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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2019-528
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-528
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 21 Oct 2019

Submitted as: research article | 21 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

How plant water status drives tree source water partitioning

Magali F. Nehemy1, Paolo Benettin2, Mitra Asadollahi2, Dyan Pratt1, Andrea Rinaldo2,3, and Jeffrey J. McDonnell1,4 Magali F. Nehemy et al.
  • 1Global Institute for Water Security, School of Environment and Sustainability, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
  • 2Laboratory of Ecohydrology, Institute of Environmental Engineering, École Polytechnique Fédérale de Lausanne, Station 2, GR C1 575, 1015 Lausanne, Switzerland
  • 3Dipartimento ICEA, Università di Padova, via Loredan 20, I-35131 Padova, Italy
  • 4School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, UK

Abstract. The stable isotopes of oxygen and hydrogen (δ2H and δ18O) have been widely used to investigate plant water source partitioning. These tracers have shed new light on patterns of plant water use in time and space. However, this black box approach has limited our source water interpretations and mechanistic understanding. Here, we combine measurements of stable isotope composition in xylem and soil water pools with measurements of plant hydraulics, fine root distribution and soil matric potential to investigate mechanism(s) driving tree water source partitioning. We used a 2 m3 lysimeter planted with a small willow tree (Salix viminalis) to conduct a high spatial-temporal resolution experiment. We found that tree water source partitioning was driven mainly by tree water status and not by patterns of fine root distribution. Source water partitioning was regulated by plant hydraulic response to changing atmospheric demand and soil matric potential. The depth distribution of soil matric potential appeared to be the largest control on the patterns of soil water partitioning during periods of tree water deficit. Contrary to the common steady state assumption in ecohydrological source water investigations, our results show that tree water use is a dynamic process, driven by tree water deficit. Overall, our findings suggest new research foci for future plant water isotopic investigations, highlighting the importance of hydrometric measurements from the plant perspective.

Magali F. Nehemy et al.
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Magali F. Nehemy et al.
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