Interactions between temperature, intercellular CO 2 concentration, light and a unifying conceptual model response in controlling leaf isoprene emission rates

• Ano de defesa: 2017
• Autor(a) principal: Souza, Vinícius Fernandes de
• Orientador(a): Gonçalves, José Francisco de Carvalho
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Instituto Nacional de Pesquisas da Amazônia – INPA
• Programa de Pós-Graduação: Ciências de Florestas Tropicais - CFT
• Palavras-chave em Português: Amazônia; Espécies arbóreas; Fotossíntese
• Link de acesso: https://repositorio.inpa.gov.br/handle/1/4991; http://lattes.cnpq.br/8057265149242009

Isoprene is an unsaturated and volatile hydrocarbon (formula C 5 H 8 ) more emitted by vegetation, with emphasis on tree species. This molecule plays a significant role in the modulation of the atmospheric composition besides conferring adaptive advantage to the emitting plants against biotic and abiotic stress. Biogenic emissions of isoprene are controlled by temperature, irradiance and CO 2 concentration ([CO 2 ]). Given the increase in temperature and [CO2], it is of crucial importance to develop more precise models of isoprene emission as regards their insertion in the process of global climate change. In this study, the main evidence of the origin and the different carbon sources that contribute to the synthesis of isoprene were reviewed from periodic high impact factor (Chapter 1). Supported and updated on the theme of the synthesis and emission of isoprene, experiments were conceived and carried out with the objective of investigating the prediction of emission rates. Establishing a comparison of the models obtained “in silico” with two other models well known in the literature (Chapter 2) and, finally, an experiment was conducted in order to examine the interactive effects of temperature and [CO 2 ] on the rates of emission of isoprene in two species: Inga edulis (a species of tropical climate) and Populus tremula (a species of temperate climate) (Chapter 3). In addition, we quantitatively represent the effect of different environmental conditions on the fraction of electrons allocated for carbon assimilation and for the synthesis of isoprene. The increase in temperature may counterbalance the suppression effect of high [CO 2 ] on the emission rates of isoprene and the extent of the combined effects of temperature and [CO 2 ] may be associated with the sensitivity of the photosynthetic mechanisms coupled to energy absorption and carbon assimilation between the species. In P. tremula, the CO 2 suppression effect decreased as temperature increased and disappeared under elevated temperatures as a result of the acceleration of isoprene synthase activity (EC 4.2.3.27 ). The reduction of net photosynthetic rates, V cmax , ETR e F v’ /F m’ in function to temperature led to a decrease in the concentration of dimethylallyl diphosphate (DMADP) above 35oC. The higher vulnerability of the photosynthetic processes will contribute to the greater electron supplementation in the isoprene synthesis, which reflected in a great loss of photosynthetic carbon as isoprene. In general, elevated [CO 2 ] attenuated the effect of temperature on photosynthesis in particular on the fluorescence parameters which contributed to the increase in DMADP pools. For tropical species, the positive effect of temperature on isoprene synthase activity did not reduce the inhibitory effect of high CO 2 . The suppression of viiiisoprene emission rates was related to changes in the availability of DMADP rather than changes in isoprene synthase activity per se. The best fit of the photosynthetic processes for high temperature contributed to the greater influx of electrons to the reactions in the Calvin- Benson cycle to support the higher carboxylation rates. In addition, from the A/C i curve was observed decrease in net photosynthesis and ETR under intercellular CO 2 concentration, suggesting a possible link between ATP limitation and changes in carbon partitioning with declining isoprene emissions. The model (energetic status model– Morfopoulos et al. 2014) was able to reproduce changes in the isoprene emission rates induced by changes in [CO 2 ] and irradiance. A trend to increase the isoprene/photosynthesis ratio was observed with increasing irradiance. In addition, the electron flow for photorespiration, photorespiration rate, parallel isoprene emission rates under all parallelized the emission rates of isoprene under all conditions studied. Our observations suggest that difference in the tolerance threshold between species for temperature increase may determine the extent to which the suppression effect by high [CO 2 ] may exert on the control points (electron flow, ATP and DMADP) in the synthesis of isoprene. Improving the understanding of the mechanistic basis of isoprene emissions and their importance in prediction models related to volatile organic compounds (VOC) emissions under different scales and environmental conditions.