Preprints
https://doi.org/10.5194/hess-2020-446
https://doi.org/10.5194/hess-2020-446

  16 Oct 2020

16 Oct 2020

Review status: this preprint is currently under review for the journal HESS.

A comparative study of plant water extraction methods for isotopic analyses: Scholander-type pressure chamber vs. cryogenic vacuum distillation

Giulia Zuecco1, Anam Amin1, Jay Frentress2, Michael Engel2, Chiara Marchina1, Tommaso Anfodillo1, Marco Borga1, Vinicio Carraro1, Francesca Scandellari3, Massimo Tagliavini2, Damiano Zanotelli2, Francesco Comiti2, and Daniele Penna4 Giulia Zuecco et al.
  • 1Department of Land, Environment, Agriculture and Forestry, University of Padova, Italy
  • 2Faculty of Science and Technology, Free University of Bozen-Bolzano, Italy
  • 3Isotracer s.r.l., Bologna, Italy
  • 4Department of Agriculture, Food, Environment and Forestry, University of Florence, Italy

Abstract. Recent tracer-based studies using stable isotopes of hydrogen and oxygen showed that different methods for extracting water from plant tissues can return different isotopic composition due to the presence of organic compounds and the extraction of different plant water pools. One of the most used methods to extract plant water is the cryogenic vacuum distillation (CVD), which tends to extract total plant water. Conversely, the Scholander-type pressure chamber (SPC), which is commonly used by tree physiologists to measure shoot water potential and determine plant water stress, has been rarely applied to extract plant water for isotopic analyses.

In this work, we analyzed the variability in the isotopic composition of plant water extracted by SPC and CVD, also considering the potential variability in the isotopic signature of the plant tissues (i.e., leaves, twig without bark, twig with bark, twig close to the trunk of the tree, and wood core) and plant species (i.e., alder, apple, chestnut and beech). The extraction of plant water by SPC is simple, can be carried out in situ, and it does not require specific laboratory work as in case of CVD. However, the main limitation of SPC is the very small water volume that can be extracted from the lignified shoots during conditions of water deficit, compared to CVD.

Our results indicated that plant water extracted by SPC and CVD were significantly different. The difference in the isotopic composition obtained by the two extraction methods was smaller in the beech samples compared to alder, apple and chestnut samples. The isotopic signature of alder, apple and chestnut plant water extracted by SPC was more enriched in δ2H and δ18O, respectively, than the samples obtained by CVD. We conclude that plant water extraction by SPC is not an alternative for CVD, as SPC likely extracts only water within the xylem (dead cells), whereas CVD tends to retrieve all water stored in the sampled tissue, from both living and dead cells. However, studies aiming to quantify the relative contribution of the water sources to transpiration should rely more on the isotopic composition of xylem water transpiring during the sampling day (which is theoretically sampled by SPC), than the isotopic composition of total plant water (sampled by CVD), which also contains a fraction of water that could be stored in plant tissues for long time.

Giulia Zuecco et al.

 
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Giulia Zuecco et al.

Giulia Zuecco et al.

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