MRI of Root Zone Processes Seminar

In-situ studies of flow and transport processes in the soil-root compartment require high-resolution 3D imaging techniques. The most important ones are MRI, NT and XCT with their respective strengths of sensitivity to the solid matrix and the total water content for XCT and NT, respectively. In contrast, MRI shows no risk of radiation damage to sensitive plant tissues and root systems can be imaged with high resolution and repeatedly in time. Moreover, MRI offers the great opportunity of imaging dynamic properties such as relaxation times, diffusion coefficients and flow velocity vectors for a thorough characterization of the plant´s interaction with the soil. In the presentation, different examples of the utility of MRI for characterization of soil - root processes are given. We start with an overview of the present limits of root detectability in unsaturated porous media, and continue with the characterization of the soil zone immediately adjacent to the root surface by combination of MRI and NT[1, 2]. In a second part, slow flow processes are imaged by quantitative three-dimensional T1 mapping of a paramagnetic tracer by means of an IR-spin echo sequence[3]. We could show the enrichment near the root surface due to the interplay of advective transport by root water uptake and diffusive dilution. If flow processes are faster, MRI offers the opportunity of direct visualization by diffusion coefficient or flow velocity imaging [4, 5]. Flow velocities in porous media down to 60 micron/s are accessible with the 13interval PFG STEMSI sequence. Main features are minimum time laps between excitation and detection and compensation of the influence of internal gradients. The applicability is demonstrated by flow imaging in homogeneous and heterogeneous porous media.

References:
1. Haber-Pohlmeier, S., et al., Microporous and Mesoporous Materials, 2017: doi.org/10.1016/j.micromeso.2017.10.046.
2. Oswald, S., et al., Physics Procedia, 2015.
3. Haber-Pohlmeier, S. et al., Water Resources Research, 2017. 53: p. 7469-7480.
4. Herrmann, K.H., et al., Journal of Hydrology, 2002. 267(3-4): p. 244-257.
5. Spindler, N., et al., Journal of Magnetic Resonance, 2011. 212(1): p. 216-223