Elucidating the impact of respiration on plant and crop carbon balance is a persisting conundrum of physiology since respiration is both detrimental to plant biomass production (carbon loss in the form of CO2) and beneficial for nutrient assimilation (such as nitrogen) and growth. Furthermore, leaf respiration is at the heart of interactions between photosynthesis, photorespiration and mitochondrial metabolism and therefore, it is believed to be orchestrated by a complex regulation network, that may in turn be influenced by environmental changes (e.g. light/dark transition, atmospheric CO2 and temperature). Still, there are presently many enduring uncertainties about respiratory function in photosynthetic organs. So is the case of (i) possible robust relationships between ecophysiological leaf traits and respiration rate, (ii) fundamental fluxes that describe respiratory gas exchange, (iii) metabolic flux patterns associated with respiration and (iv) the effect of respiration on carbon and isotopic balance. In the present project, we intend to use post-genomic approaches (mainly, proteomics, fluxomics and isotopic facilities) to better understand metabolic commitments as well as respiratory responses to environmental conditions, from the cellular to the organ level. We propose to develop mostly in vivo and analytical methods to characterize leaf respiration, identify key regulators and appreciate the impact of respiration on other metabolisms like C1-metabolism. This project takes advantage of our expertise in isotopic methods adapted for plant biology. The ‘generalized fluxomic’ approach proposed in the project (i.e. carrying out extensive flux pattern studies) should provide a neat advance in understanding the metabolic orchestration of plant respiration.