REGULAR ARTICLE Linking transpiration reduction to rhizosphere salinity using a 3D coupled soil-plant model Natalie Schröder & Naftali Lazarovitch & Jan Vanderborght & Harry Vereecken & Mathieu Javaux Received: 19 September 2013 /Accepted: 21 November 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Aims Soil salinity can cause salt plant stress by reducing plant transpiration and yield due to very low osmotic potentials in the soil. For predicting this reduction, we present a simulation study to (i) identify a suitable functional form of the transpiration reduction function and (ii) to explain the different shapes of empirically observed reduction functions. Methods We used high resolution simulations with a model that couples 3D water flow and salt transport in the soil towards individual roots with flow in the root system. Results The simulations demonstrated that the local total water potential at the soil-root interface, i.e. the sum of the matric and osmotic potentials, is for a given root system, uniquely and piecewise linearly related to the transpiration rate. Using bulk total water potentials, i.e. spatially and temporally averaged potentials in the soil around roots, sigmoid relations were obtained. Unlike for the local potentials, the sigmoid relations were non-unique functions of the total bulk potential but depended on the contribution of the bulk osmotic potential. Conclusions To a large extent, Transpiration reduction is controlled by water potentials at the soil-root inter- face. Since spatial gradients in water potentials around roots are different for osmotic and matric potentials, depending on the root density and on soil hydraulic properties, transpiration reduction functions in terms of bulk water potentials cannot be transferred to other conditions, i.e. soil type, salt content, root density, be- yond the conditions for which they were derived. Such a transfer could be achieved by downscaling to the soil- root interface using simulations with a high resolution process model. Keywords Soil-root modelling . Salinity . Root water uptake . Stress function Plant Soil DOI 10.1007/s11104-013-1990-8 Responsible Editor: Rafael S. Oliveira. N. Schröder (*) : M. Javaux Forschungszentrum Jülich GmbH, Institute of Bio- and Geoscience Agrosphere Institute, IBG-3, 52425 Jülich, Germany e-mail: na.schroeder@fz-juelich.de N. Schröder Department of Hydromechanics and Modelling of Hydrosystems, Institute for Modelling Hydraulic and Environmental Systems, University of Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart, Germany M. Javaux Earth and Life Institute/Environmental Sciences, Universite catholique de Louvain, Croix du Sud, 2, L7.05.02, 1348 Louvain-la-Neuve, Belgium N. Lazarovitch Wyler Department for Dryland Agriculture, French Associates Institute for Agriculture and Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990 Midreshet Ben-Gurion, Israel J. Vanderborght : H. Vereecken Forschungszentrum Jülich GmbH, Institute of Bio- and Geoscience, Agrosphere Institute (IBG-3)/Centre for High-Performance Scientific Computing in Terrestrial Systems TerrSys, Jülich 52425, Germany