Preprints
https://doi.org/10.5194/hess-2022-142
https://doi.org/10.5194/hess-2022-142
 
03 May 2022
03 May 2022
Status: this preprint is currently under review for the journal HESS.

The natural abundance of stable water isotopes method may overestimate deep-layer soil water use by trees

Shaofei Wang1, Xiaodong Gao2,3, Min Yang1, Gaopeng Huo1, Xiaolin Song4, Kadambot H. M. Siddique5, Pute Wu2,3, and Xining Zhao2,3 Shaofei Wang et al.
  • 1Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, 712100, Yangling, Shaanxi Province, China
  • 2Institute of Soil and Water Conservation, Northwest A&F University, 712100, Yangling, Shaanxi Province, China
  • 3Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, 712100, Yangling, Shaanxi Province, China
  • 4State Key Laboratory of Crop Stress Biology for Arid Areas, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China
  • 5The UWA Institute of Agriculture, The University of Western Australia, Perth, WA 6001, Australia

Abstract. Stable water isotopes have been used extensively to study the water use strategy of plants in various ecosystems. In deep vadose zone (DVZ) regions, the rooting depth of trees can reach several meters to tens of meters. However, the existence of roots in deep soils does not necessarily mean the occurrence of root water uptake, which usually occurs at a particular time during the growing season. Therefore, quantifying the contribution of deep-layer soil water (DLSW) in DVZ regions using the natural abundance of stable water isotopes may not be accurate because this method assumes that trees always extract shallow- and deep-layer soil water. We propose a multi-step method for addressing this issue. First, isotopic labeling in deep layers identifies whether trees absorb DLSW and determines the soil layer depths from which trees derive their water source. Next, calculate water sources based on the natural abundance of stable isotopes to quantify the water use strategy of trees. We also compared the results with the natural abundance of stable water isotopes method. The 11- and 17-year-old apple trees were taken as examples for analyses on China’s Loess Plateau. Isotopic labeling showed that the water uptake depth of 11-year-old apple trees reached 300 cm in the blossom and young fruit (BYF) stage and only 100 cm in the fruit swelling (FSW) stage, whereas 17-year-old trees always consumed water from the 0–320 cm soil layer. Overall, apple trees absorbed the most water from deep soils (> 140 cm) during the BYF stage, and 17-year-old trees consumed more water in these layers than 11-year-old trees throughout the growing season. In addition, the natural abundance of stable water isotopes method overestimated the contribution of DLSW, especially in the 320–500 cm soil layer. Our findings highlight that determining the occurrence of root water uptake in deep soils helps quantify the water use strategy of trees in DVZ regions.

Shaofei Wang et al.

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-2022-142', Anonymous Referee #1, 10 Jun 2022
    • AC1: 'Reply on RC1', Xiaodong Gao, 29 Jul 2022
  • RC2: 'Comment on hess-2022-142', Anonymous Referee #2, 09 Aug 2022
    • AC2: 'Reply on RC2', Xiaodong Gao, 12 Sep 2022

Shaofei Wang et al.

Shaofei Wang et al.

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Short summary
Water uptake depth of 11-year-old apple trees reached 300 cm in the blossom and young fruit stage and only 100 cm in the fruit swelling stage, whereas 17-year-old trees always consumed water from 0–320 cm soil layer. Overall, the natural abundance of stable water isotopes method overestimated the contribution of deep soil water, especially in the 320–500 cm soils. Our findings highlight that determining the occurrence of root water uptake in deep soils helps quantify trees water use strategy.