Preprints
https://doi.org/10.5194/hess-2020-680
https://doi.org/10.5194/hess-2020-680

  05 Jan 2021

05 Jan 2021

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

Insights into isotopic mismatch between soil water and Salix matsudana Koidz xylem water from root water isotope measurements

Ying Zhao1,2 and Li Wang1,3 Ying Zhao and Li Wang
  • 1State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and the Ministry of Water Resources, Yangling 712100, China
  • 2University of Chinese Academy of Sciences, Beijing 100049, China
  • 3College of Natural Resources and Environment, Northwest A&F University, Yangling 712100, China

Abstract. Increasing numbers of field studies have detected isotopic mismatches between plant xylem water and its potential sources. However, the cause of these isotopic offsets is not clear and it is uncertain whether they occur during root water uptake or during water transmission from root to xylem. Thus, we measured the specific isotopic composition (δ2H and δ18O) of soil water, groundwater, xylem water, and root water of Salix matsudana Koidz trees at high temporal resolution to analyze isotopic dynamics in the soil-root-xylem continuum. We report three main findings. First, we detected clear separation between mobile water and bulk soil water isotopic signals, supporting the two water worlds (TWW) hypothesis. Second, the isotopic composition of bulk soil water was closest to and overlapped with that of root water at 0–60 cm depths, but δ2H and δ18O values of root water at 80–160 cm depths deviated significantly from that of bulk soil water at the root-soil interface. This was likely due to separation of mobile and tightly bound soil water (as in the TWW hypothesis) and plant fractionation. The maximum differences in δ2H and δ18O between bulk soil water and root water were −8.6 and −1.8 ‰, respectively. Third, xylem water was only isotopically similar to root water at 100–160 cm depths and these root layers provided 74 % of the xylem water. In conclusion, isotopic offset occurred at the interface between the soil and S. matsudana roots, and it can be attributed to a combination of plant fractionation and TWW-type separation of bound and mobile soil water. Our study contributes to the body of knowledge on isotopic dynamics in the soil-root-xylem continuum and provides potentially valuable insights regarding isotopic offsets between soil water and xylem water of S. matsudana tree and other species in similar conditions.

Ying Zhao and Li Wang

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on hess-2020-680', Yakun Tang, 26 Jan 2021
    • CC2: 'Reply on CC1', Li Wang, 31 Jan 2021
  • RC1: 'Comment on hess-2020-680', Anonymous Referee #1, 03 Feb 2021
    • AC1: 'Reply on RC1', Li Wang, 08 Apr 2021
  • CC3: 'Comment on hess-2020-680', Yali Zhao, 08 Mar 2021
    • AC3: 'Reply on CC3', Li Wang, 08 Apr 2021
  • RC2: 'Comment on hess-2020-680', Anonymous Referee #2, 12 Mar 2021
    • AC2: 'Reply on RC2', Li Wang, 08 Apr 2021

Ying Zhao and Li Wang

Ying Zhao and Li Wang

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Short summary
At our study site during the covered period, differences in mobile and bulk soil water supported the two water worlds (TWW) hypothesis. Isotopic offset occurred at the interface between the soil and Salix matsudana roots and can be attributed to combined effects of ecohydrological separation (as in the TWW hypothesis) and isotopic fractionation. We used root water as a medium to connect the soil and plant xylem, extending our knowledge of isotopic signals in the soil-root-xylem continuum.