Quantification of root water uptake and redistribution using neutron imaging: a review and future directions

Abstract

SUMMARY Quantifying root water uptake is essential to understanding plant water use and responses to different environmental conditions. However, non‐destructive measurement of water transport and related hydraulics in the soil–root system remains a challenge. Neutron imaging, with its high sensitivity to hydrogen, has become an unparalleled tool to visualize and quantify root water uptake in vivo. In combination with isotopes (e.g., deuterated water) and a diffusion–convection model, root water uptake and hydraulic redistribution in root and soil can be quantified. Here, we review recent advances in utilizing neutron imaging to visualize and quantify root water uptake, hydraulic redistribution in roots and soil, and root hydraulic properties of different plant species. Under uniform soil moisture distributions, neutron radiographic studies have shown that water uptake was not uniform along the root and depended on both root type and age. For both tap (e.g., lupine [Lupinus albus L.]) and fibrous (e.g., maize [Zea mays L.]) root systems, water was mainly taken up through lateral roots. In mature maize, the location of water uptake shifted from seminal roots and their laterals to crown/nodal roots and their laterals. Under non‐uniform soil moisture distributions, part of the water taken up during the daytime maintained the growth of crown/nodal roots in the upper, drier soil layers. Ultra‐fast neutron tomography provides new insights into 3D water movement in soil and roots. We discuss the limitations of using neutron imaging and propose future directions to utilize neutron imaging to advance our understanding of root water uptake and soil–root interactions.

Impacts of Soil Health Practices on Hydrologic Processes

“…These macropores can aid in moving water to deeper soil depths but may also be responsible for a lack of water near the surface and decreased contaminant filtration. Recent research supports this long-standing observation on the effect of plant roots on water and solute redistribution in the soil profile (Hafner et al 2020;Cai et al 2022).…”

Promotional Properties of ACC Deaminase-Producing Bacterial Strain DY1-3 and Its Enhancement of Maize Resistance to Salt and Drought Stresses

“…The good promotional effect on all the indexes at this concentration may be due to the fact that this type of salt concentration enables the average growth of DY1-3 to produce growth substances, such as IAA and other growth substances, and, at the same time, the ACC deaminase acts synergistically with the plant, which helps to protect it against the adverse effects of the stress [61]. The increase in the relative number of root meristems of the maize seeds by the bacterial solution at ambient NaCl concentrations greater than 400 mmol/L is not significant (p > 0.05), and this is because, at the seed germination stage, high-salt-stress conditions affect plant growth regulators, slowing down their physiological processes and inhibiting the dispersal of seed roots [62]; thus, maize seeds reduce the distribution of the number of root meristems to maintain adequate water and the rational use of nutrients but lengthen their main roots to better search for water [63][64][65]. The synergistic effect of strain DY1-3 with the maize seeds also followed this feature, which significantly increased the primary root length of the maize seeds compared to the control group at a salt concentration of 400-500 mmol/L (p < 0.05), and the addition of the bacterial solution resulted in a significant increase in the shoot length and vigor index of the maize seeds compared to the unaddressed group (p < 0.05).…”

Towards portable MRI in the plant sciences

“…To study plant structure, standard methods include dye tracing, microscopy techniques, X-ray tomography [ 17 , 18 ], neutron radiography [ 19 – 21 ], air-coupled ultrasound [ 22 ], laser-based guided waves [ 23 ], and 2D-light transmission [ 24 , 25 ]. Dye tracing has been used to study plant structure for almost a century [ 26 ], and functions by staining certain anatomical structures, and the distribution of dyes can be observed either macroscopically or under the microscope.…”

“…Non-invasive imaging methods permit the study of physiological processes. Root water uptake has been studied by X-ray [ 41 , 42 ] and neutron tomography [ 21 , 43 – 45 ] and also by 2D-light transmission imaging [ 24 , 25 ]. These methods enable a spatially resolved study of root water uptake.…”