Uncorrected soil water isotopes through cryogenic vacuum distillation may lead to a false estimation on plant water sources

• Published in: Methods in ecology and evolution Vol. 14; no. 6; pp. 1443 - 1456
• Main Authors: Yang, Bin, Dossa, Gbadamassi G. O., Hu, Yue‐Hua, Liu, Lu‐Lu, Meng, Xian‐Jing, Du, Yi‐Yuan, Li, Jia‐Yuan, Zhu, Xi‐Ai, Zhang, Yong‐Jiang, Singh, Ashutosh K., Yuan, Xia, Wu, Jun‐En, Zakari, Sissou, Liu, Wen‐Jie, Song, Liang
• Format: Journal Article
• Language: English
• Published: London John Wiley & Sons, Inc 01.06.2023; Wiley
• Subjects: Clay soils; Distillation; Distilled water; Ecological studies; eco‐hydrology; Environmental factors; extraction technique; Hydrology; inter‐laboratory comparison; Isotopes; isotopic offsets; Laboratories; Loam soils; Moisture content; Offsets; Predictions; Reliability; Sensitivity analysis; Soil properties; Soil temperature; Soil types; Soil water; Stable isotopes; Stream water; Vacuum; Vacuum distillation; Water content; Water uptake
• ISSN: 2041-210X; 2041-210X
• DOI: 10.1111/2041-210X.14107

Successful use of stable isotopes (δ2H and δ18O) in ecohydrological studies relies on the accurate extraction of unfractionated water from different types of soil samples. Cryogenic vacuum distillation (CVD) is a common laboratory‐based technique used for soil water extraction; however, the reliability of this technique in reflecting soil water δ2H and δ18O is still of concern. This study examines the reliability of a newly developed automatic cryogenic vacuum distillation (ACVD) system. We further assessed the impacts of extraction parameters (i.e. extraction time, temperature and vacuum) and soil properties on the recovery of soil water δ2H and δ18O for the ACVD and traditional cryogenic vacuum distillation (TCVD) systems. Finally, we investigated the potential influence of CVD (ACVD and TCVD) technique on the prediction of plant water uptake through a sensitivity analysis. Both ACVD and TCVD similarly extracted water from the rewetted soils, but none of the CVD systems successfully recovered the isotopic signatures of doped water from soil materials. Mean δ2H offsets of extracted soil water were −2.6 ± 1.3‰ and −2.4 ± 1.7‰ for ACVD and TCVD, respectively, while mean δ18O offsets were −0.16 ± 0.14‰ and −0.39 ± 0.37‰. The isotopic offsets of CVD systems were positively correlated with soil clay content, and negatively correlated with soil water content. Using corrected soil data (with CVD offsets) could improve the prediction of plant water uptake based on its high correlation with the environmental factors. This study identifies the isotopic offsets of CVD systems (i.e. ACVD and TCVD) and provides possible solutions for better predicting plant water sources. Even though, the wide use of CVD techniques probably induce noticeable uncertainties in the prediction of plants water uptake depths. The dataset of soil water extraction in this study will have implications for the technological development of CVD techniques. 摘要 若要将氢 (δ2H) 和氧 (δ18O) 稳定同位素成功应用到生态水文学研究中，准确提取不同类型土壤中液态水而不发生同位素分馏效应是至关重要的技术环节之一。低温真空提取 (CVD) 是一种实验室内广泛使用的土壤水抽提技术，然而，CVD在提取土壤水δ2H和δ18O时的可靠性却饱受争议。. 本研究检验了一种新近发明并商业化的全自动低温真空提取 (ACVD) 技术的可靠性。我们首次系统评价了提取系统参数 (如，抽提时长、抽提温度和真空度) 和土壤质地对ACVD提取土壤水的影响，并进一步将该技术与传统低温真空提取 (TCVD) 技术进行了实验室间比较。在此基础上，我们以水分溯源研究案例为切入口探讨了两种低温真空提取 (包括ACVD和TCVD) 技术对植物水分获取深度预测的潜在干扰。. 本研究表明，ACVD和TCVD技术在提取及恢复浸润土壤水时的可靠性表现不相上下。但是，二者均未能成功复原添加到干土壤中液态水δ2H和δ18O的初始值。ACVD和TCVD提取土壤水δ2H的平均偏差分别是 −2.6 ± 1.3‰和 −2.4 ± 1.7‰，二者提取土壤水δ18O的平均偏差分别是−0.16 ± 0.14‰和 −0.39 ± 0.37‰。进一步地，上述土壤水δ2H和δ18O提取偏差与待提取土壤黏土含量和土壤含水量分别成正、反相关。敏感性分析证明，合理校正ACVD或TCVD提取的土壤水δ2H和δ18O数据可显著提升植物水分溯源结果的科学性和准确性。. 本研究证实了CVD技术在提取土壤水过程中极可能引入难以忽视的同位素偏差。与此同时，我们尝试提供了一种弱化该同位素偏差对相关研究影响的校正方法。尽管如此，我们仍担忧当前各实验室内广泛使用的CVD方法会提升稳定同位素生态水文学研究结果的不确定性。鉴于本研究仍存诸多不足，殷切期望更多科研工作和专业人员不断努力以完善土壤水提取技术或设备。.