holm oak (Quercus ilex), a strong emitter of novo-synthesized constituent VOCs and maize (Zea mays) strong emitter of VOCs induced by biotic stress. The plants were grown in air-conditioned greenhouses under 4 different climatic scenarios: 2 temperature regimes (25 - 30 °C) were associated with 2 CO2 concentrations (400 - 800 ppm) in a 2x2 factorial plan. VOC emissions from plants in different greenhouses were then measured under different assay conditions according to the same design to separate the short- and long-term effects of the 2 parameters. Secondly, we looked at the variability of VOC emissions within the same species, maize. The emissions of 21 maize genotypes were quantified before and after the exogenous application of methyl jasmonate (MeJA), a plant hormone simulating biotic stress.The results of these experiments show that overall the short-term increase in temperature increases volatile emissions, the increase in CO2 concentration decreases them, and that the increase in the two parameters increases them. There is however an effect of the presence of storage structures on the response to CO2 and of the category of VOCs on the response of emissions to temperature. The long-term impact of climate parameters on emissions is more vague: no effect of growth under elevated temperature was found on emissions, a negative effect of growth under elevated CO2 was found on VOCs emitted by Artemisia annua, and the growth under elevated temperature and elevated CO2 does not modify the total quantity but modifies the proportions of VOCs induced in Zea mays. The study of intraspecies variability has shown that there are qualitative and quantitative differences between the emissions of maize genotypes and that the amplitude of response of emissions to biotic stress depends on the genotype. Overall, MeJA induced the synthesis and release of new VOCs and increased the amount of VOCs emitted. These results provide new information on the possible repercussions of the choice of variety on the atmospheric load of VOCs in agroecosystems and suggest that the quantity and quality of VOCs emitted in response to climate change are dependent on the species but also on possible biotic stress.
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Juliane Daussy. Les effets du changement climatique sur les émissions volatiles des grandes cultures et forêts du Sud de la France. Sciences agricoles. Université Montpellier, 2020. Français. ⟨NNT : 2020MONTG010⟩. ⟨tel-03136981⟩

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