Use of nuclear magnetic resonance microscopy for noninvasive observations of root-soil water relations

Abstract

As part of our strategy to study root-soil water relationships, it was necessary to develop a nondestructive technique to detect small changes in water distribution in and near the root. Nuclear magnetic resonance imaging (MRI), clinically used to nondestructively and noninvasively acquire anatomical information, can also be used to observe water distribution in roots, soils and other plant tissues. In MRI, a sample is placed in a strong magnetic field and a sequence of radio frequency (rf) pulses and magnetic field gradients is used to measure the concentration and relaxation properties of protons, chiefly those associated with water. This information is then reconstructed into a digital image representing the spatial distribution of water in plant tissues and soil. Today, intact roots less than 1 mm in diameter growing in soil or synthetic media can be clearly imaged in less than 4 minutes at resolutions typically less than 30µm. This permits rapid production of images that simultaneously distinguish temporal changes in water distribution in root tissue, the rhizosphere and the adjacent soil at microscopic levels. Applications of this technique for investigating plant-soil water relationships will be discussed.