Microsensing of water dynamics and root distributions in sandy soils

Comprehensive understanding of water and nutrient transport in the rhizosphere is important because water use is a major societal and environmental concern. Studying these processes has been slow, however, due to historical neglect of belowground research and the fact that soil is not transparent to many research tools. We investigated two independent and noninvasive methods that have the potential to expand our knowledge of root water uptake. The magnetic resonance imaging technique was used to simultaneously generate three-and two-dimensional, high-resolution images of a seedling's root system and the soil water content distribution in the rhizosphere of sandy soils. A quantitative measurement of soil moisture in the rhizosphere and specifically at the root-soil interface was applied, taking into account the cylindrical nature of roots and the radial water flow toward root surfaces. This protocol enabled a dynamic study of water depletion patterns around a single root as a result of root water uptake. In the second method, a pliable-tip microtensiometer (PTMT) was introduced as a reliable tool to measure soil water pressure heads in a small volume of sandy soil. A set of PTMTs combined with a growth chamber, which allows roots to grow in a predetermined location, was used to measure the water status at the soil-root interface and in the bulk soil with time.