Deformation patterns around growing roots using X-ray CT and digital volume correlation

As roots grow into soils, particles are displaced causing a process of soil restructuring in the vicinity of the roots. To date, a systematic approach to the investigation of factors influencing deformation patterns, including displacement and strain, has not been conducted. To achieve this objective, a soil column experiment was performed within a growth chamber, designed to compare the impact of two factors – substrate and maize (Zea mays L.) genotype – on the observed patterns. X-ray computer tomography (X-ray CT) scans obtained prior to the initiation of root growth provided a reference state, while the deformed state was examined after a period of six days. Digital volume correlation (DVC) was applied with DaVis (LaVision, Göttingen, Germany) and resulting values were localized in relation to the root. In sand, the ratio of root volume to soil volume was higher, and diameters of tap roots and seminal roots were larger than in loam. The extent and the magnitude of radial displacement (displace_rad) around roots were more pronounced in the sand, and a wider strain zone was found around tap roots in this substrate. In loam, the roots with a larger diameter (>0.8 mm) cause more deformation, whereas in sand diameter class had less impact on the amount of deformation. The genotype with root hairs was associated with a larger extent of soil deformation around the root. As high displacement values throughout the samples overshadowed local particle movement, strain has been shown to be a more reliable measure for depicting deformation patterns around roots.