Measurement of micro-scale soil deformation around roots using four-dimensional synchrotron tomography and image correlation

Abstract

This study applied time lapse (four-dimensional) synchrotron X-ray computed tomography to observe micro-scale interactions between plant roots and soil. Functionally contrasting maize root tips were repeatedly imaged during ingress into soil columns of varying water content and compaction. This yielded sequences of three-dimensional densiometric data, representing time-resolved geometric soil and root configurations at the micronmetre scale. These data were used as inputs for two full-field kinematic quantification methods, which enabled the analysis of three-dimensional soil deformation around elongating roots. Discrete object tracking was used to track rigid mineral grains, while continuum digital volume correlation was used to track grey-level patterns within local sub-volumes. These techniques both allowed full-field soil displacements to be quantified at an intra-rhizosphere spatial sampling scale of less than 300 µm. Significant differences in deformation mechanisms were identified around different phenotypes under different soil conditions. A uniquely strong contrast was observed between intact and de-capped roots grown in dry, compacted soil. This provides evidence that functional traits of the root cap significantly reduce the amount of soil disturbance per unit of root elongation, with this effect being particularly significant in drier soil.

Imaging microstructure of the barley rhizosphere: particle packing and root hair influences

“…Thicker roots are generally better at penetrating strong soils (Chimungu et al, 2015), and indeed thickening of roots in strong soils has been interpreted as a mechanism of overcoming limiting axial stress by loosening the soil at the root tip (Hettiaratchi, 1990). Furthermore, the shape of the root tip (Colombi et al, 2017b) and the release of mucilage at the root cap have been shown to influence root penetration (Iijima et al, 2003;Vollsnes et al, 2010;Keyes et al, 2017). In naturally structured soils, roots can overcome large localised mechanical impedance by compensatory extension into loose soil compartments or macropores (Bingham & Bengough, 2003;Colombi et al, 2017).…”

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

“…Zappala et al (2013) previously observed that plant health was not significantly affected provided plants were not exposed to X-rays for prolonged periods. This has also been confirmed by Keyes et al, (2017a) who monitored microscale plant root growth using SRXCT and were able to mitigate the negative effects of X-rays on plant health by limiting exposure. Finally, sections of leaf and stem, excised and mounted as described below, were imaged 25 h after the initial addition of contrast media ('Leaf Images').…”

“…We would not have captured changes in root growth caused by the addition of contrast media as the contrast media was only applied to the roots for the imaging period of 24 h and the root tips themselves were not captured. The purpose of this investigation was to assess whether our system would facilitate contrast media uptake however, were growing root tips to be imaged, such as in the work of Keyes et al, (2017a), it would be possible to capture effects of contrast media on root growth over time. In order to mitigate these effects, non-ionic iodinated contrast media should be used, such as the iopamidol used in this investigation, as ionic alternatives have previously been observed to induce more significant osmotic stress effects in biological tissues (Haller and Hizoh 2004;Hasebroock and Serkova 2009;Heinrich et al 2005;Sendeski 2011).…”

“…This stub mount was modified to hold a syringe vertically tip-down by securing the tip with a luger connection. The design of this modified SEM stub is detailed in previous studies (Daly et al 2016;Keyes et al 2017a;Keyes et al 2013). The basal tip of syringe which formed the bottom section of the root growth channel was inserted into this modified SEM stub and held tip-down such that the experimental system was vertical.…”

Disturbance function for soil disturbed state strength based on X-ray computed tomography triaxial test

“…to analyze the soil bulk density. In the recent decade, CT had been widely used to evaluate the evolution of the internal structure of soil by several researchers including Oda et al [2], Pires et al [3], Alshibli et al [4], Schäffer et al [5,6], Hall et al [7], Willson et al [8], Bruchon et al [9], Naveed et al [10] and Keyes et al [11].…”