Quantification of root water uptake distribution of winter barley using water stable isotopes under field conditions

Abstract

From carbon dating to hydrology, isotopic approaches have a wide range of applications, such as the study of climate change or nutrients cycling in soils. Water stable isotopic analysis is also a promising tool to better understand water dynamics in soil since it can be used to trace root water uptake at different depths. This MSc thesis had two objectives: one technical and one scientific. The first technical objective was a proof of concept in the field of a novel soil water vapour extraction method. This method had already been tested and calibrated in laboratory by Rothfuss et al. which considers isotopic thermodynamic equilibrium between soil liquid water and soil water vapour and the unique requirement of a temperature correction. The second scientific objective was the determination of the vertical root water uptake profile of winter barley crops from isotopic information. This has been done via a multi-sources mixing model (SIAR) that confronts stable isotopic compositions of soil water across depth, with stable isotopic compositions of crop xylem sap water. From a technical aspect, the gas-permeable tubing method is working properly in the field. It provides enough water quantities to be analysed off-line with a laser spectrometer. This study however outlines fractionation errors during the sampling. This work provides insight into RWU patterns of winter barley for its last stage development. Furthermore, this study underlines the importance of input data when using multi-sources mixing model. The sources isotopic signatures have to be discriminative so that the model can differentiate them. Extra parameters such as the root length density and soil water content are essential to provide thorough results.