Preprints
https://doi.org/10.5194/hess-2020-683
https://doi.org/10.5194/hess-2020-683

  19 Jan 2021

19 Jan 2021

Review status: a revised version of this preprint is currently under review for the journal HESS.

Potential effects of cryogenic extraction biases on inferences drawn from xylem water deuterium isotope ratios: case studies using stable isotopes to infer plant water sources

Scott T. Allen1 and James W. Kirchner2,3 Scott T. Allen and James W. Kirchner
  • 1Dept. of Natural Resources and Environmental Science, University of Nevada, Reno, USA
  • 2Dept. of Environmental Systems Science, ETH Zürich, Zürich, Switzerland
  • 3Swiss Federal Research Institute WSL, Birmensdorf, Switzerland

Abstract. Recent studies have demonstrated that plant and soilwater extraction techniques can introduce biases and uncertainties in stable isotope analyses. Here we show how recently documented δ2H biases resulting from cryogenic vacuum distillation of water from xylem tissues may have influenced the conclusions of five previous studies, including ours, that have used δ2H to infer plant water sources. Cryogenic extraction biases that reduce xylem water δ2H will also introduce an artifactual evaporation signal in dual-isotope (δ2H vs. δ18O) analyses. Calculations that estimate the composition of the source precipitation of xylem waters by compensating for their apparent evaporation will amplify the bias in δ2H, and also introduce new biases in the δ18O of the inferred pre-evaporation source precipitation. Cryogenic extraction biases may substantially alter plant water source attributions if the spread in δ2H among the potential end members is relatively narrow. By contrast, if the spread in δ2H among the potential end members is relatively wide, the impact of cryogenic extraction biases will be less pronounced, and thus suggestions that these biases universally invalidate inferences drawn from plant water δ2H are unwarranted. Nonetheless, until reliable correction factors for cryogenic extraction biases become available, their potential impact should be considered in studies using xylem water isotopes.

Scott T. Allen and James W. Kirchner

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2020-683', Anonymous Referee #1, 08 Feb 2021
    • AC1: 'Reply on RC1', Scott T. Allen, 12 Mar 2021
  • RC2: 'Comment on hess-2020-683', Ansgar Kahmen, 23 Apr 2021
  • RC3: 'Comment on hess-2020-683', Anonymous Referee #3, 04 May 2021

Scott T. Allen and James W. Kirchner

Scott T. Allen and James W. Kirchner

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Short summary
Extracting water from plant stems can introduce analytical errors in isotope analyses. We demonstrate that sensitivities to suspected errors can be evaluated and that conclusions drawn from extracted plant water isotope ratios are neither generally valid nor generally invalid. Ultimately, imperfect measurements of plant and soil water isotope ratios can continue to support useful inferences if study designs are appropriately matched to their likely biases and uncertainties.