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Research article - Peer-reviewed, 2020

Causes and consequences of pronounced variation in the isotope composition of plant xylem water

De Deurwaerder, Hannes P. T.; Visser, Marco D.; Detto, Matteo; Boeckx, Pascal; Meunier, Felicien; Kuehnhammer, Kathrin; Magh, Ruth-Kristina; Marshall, John D.; Wang, Lixin; Zhao, Liangju; Verbeeck, Hans


Stable isotopologues of water are widely used to derive relative root water uptake (RWU) profiles and average RWU depth in lignified plants. Uniform isotope composition of plant xylem water (delta(xyl)) along the stem length of woody plants is a central assumption of the isotope tracing approach which has never been properly evaluated.Here we evaluate whether strong variation in delta(xyl) within woody plants exists using empirical field observations from French Guiana, northwestern China, and Germany. In addition, supported by a mechanistic plant hydraulic model, we test hypotheses on how variation in delta(xyl) can develop through the effects of diurnal variation in RWU, sap flux density, diffusion, and various other soil and plant parameters on the delta(xyl) of woody plants.The hydrogen and oxygen isotope composition of plant xylem water shows strong temporal (i.e., sub-daily) and spatial (i.e., along the stem) variation ranging up to 25.2 parts per thousand and 6.8 parts per thousand for delta H-2 and delta O-18, respectively, greatly exceeding the measurement error range in all evaluated datasets. Model explorations predict that significant delta(xyl) variation could arise from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in delta(xyl) emerge between individuals that differ only in sap flux densities or are monitored at different times or heights.This work shows a complex pattern of delta(xyl) transport in the soil-root-xylem system which can be related to the dynamics of RWU by plants. These dynamics complicate the assessment of RWU when using stable water isotopologues but also open new opportunities to study drought responses to environmental drivers. We propose including the monitoring of sap flow and soil matric potential for more robust estimates of average RWU depth and expansion of attainable insights in plant drought strategies and responses.

Published in

2020, volume: 17, number: 19, pages: 4853-4870

Authors' information

De Deurwaerder, Hannes P. T.
Princeton University
Visser, Marco D.
Princeton University
Detto, Matteo
Princeton University
Boeckx, Pascal
Ghent University
Meunier, Felicien
Boston University
Kuehnhammer, Kathrin
University of Freiburg
Magh, Ruth
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Magh, Ruth
University of Freiburg
Marshall, John D (Marshall, John)
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Wang, Lixin
Indiana University-Purdue University Indianapolis
Zhao, Liangju
Chinese Academy of Sciences
Verbeeck, Hans
Ghent University

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