Description du projet
Le rôle de la hauteur dans la résistance d’un arbre à la sécheresse
Les arbres s’adaptent aux conditions de sécheresse en réduisant la transpiration des feuilles et, par conséquent, le flux de sève, évitant ainsi toute perte d’eau importante et l’embolie. Les grands arbres sont plus sensibles au stress provoqué par la sécheresse, mais les mécanismes à l’origine de cette plus grande vulnérabilité ne sont pas encore totalement compris. Le projet DISTRESS cherche à examiner la loi de Darcy sur l’écoulement des fluides pour déterminer l’influence de la hauteur de l’arbre sur les réactions à court et à long terme en situation de sécheresse. Grâce à l’analyse des différents traits des arbres tropicaux et aux données sur le débit de sève de 159 espèces de différents biomes, DISTRESS permettra de mieux comprendre la vulnérabilité des arbres à la sécheresse et contribuera à de meilleures simulations de l’effet du changement climatique sur les écosystèmes forestiers.
Objectif
Plants adjust leaf water potential and hydraulic conductance under drought through stomatal behaviour, reducing sap flow and protecting plants from extensive water loss and embolism. Due to the negative effect that vapour pressure deficit (VPD) and tree height have on canopy-scale water conductance (G), Darcy’s law predicts a decline in G due to the expected increase in VPD following climate warming, to which tall trees would be presumably more sensitive. Further work is thus needed to understand the effect that tree size has on tree response to increased VPD and drought. This project aims at (1) testing whether, at a given VPD, trees adjust different functional traits to compensate for the negative effect of height on G in (a) tropical forests and (b) at a global scale, and (2) describing the mechanisms behind these adjustments and the potential interactions with other functional processes that may impair tree response to drought stress with increasing size. We will first measure multiple functional traits (including sap flux, gas exchange and leaf and xylem water potential) on trees of different heights to test Darcy’s law predictions and evaluate the role that the trade-offs among traits play on enhanced vulnerability to drought with increasing tree size in tropical forests. In order to assess whether the studied mechanisms prevail across species and ecosystems, we will perform a global-scale analysis of sap-flow and, thus, G responses to VPD as a function of tree height using the sap-flux data from 159 species and nine different biomes gathered within SAPFLUXNET. This integrated analysis will provide a better understanding of the role that tree size plays in tree vulnerability to drought in the short (temporary physiological response) and long term (legacy effects), allowing the improvement of mechanistic models of tree response to climatic variability. Such information is essential to better simulate the impact that climate change may have on forest ecosystems.
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MSCA-IF - Marie Skłodowska-Curie Individual Fellowships (IF)Coordinateur
08193 Bellaterra
Espagne