Stable isotopes of water reveal differences in plant – soil water relationships across northern environments

Doerthe Tetzlaff*, James Buttle, Sean K. Carey, Matthew J. Kohn, Hjalmar Laudon, James P. McNamara, Aaron Smith, Matthias Sprenger, Chris Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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We compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well-known long-term study sites in northern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quantitatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites isotopes in xylem water from angiosperms showed a strong overlap with soil water; this was not the case for gymnosperms. In most cases, xylem water composition on a given sampling day could be better explained if soil water composition was considered over longer antecedent periods spanning many months. Xylem water at most sites was usually most dissimilar to soil water in drier summer months, although sites differed in the sequence of change. Open questions remain on why a significant proportion of isotopically depleted water in plant xylem cannot be explained by soil water sources, particularly for gymnosperms. It is recommended that future research focuses on the potential for fractionation to affect water uptake at the soil-root interface, both through effects of exchange between the vapour and liquid phases of soil water and the effects of mycorrhizal interactions. Additionally, in cold regions, evaporation and diffusion of xylem water in winter may be an important process.

Original languageEnglish
Article numbere14023
Number of pages19
JournalHydrological Processes
Issue number1
Early online date24 Jan 2021
Publication statusPublished - 24 Jan 2021

Bibliographical note

Funding Information:
We thank the European Research Council ERC for funding (VeWa project GA 335910). Contributions from CS were supported by the Leverhulme Trust through the ISO-LAND project (RPG 2018 375). Support for MJK and JPM were provided by the US National Science Foundation (EAR0842367) and Boise State University. We thank Dr. Samantha Evans for technical support. Thanks to the Dorset Environmental Science Centre for provision of meteorological data. The work conducted in Krycklan was partly financed by SITES (VR) and the KAW Branch-Point project. We would like to acknowledge Dr. Nadine Shatilla for collection of the Wolf Creek samples and the Global Water Futures program for financial support. We also would like to sincerely thank Jeff McDonnell for his support throughout the VeWa project and all participants in the different VeWa workshops esp. Tanya Doody and Marco Maneta for their invaluable input into the discussions.


  • cold regions
  • critical zone
  • northern environments
  • soil isotopes
  • stable isotopes
  • xylem isotopes


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