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Disentangling source water and leaf water signals in highly resolved oxygen isotope data from tree rings

English title Disentangling source water and leaf water signals in highly resolved oxygen isotope data from tree rings
Applicant Treydte Kerstin
Number 175888
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Research Inst. WSL Direktion
Institution of higher education Swiss Federal Institute for Forest, Snow and Landscape Research - WSL
Main discipline Other disciplines of Environmental Sciences
Start/End 01.05.2018 - 30.04.2021
Approved amount 274'476.00
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All Disciplines (2)

Discipline
Other disciplines of Environmental Sciences
Biochemistry

Keywords (5)

climate; oxygen isotopes; tree rings; ecophysiology; hydrological cycle

Lay Summary (German)

Lead
Sauerstoff-Isotope in Jahrringen
Lay summary

Der Einblick in die physiologische Reaktion von Bäumen auf Umweltveränderungen ist von höchster Relevanz für Prognosen darüber, wie das Baumwachstum und der terrestrische Kohlenstoff- und Wasserkreislauf auf zukünftige Umweltveränderungen reagieren werden. Stabile Isotope in Jahrringen sind wichtige Werkzeuge, um diese Zusammenhänge zu untersuchen, da die meisten klimatischen und physiologischen Prozesse zu spezifischen Isotopenfraktionierungseffekten führen. Sauerstoffisotope in Jahrringen können wertvolle Erkenntnisse über die Wasseraufnahme von Bäumen und ihre physiologische Reaktion auf hydroklimatische Schwankungen liefern. Das Zusammenspiel zwischen den im Quellwasser mitgeführten Isotopensignalen und denen, die auf Blattebene durch Verdunstungsanreicherung und post-photosynthetische Prozesse erzeugt werden, ist jedoch noch nicht gut verstanden, so dass die mechanistische Interpretation von Jahrringisotopen-Zeitreihen problematisch bleibt. Dies gilt insbesondere dann, wenn mechanistische Isotopenmodelle zur Simulation oder Interpretation von Jahrringisotopen als Teil von dynamischen globalen Vegetationsmodellen (DGVMs) eingesetzt werden. Das übergeordnete Ziel des vorgeschlagenen Projekts ist die nahtlose Entflechtung der Quellwasser- und Blattwassersignale in Jahrring-Isotopen für ihre ultimative Verwendung als klimatischer und baumphysiologischer Proxy. Konkret erstreben wir 1) die Quantifizierung von Umweltsignalen mit hoher intraannueller Auflösung, 2) die Identifizierung von Schlüsselfraktionierungs- und -austauschprozessen entlang des Isotopenweges vom Blatt zum Jahrring durch mechanistische Modellierung; und vor allem 3) die Bestimmung des relativen Beitrags von Quellwasser und evaporativer Blattwasseranreicherung auf saisonaler und interannueller Ebene. Das Projekt wird systematisch empirische Daten mit mechanistischen Modellen und einem Bewässerungsexperiment mit Gletscherwasser kombinieren.

Direct link to Lay Summary Last update: 27.06.2018

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Associated projects

Number Title Start Funding scheme
166162 Compound-specific dual isotope analysis for the investigation of plant response to environmental change 01.08.2016 Project funding (Div. I-III)
136295 iTREE-Long-term variability of tree growth in a changing environment - identifying physiological mechanisms using stable C and O isotopes in tree rings. 01.04.2012 Sinergia
130112 Isotope pathway from atmosphere to the tree ring along a humidity gradient in Switzerland 01.09.2010 Project funding (Div. I-III)
189724 High-resolution stable isotope analysis for tracing environmen-tal changes - HIRES 01.01.2020 R'EQUIP
150205 Coupling stem water flow and structural carbon allocation in a warming climate: the Lötschental study case (LOTFOR) 01.06.2014 Project funding (Div. I-III)

Abstract

Insight into the trees’ physiological response to environmental change is of highest relevance for predicting how tree growth and thus the terrestrial carbon and water cycle will respond to future environmental change. Stable isotope ratios in tree tissues and particularly tree rings are key tools to examine these relationships as most climatic and physiological processes result in specific isotopic fractionation effects. Oxygen isotopes in tree rings (d18Otree-ring) can provide valuable insight into the water uptake by trees and their physiological response to hydroclimatic variation. It is, however, still unclear, what determines the d18O values of a tree’s source water, how it is coupled to d18O variation of precipitation and how it is reflected in the tree ring d18Otree-ring in relation to leaf water 18O enrichment. Particularly the interplay between isotopic signals carried in the source water and those produced at the leaf level by evaporative enrichment and physiological (post-) photosynthetic processes is still not well understood and hence, the mechanistic interpretation of d18Otree-ring time-series remains problematic. This holds especially when mechanistic isotope models are employed to simulate or interpret d18Otree-ring values as part of dynamic global vegetation models (DGVMs), which integrate many hydrological and physiological processes and could improve proxy-model comparisons.The overall objective of the proposed project is to seamlessly disentangle source water and leaf water signals in d18Otree-ring records for their ultimate use as climatic and tree physiological proxy. To achieve this aim, we will mainly built upon a unique data set of highly resolved environmental, sapflow, xylogenesis and most importantly d18O data of precipitation, soil, xylem and needle water from two physiologically differing species and three ecologically differing sites within the long-term monitoring transect Lötschental/Switzerland. In addition we will produce a well-replicated set of highly resolved d18Otree-ring records by applying a worldwide unique UV-laser microscopic dissection system at the Geo Research Center Potsdam. Furthermore, at one of our study sites we will conduct an irrigation experiment by irrigating mature trees with glacier water during a dry period in summer. Combining this great set of highly resolved empirical data with the most advanced mechanistic models of isotope fractionation in the leaf, during downstream transport and metabolic processes and wood synthesis will provide an unrivalled integrated overview of the pathways and environmental dependencies of tree-ring oxygen isotope signals and, most importantly the relatie contribution of leaf water signals and source water signals to the tree ring isotopic signature. Our findings will lead to an improved understanding of the remaining portion of unexplained variance in statistically derived climate reconstructions and should help decrease the uncertainty range in those records. Moreover, results of our data-model fusion approach will allow constrain isotope-enabled modules of DGVM frameworks to provide multiple and long-term observational constraints on model dynamics and the water cycling in terrestrial ecosystems. With that we will also contribute to an improved understanding of the mechanisms governing the terrestrial water cycle processes at the atmosphere-plant continuum under environmental change, and the implications for future biogeochemical cycles. With that we are also perfectly aligned with the research questions addressed in the Swiss Forest Lab, in particular with the study of alterations of the metabolic and biogeochemical cycles in relation to increased climate variability.
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