Understanding water flux in the xylem, from seasonal dynamics to long-term variations, from xylem cell maturation to forest ecosystems

PI : Cyrille Rathgeber (UMR 1434 SILVA)

Co-applicants : Matthias Cuntz and Laura Fernández de Uña (UMR 1434 Silva)


Context — Plants adjust leaf water potential and stomata conductance when confronted to drought, reducing sap-flow and protecting their tissues from excessive water loss. Leaf and xylem water potentials directly influence cell turgor pressure, affecting in turn xylem cell division, expansion and maturation, and thus stem radial growth, tree-ring structure, and wood quality. Potential xylem hydraulic conductivity, on the other hand, depends mainly on the size and number of its conducting elements. Understanding how xylem formation and resulting wood anatomical features interplay with water and carbon fluxes in their response to climatic variations is essential to improve vegetation models and assess forest responses to climate changes.

Objectives — The aim of this project is to study the coupling between wood formation dynamics, tree water potential, and soil-forest-atmosphere continuum water fluxes.

Approaches — The project will be based on a detailed description of the intra-annual dynamics of wood formation in a beech stand in the Hesse Forest, for which we also have records of automatic dendrometers and sap flow sensors, as well as carbon and water flux measurements according to the Eddy covariance method. These eco-physiological measurements will be related to meteorological parameters and water balance in order to evaluate the influence of environmental factors on the intra-annual dynamics of xylem conductivity.

Expected results and impacts — The results of this project will provide a better understanding of the response of trees to climate variability and interactions between the canopy, stem, and roots. The proposed research will also provide new insights into the biological processes governing the carbon and water cycle of a forest ecosystem, improving our understanding of its responses to drought at short (growth dynamics), medium (legacy effects), and long-term (forest functioning). Such information is essential to improve the representation of climate-water-carbon interactions in vegetation models, and then to better simulate the impact of climate change on the terrestrial biosphere.