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Item Causes and consequences of pronounced variation in the isotope composition of plant xylem water(European Geosciences Union, 2020-10) De Deurwaerder, Hannes P. T.; Visser, Marco D.; Detto, Matteo; Boeckx, Pascal; Meunier, Félicien; Kuehnhammer, Kathrin; Magh, Ruth-Kristina; Marshall, John D.; Wang, Lixin; Zhao, Liangju; Verbeeck, Hans; Earth Sciences, School of ScienceStable isotopologues of water are widely used to derive relative root water uptake (RWU) profiles and average RWU depth in lignified plants. Uniform isotope composition of plant xylem water (δxyl) along the stem length of woody plants is a central assumption of the isotope tracing approach which has never been properly evaluated. Here we evaluate whether strong variation in δxyl within woody plants exists using empirical field observations from French Guiana, northwestern China, and Germany. In addition, supported by a mechanistic plant hydraulic model, we test hypotheses on how variation in δxyl can develop through the effects of diurnal variation in RWU, sap flux density, diffusion, and various other soil and plant parameters on the δxyl of woody plants. The hydrogen and oxygen isotope composition of plant xylem water shows strong temporal (i.e., sub-daily) and spatial (i.e., along the stem) variation ranging up to 25.2 ‰ and 6.8 ‰ for δ2H and δ18O, respectively, greatly exceeding the measurement error range in all evaluated datasets. Model explorations predict that significant δxyl variation could arise from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in δxyl emerge between individuals that differ only in sap flux densities or are monitored at different times or heights. This work shows a complex pattern of δxyl transport in the soil–root–xylem system which can be related to the dynamics of RWU by plants. These dynamics complicate the assessment of RWU when using stable water isotopologues but also open new opportunities to study drought responses to environmental drivers. We propose including the monitoring of sap flow and soil matric potential for more robust estimates of average RWU depth and expansion of attainable insights in plant drought strategies and responses.Item Triple isotope variations of monthly tap water in China(Nature Publishing Group, 2020-10-12) Tian, Chao; Wang, Lixin; Jiao, Wenzhe; Li, Fadong; Tian, Fuqiang; Zhao, Sihan; Earth Sciences, School of ScienceTap water isotopic compositions could potentially record information on local climate and water management practices. A new water isotope tracer 17O-excess became available in recent years providing additional information of the various hydrological processes. Detailed data records of tap water 17O-excess have not been reported. In this report, monthly tap water samples (n = 652) were collected from December 2014 to November 2015 from 92 collection sites across China. The isotopic composition (δ2H, δ18O, and δ17O) of tap water was analyzed by a Triple Water Vapor Isotope Analyzer (T-WVIA) based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technique and two second-order isotopic variables (d-excess and 17O-excess) were calculated. The geographic location information of the 92 collection sites including latitude, longitude, and elevation were also provided in this dataset. This report presents national-scale tap water isotope dataset at monthly time scale. Researchers and water resource managers who focus on the tap water issues could use them to probe the water source and water management strategies at large spatial scales.