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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. Methods: 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. Results: 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. Conclusions: 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. [ABSTRACT FROM AUTHOR]

Background: Our recent publication (Warren et al., Plant Soil 366:683-693, ) described how pulses of deuterium oxide (DO) or HO combined with neutron radiography can be used to indicate root water uptake and hydraulic redistribution in maize. This technique depends on the large inherent differences in neutron cross-section between D and H atoms resulting in strong image contrast. Scope and Conclusions: However, as illustrated by Carminati and Zarebanadkouki () there can be a change in total water content without a change in contrast simply by a change in the relative proportions of DO and HO. We agree with their premise and detailed calculations (Zarebanadkouki at al. , ), and present further evidence that mixing of DO and HO did not confound evidence of hydraulic redistribution in our study. [ABSTRACT FROM AUTHOR]