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

• Published in: Journal of the Royal Society interface Vol. 14; no. 136; p. 20170560
• Main Authors: Keyes, S. D., Cooper, L., Duncan, S., Koebernick, N., McKay Fletcher, D. M., Scotson, C. P., van Veelen, A., Sinclair, I., Roose, T.
• Format: Journal Article
• Language: English
• Published: England The Royal Society 01.11.2017; The Royal Society Publishing
• Subjects: Compacted soils; Computed tomography; Corn; Correlation analysis; Deformation; Deformation mechanisms; Elongation; Life Sciences–Earth Science interface; Moisture content; Plant roots; Plant Roots - growth & development; Rhizosphere; Roots; Soil; Soil analysis; Soil columns; Soil compaction; Soil conditions; Soil water; Structural Imaging; Synchrotron; Synchrotrons; Three dimensional analysis; Tips; Tomography; Tomography, X-Ray Computed; Tracking; Water content; X-Ray Computed Tomography; Zea mays - growth & development; X-ray computed tomography; synchrotron; structural imaging
• ISSN: 1742-5689; 1742-5662
• DOI: 10.1098/rsif.2017.0560

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.