Imaging of Roots and Surrounding Soil by NMR Tomography and Relaxometry

The combination of 3D imaging of root system architecture and water uptake patterns is mandatory for the understanding of root water uptake processes. A very convenient tool for this is magnetic resonance imaging (MRI). The differentiation between roots and surrounding soil is achieved by using a comparative long echo time so that the signal from the soil is suppressed due to its much shorter T2 relaxation time (10 - 25ms) in contrast to the root tissue (ca. 60ms). Depending on a given system diameter we achieve a resolution of up to 0.16 mm for the root system which allows a reliable visualization of the entire root system. The power of the method is demonstrated by the investigation of a time series of root growth during increasing drought stress combined with a simultaneous monitoring of water content changes with high resolution of 1.56 mm. Desiccation starts first in the outer, less rooted regions of the pot. In the inner regions with a dense network of roots water content remains higher in the neighborhood of the roots. A challenging goal is to investigate the local NMR properties of soil and roots by implanting micro coils (< 2x2 mm^2) directly in the soil and the neighborhood of the roots. This offers the opportunity of obtaining local relaxation times and indirectly hydraulic parameters in larger setups like lysimeters.