Team : Sureau

ANR project, 01/2018-07/2023

Link of project presentation : https://anr.fr/Projet-ANR-18-CE20-0005

Project manager : Hervé Cochard

Presentation

Droughts cause more dieback in forests when they are associated with heat waves, as during the summer of 2003 in France. However, the underlying physiological mechanisms of these diebacks remain to be elucidated. The main objective of this project is to explore a new mortality hypothesis, according to which xylem hydraulic failure is caused by a sudden increase in residual cuticular water loss (g_min) above a critical temperature Tp. Tp values ​​from the literature and preliminary simulations of a new mechanistic model (SurEau) justify this hypothesis.
We will measure g_min and its temperature dependence for forest tree species spanning a wide range of drought tolerance. For two species threatened by climate change (Fagus sylvatica and Abies alba), we will explore the variability of g_min across provenances of contrasting origins within their natural range by working on both provenance and in situ tests. g_min will also be compared for poplar genotypes contrasting for their drought tolerance. The phenotypic plasticity of this trait will be assessed for a poplar genotype grown in environments controlled for soil moisture, shade, and temperature. We will develop a new tool for g_min and Tp phenotyping that will be distributed to all project partners.
We hypothesize (H1) that species, genotypes, and phenotypes more resistant to heatwave droughts exhibit lower and more thermostable g_min. The underlying physical mechanisms will be investigated on real and biomimetic cuticles. The chemical composition of leaf cuticles will be measured on plant material selected from previous experiments to identify key structural components associated with inter- and intraspecific variation in g_min. The effect of these components on g_min and its thermostability will be assessed in biosynthetically engineered Arabidopsis mutants. We hypothesize (H2) that the thermostability of g_min is caused by the presence or proportion of specific molecules in the cuticle. Experimental tests will be conducted ex-situ under controlled conditions to assess the impact of a heatwave drought on hydraulic failure and tree mortality in order to validate the predictions of the SurEau model. This will require the parameterization of an explicit 3D model of leaf temperature combining both leaf cooling by latent heat and leaf heating by radiative effect. Finally, we will couple the SurEau model with forest flow models to predict the risk of tree mortality at ICOS-France sites. Future mortality risks caused by heatwave droughts will be predicted for these stands under several climate scenarios. A consortium of researchers including ecophysiologists, biomolecular scientists, chemists, physicists and modelers will ensure the success of the project.The main contribution of our project will be to advance our understanding of tree resistance to heatwave drought events. We will propose new key physiological traits, new phenotyping tools, and putative genes that will help breeders screen genotypes better adapted to future climate conditions. The project deliverables will consist of a list of beech and fir species and provenances that potentially perform better under high drought conditions. Finally, we will improve ecosystem functioning models used to assess climate change impacts on forests by including desiccation processes related to heatwave droughts.

Partners

ICCF INSTITUT DE CHIMIE DE CLERMONT-FERRAND
Ecologie des Forêts Méditerranéennes

Funding source

ANR