Environmental Plant Metabolism

One of the most fascinating challenges mankind will face in the 21st century, and later, is the impact of climate change on the terrestrial biosphere and its repercussions for ecosystems’ carbon (C) balance and sustainability. Ecosystem C balance is the difference between photosynthetic CO2 uptake and respiratory CO2 release. Ecosystems are sustainable when this difference remains positive. Trees and plants in general are key players in maintaining this balance but climate change threatens their durability. Plants are sensitive to their environment, and changes in water availability, temperature, light or nutrients can have dramatic consequences on long-term ecosystem sustainability. My work aims to understand and model the metabolic and physiological responses of plants and ecosystems to abiotic stresses induced by climate change. My general approach to this work is to examine the response of primary metabolism to climate change, model it and integrate it into global scale models. 

My research combines theoretical and empirical approaches to disentangle the complexity of plant metabolic pathway. The empirical approach includes field measurements in temperate and sub-arctic deciduous forest as well as greenhouse environmental manipulation. The theoretical approach includes assessment of current Terrestrial ecosystems models' limitations and design and sensitivity-tests of new parameterizations for respiratory COproduction. 

Modeling Aboveground Plant Respiration

Understanding CO2/O2 respiratory fluxes in the light

Respiratory metabolism is divided in two fundamental parts: the electron transport chain for energy production and the tricarboxylic acid pathway (TCAP) (also known as Krebs cycle). When measuring net CO2 production using a classical gas exchange system (such as LI-6400), only decarboxylations through the TCAP can be measured. This project aims to design a new gas exchange system where both reactions could be measured at night but also in the day.

Role of photorespiration on respiratory metabolism

In C3 plants, photorespiration plays an important role in the primary metabolism of leaves. Evidences of its interaction with the respiratory metabolism has been shown. However the origin of this interaction and the environmental control of it remains unclear. This project aims to investigate the origin(s) and consequences of the interaction between photorespiration and respiration on respiratory and nitrogen metabolism in leaves on C3 plants.

Princeton University Python Community

Developing low-cost sensors for plant science


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. 

"Do all you can with what you have in the time you have in the place you are!" Xolani Nkosi