I joined The department of Geosciences at Princeton University, in December 2012. As a postdoctoral research associate, I developed a new system to accurately measure CO2, H2O and O2 gas fluxes on entire leaves. This method involves measuring net O2 production from the change in O2 concentration, and gross production. The change of 18O in O2, and O2/N2, are measured to high precision, allowing net and gross production to be accurately assessed at irradiances as low as a few tens of mmol m-2 s-1. In addition to these technical properties, this system is designed to measure leaves up to 140 cm2 to overcome the demand for leaf biomass required in biochemical (enzyme purification, metabolite extraction…) or NMR techniques.
In addition, my current work aims to understand how plants adapt their primary metabolism to survive under extreme conditions like in the Arctic or under drought (Gauthier et al. 2014).
An example of a problem that stimulates my research is the inhibition of leaf respiration in the light. This particular phenomenon refers to the reduction of mitochondrial decarboxylation and oxidation rates occurring when leaves are exposed to light. My previous work on primary metabolism showed that the demand for C skeletons from amino acids production limits the cyclic activity of the Krebs cycle (Gauthier et al. 2010). In fact, this demand could also be associated with the status of the nitrogen cycle within leaves (Gauthier et al 2013). To study plant metabolism, my approach is to use compound specific C or N labeling
My previous work at the Australian National University in Canberra, Australia was focussed on the effect of drought on respiration. To date, the impact of drought on respiration is still controversial as some studies report an increase, a decrease or no effect of drought on respiratory flux. This controversy becomes even more important when CO2 fertilization in a future world is added to the picture.To answer this question, I examined the effects of environmental variation on the temperature response of dark respiration in Eucalyptus globulus. These results highlighted the need to exercise caution when assuming a constant respiration vs photosynthesis ratio in predictive models. They also presented the dynamic nature of the temperature dependence of dark respiration in plants experiencing future climate change scenarios, particularly with respect to drought and elevated CO2. If these findings can be generalized to many species, this would have substantial implications for terrestrial C storage in a future, warmer world.
In 2010, I obtained a Ph. D in plant physiology at the University Paris Sud, France supervised by Guillaume Tcherkez. My thesis aimed to understand "The metabolic interactom between photosynthesis, (photo) respiration and nitrogen assimilation in C3 leaves". Carbon and Nitrogen metabolism are closely related and respiration seems to be the cornerstone of C:N balance inside leaves. This work showed that we still lack a metabolic understanding of how plants take advantage of their environment. Contrary to what was thought before, this data suggested that nitrogen and carbon assimilations are decoupled and that respiration is the cornerstone of their interaction. In other words, plants need to experience darkness to be able to use the carbon fixed by photosynthesis to assimilate nitrogen. These results allowed us to present a new model describing the nature of the Tricarboxylic Acid cycle in the light. As a consequence, G. Tcherkez and myself showed that TCA cycle is not "cyclic' in the light which is one of the reasons why respiration is inhibited in the light compared to dark respiration. Nevertheless, a lot remains to be done before total acceptation of the phenomenon, as there is still some controversy on what control such inhibition.