PhD student

CNRS-CEFE

1919, route de Mende
34293 Montpellier 5
France
Office 105C

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PhD thesis subject (2024-2027): Drought effects on carbon assimilation and allocation in living tree biomass in forests

Supervisors: Jean-Marc Limousin (CNRS-CEFE) and Maxime Cailleret (INRAE-RECOVER)

Forests are a major player in the global carbon (C) cycle and at the heart of the climate change mitigation initiatives of the 2015 Paris Agreement, but models strongly disagree on the projection of this C sink under future climate change. Our current understanding of climate change effects on forest’s carbon sequestration is limited by uncertainties around the allocation of carbon among the different tree organs and the link between carbon photosynthetic assimilation and sequestration in perennial tree biomass.

The main objectives of this PhD thesis are to quantify how the C allocation in tree biomass changes among the different organs (wood, roots, leaves and reproductive organs) in response to increasing water stress and decreasing C assimilation. The research project will use both the results of five long-term rainfall manipulation experiments set in different forest ecosystems (three Mediterranean forests in Southern France, one temperate forest in North-Eastern France, and one eucalypt plantation in Brazil), and of carbon fluxes measured by eddy covariance in different forest sites within the ICOS network, to study the experimental and inter-annual effects of changing water availability. It will involve the analysis and synthesis of existing data and the collection of new data using homogenized and innovative protocols in every site, especially regarding the belowground compartment that is generally understudied in forest ecosystems.

The thesis will be articulated around three main research axes: i) improve our understanding of the link between photosynthetic C uptake and wood stem growth; ii) investigate the effects of drought on tree architecture and C allocation among the different aerial tree organs; iii) quantify belowground C allocation and its response to drought.