Hdr Année : 2019

Ecophysiological modelling of the exchanges of CO18O and COS in terrestrial ecosystems: applications to the estimation of photosynthetic and respiratory fluxes at continental and global scales

Modélisation éco-physiologique des échanges de C18OO et COS dans les écosystèmes terrestres: application à l’estimation des flux de photosynthèse et respiration aux échelles continentales et planétaires

Résumé

This manuscript presents a synthesis of the research I have conducted over the past 12 years in the “Functional Ecology and Environmental Physics” unit (EPHYSE) and, since 2014, in the “Soil- Plant-Atmosphere Interactions” unit (ISPA). The year 2007 is when I became “senior researcher” (CR1) at INRA. More importantly, it corresponds to the launch of my first multi-partner research project as principal investigator, the ANR-funded project MIST (“Modelling Isotope Signals in Tree-rings”, 2007-2011). Thus 2007 marks well the beginning of my activities of “direction of research”. Over those 12 years, my research has been organised around 4 general themes, rapidly summarised in the Appendix I of this document. The core of the manuscript focuses on one of these research themes: the development of multi-tracer approaches to predict with better accuracy photosynthetic and respiratory fluxes over land. The tracers of interest here are the oxygen isotope composition of CO2 (C18OO) as well as carbonyl sulphide (COS). This activity around these two complementary tracers of the C cycle consumed a large part of my recent years of research and involves the work of many collaborators and students. There was thus plenty of material for a thesis, and allowed me to go more deeply into the subject. In chapter 1, I give a brief historical overview of our understanding of the contemporary global C cycle and its link to the climate of the Earth. This naturally sets the rationale behind the on-going international effort to improve our predictions of the land C sink. It also naturally introduces the principles of using C18OO and COS as tracers of photosynthetic and respiratory fluxes over land as well as their pros and cons with respect to other approaches. In chapter 2, I review in more details the recent (last 10 years) literature on the exchange of C18OO and COS between soils and the atmosphere. By doing so, I also summarise results from several articles that I co-authored recently on the subject and indicate how I envisage incorporating this new knowledge into land surface models for global scale applications. I close this chapter with a priority list of remaining questions to be addressed and future directions to be taken. In chapter 3, I review our most recent understanding of the exchange of C18OO and COS between foliage and the atmosphere. This chapter also summarises results from several articles that I co-published recently on the subject. I also present unpublished results to illustrate how these new theories of COS and C18OO fluxes from foliage can be simplified and incorporated into global land surface models, using readily available parameters such as the maximum carboxylation rate of each plant functional type. I finally close the chapter listing remaining questions to be addressed. Writing this memoire gave me the occasion to think more deeply about the motivations that push me and my colleagues to develop these multi-tracer approaches and what needed to be done to better promote them amongst the global C cycle research community. These ideas are developed in chapter 1 and briefly summarised in chapter 4 in the light of the results presented in chapters 2 and 3.
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tel-04954774 , version 1 (18-02-2025)

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  • HAL Id : tel-04954774 , version 1

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Jérôme Ogée. Ecophysiological modelling of the exchanges of CO18O and COS in terrestrial ecosystems: applications to the estimation of photosynthetic and respiratory fluxes at continental and global scales. Environmental Sciences. Université de Bordeaux (UB), 2019. ⟨tel-04954774⟩
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