Background and aims
Knowledge of plant water fluxes is critical for assessing mechanistic processes linked to biogeochemical cycles, yet resolving root water transport dynamics has been a particularly daunting task. Our objectives were to demonstrate the ability to non-invasively monitor individual root functionality and water fluxes within Zea mays L. (maize) and Panicum virgatum L. (switchgrass) seedlings using neutron imaging.
Seedlings were propagated for 1–3 weeks in aluminum chambers containing sand. Pulses of water or deuterium oxide were then tracked through the root systems by collecting consecutive radiographs during exposure to a cold-neutron source. Water flux was manipulated by cycling on a growth lamp to alter foliar demand for water.
Neutron radiography readily illuminated root structure, root growth, and relative plant and soil water content. After irrigation there was rapid root water uptake from the newly wetted soil, followed by hydraulic redistribution of water through the root system to roots terminating in dry soil. Water flux within individual roots responded differentially to foliar illumination based on supply and demand of water within the root system.
Sub-millimeter scale image resolution revealed timing and magnitudes of root water uptake, redistribution within the roots, and root-shoot hydraulic linkages—relationships not well characterized by other techniques.
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We thank Stan Wullschleger for discussion, Terry Pfeiffer for editorial assistance, Lowell Crow and Lakeisha Walker for beam line assistance and J-C Bilheux and Keely Willis for image reconstruction. Research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, and by the Joint Directed Research and Development Program with the University of Tennessee – Knoxville. The High Flux Isotope Reactor is supported by the Division of Scientific User Facilities, Office of Basic Energy Sciences, U.S. Department of Energy.
This work was supported by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
Responsible Editor: Rafael S. Oliveira.
Electronic supplementary material
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12-hour image sequence of water uptake and transport dynamics for 10-day old maize seedling #2 (Fig. 2) following addition of a pulse of D2O. Notice the root system and stem are progressively revealed as water is taken up, redistributed within the root system and transported out through the leafy stem tissue. (MPG 2562 kb)
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Warren, J.M., Bilheux, H., Kang, M. et al. Neutron imaging reveals internal plant water dynamics. Plant Soil 366, 683–693 (2013). https://doi.org/10.1007/s11104-012-1579-7
- Computed tomography
- Hydraulic redistribution
- Root water uptake
- Water transport