Where do roots take up water? Neutron radiography of water flow into the roots of transpiring plants growing in soil

Abstract

SummaryWhere and how fast does water flow from soil into roots? The answer to this question requires direct and in situ measurement of local flow of water into roots of transpiring plants growing in soil.We used neutron radiography to trace the transport of deuterated water (D 2 O) in lupin (Lupinus albus) roots. Lupins were grown in aluminum containers (30 9 25 9 1 cm) filled with sandy soil. D 2 O was injected in different soil regions and its transport in soil and roots was monitored by neutron radiography. The transport of water into roots was then quantified using a convection-diffusion model of D 2 O transport into roots.The results showed that water uptake was not uniform along roots. Water uptake was higher in the upper soil layers than in the lower ones. Along an individual root, the radial flux was higher in the proximal segments than in the distal segments.In lupins, most of the water uptake occurred in lateral roots. The function of the taproot was to collect water from laterals and transport it to the shoot. This function is ensured by a low radial conductivity and a high axial conductivity. Lupin root architecture seems well designed to take up water from deep soil layers.

Plant Water Uptake in Drying Soils

“…For a given root, these preferential sites are predicted a few centimeters from the root tip, where protoxylem and xylem elements are conductive and hydrophobic structures are lacking. This was recently confirmed experimentally by neutron radiography experiments (Zarebanadkouki et al, 2013).…”

“…More recently, the use of neutron radiography (Esser et al, 2010) that is not bound to any specific type of substrate has been used to investigate water movement and determine water uptake sites in lupin (Lupinus albus) root systems. Using D 2 O injection in combination with a convection-diffusion model, water uptake by individual segments could be quantified in a complete root system (Zarebanadkouki et al, 2013). This technical evolution is therefore promising new insights on the water dynamics at smaller scales, while systems analysis frameworks will help to integrate this information.…”

Visualization of Root Water Uptake: Quantification of Deuterated Water Transport in Roots Using Neutron Radiography and Numerical Modeling

“…Figure 1 shows selected neutron radiographs of D 2 O injection during the day and night. This figure is modified from Zarebanadkouki et al (2013). The radiographs show that (1) the radial transport of D 2 O into the roots was faster during the day than during the night and (2) the axial transport of D 2 O along the roots was visible only during the day, while it was negligible at night.…”

“…To determine the convective fluxes from the radiographs, Zarebanadkouki et al (2012Zarebanadkouki et al ( , 2013 introduced a diffusion-convection model of D 2 O transport in roots. The model was solved analytically.…”

Challenges in imaging and predictive modeling of rhizosphere processes

“…Zarebanadkouki et al (2012) and developed a method to reconstruct the water fluxes into roots based on D 2 O injection during both day and night, and simulated the process with an advection-diffusion model of D 2 O transport into the roots. By inverse simulation of the D 2 O concentrations in the roots, the authors could reconstruct the water fluxes into a root architecture (Zarebanadkouki et al 2013). This technique was applied to measure root water uptake in soil regions that were subjected to severe drying and rewetting .…”