RESTART

Unraveling the role of souRce water-related ecophysiological processEs in the Spatial-Temporal pAtterns of tree-Ring water isoTope series, RESTART, is a research project funded by the Spanish Research Agency (AEI) and led by Elisabet Martínez-Sancho, a forest ecologist, ecophysiologist, and dendrochronologist based at the University of Barcelona and Emilia Gutiérrez, who pioneered tree-ring research in the Iberian Peninsula. The project also counts on international dendrochronologists, modellers and ecophysiologists for specific working packages.

In short, RESTART aims to to reconstruct temporal patterns of climate and and tree water sources (precipitation, xylem water) based on tree-ring water stable isotope chronologies gaining understanding of the role of forests in the water cycle. For that, we need to incorporate into a modelling framework all the isotopic fractionation and mixing processes occurring since a rain drop reaches the soil and until the oxygen and hydrogen atoms are fixed in the molecules of cellulose forming the tree-rings. My main contribution will be during the first part of the process: understanding the spatiotemporal patterns in root water uptake and their effect on the isotopic composition of xylem water. See a more detailed project description below. The project will be conducted mainly in the Vallcebre Research Catchments and the Massif of Pedraforca in the Catalan PrePyrenees.

Project description

Forests play a crucial role in modulating the water cycle. Through transpiration, trees release significant amounts of water into the atmosphere along with transpiration. In the current context of climate change, determining the water source used by trees is important to quantify the portion of water that will not be available for other systems such as rivers and/or groundwater recharge. Water isotopes (d18O and d2H) are ideal tracers to investigate water fluxes among compartments of the water cycle. The application of stable isotopes has proven to be a useful methodology for studying the role of vegetation and its water sources, but the temporal resolution of these studies is often limited to short periods.

Tree-ring series represent an invaluable temporal archive that records information about the environmental, hydrological, and physiological conditions under which atmospheric CO2 and H2O were absorbed and partitioned to growth. The application of stable isotopes in dendrochronology has shown great potential for reconstructing hydroclimatic conditions. However, there are still knowledge gaps regarding the origin and mechanisms from which these signals derive. Recent studies suggest that the isotopic content of tree rings correlates better with the isotopic signals of the tree water source than with internal tree evaporative processes. In this case, stable isotope series obtained from tree rings would provide a long-term temporal perspective on the isotopic composition of precipitation and the water sources of the trees, connecting atmosphere-hydrology-vegetation. To achieve this, a profound understanding of isotopic fractionation in water due to internal tree processes, including those related to d2H, and a detailed characterization of the various components of the isotopic pathway, especially those related to the water source, are required.

The overall aim of the RESTART project is to reconstruct temporal patterns of climate and and tree water sources (precipitation, xylem water) based on tree-ring water stable isotope chronologies gaining understanding of the role of forests in the water cycle. Specifically, we will 1) identify the temporal patterns of tree source water by assessing the isotope fractionation pathway from precipitation to xylem water, 2) investigate the environmental signals of the different isotopic components and how they are reflected in the cellulose of the rings, and 3) experimentally describe how spatial variability in source water controls isotopic signals in tree-ring series. Finally, all the knowledge gained will be utilized to calibrate the process-based model MAIDENiso, which will then be employed for inverse modeling of the past climate conditions as well as the isotopic composition of precipitation and xylem water. To achieve the goal of the RESTART project, a unique interdisciplinary approach including a deep understanding of hydrology, ecophysiology, dendrochronology, and mechanistic modeling is required to resolve the remaining questions of the mechanisms and drivers governing water stable isotope signals in tree rings.