Capturing 3D Water Flow in Rooted Soil by Ultra-fast Neutron Tomography

Recent advances in imaging techniques provide new ways for studying root-soil interactions non-invasively promoting a better understanding of the dynamic transport of water and nutrients through the rhizosphere. Neutron imaging has proven a unique tool to study the architecture of root systems together with the water distribution in the surrounding soil in situ [1]. Due to its high temporal resolution 2D neutron radiography is capable to capture dynamic changes in the local water distribution of the sample. Using D₂O as tracer substance it has been successfully applied to visualize water transport phenomena in plants, e.g. root uptake, axial transport in the xylem and the formation of embolisms. Though providing valuable new insights the analysis of water flows was intrinsically restricted by the two-dimensional imaging approach. A tomographic approach is needed to extend the observation to three dimensions, however, insufficient time resolution (the acquisition of a neutron tomogram usually takes more than one hour) has certainly been the greatest obstacle for visualizing three-dimensional flows. Drastic acceleration of the acquisition process is, therefore, necessary to resolve the water dynamics of the rhizosphere in three dimensions. Employing a new exposure mode we boosted the acquisition speed achieving time resolutions of 10 s per tomogram. This technical breakthrough paves the way for dynamic studies of three flow processes in porous media. Performing a series of tracer experiments we succeeded to visualize an ascending water front in the soil column including the subsequent root water uptake time-resolved in three dimensions [2].

References

[1] A.B. Moradi et al. Three-dimensional visualization and quantification of water content in the rhizosphere. New Phytologist 192, 653-663, 2011

[2] C. Tötzke et al. Capturing 3D Water Flow in Rooted Soil by Ultra-fast Neutron Tomography. Scientific Reports 7, 6192, 2017