Magali F. Nehemy (1), Paolo Benettin (2), Mitra Asadollahi (2), Dyan Pratt (1), Andrea Rinaldo (2,3), Jeffrey J. McDonnell (1,4)
(1) Global Institute for Water Security, School of Environment and Sustainability, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
(2) Laboratory of Ecohydrology, Institute of Environmental Engineering, École Polytechnique Fédérale de Lausanne, Station 2, GR C1 575, 1015 Lausanne, Switzerland
(3) Dipartimento ICEA, Università di Padova, via Loredan 20, I-35131 Padova, Italy
(4) School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, UK
Correspondence to: Magali Nehemy ([email protected])
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 15 hydraulics, fine root distribution, and soil matric potential to investigate the 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 spatiotemporal 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 20 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.