An international team of researchers led by a University of California, Davis, soil scientist has for the first time demonstrated that the soil around plant roots contains more water than does soil in other areas.

The findings, which contradict earlier beliefs that soil in the immediate vicinity of the roots has less water, could potentially lead to development of more drought-tolerant plants and more efficient irrigation systems.

The results of the study appear in the October issue of the scientific journal New Phytologist.

“Plants take water up from the ground by means of fine roots, a few millimeters in diameter,” said Ahmad Moradi, a postdoctoral fellow in the UC Davis Department of Land, Air and Water Resources. “Their thicker roots serve more as pipelines, to relay the water. We want to understand the water distribution around these fine roots because this is the place where the roots remove water from their surrounding soil.”

At the Paul Scherrer Institute in Switzerland, the researchers used a method known as neutron tomography to create a precise three-dimensional image of water distribution around the plant roots and in other soil areas. This technology allowed them to show the distribution of water to a fraction of a millimeter, without having to remove a plant from the soil.

“Neutrons are sensitive to water, and plant roots consist of around 90 percent water,” Moradi said. “When one wants to examine them, or the movement of water in the soil, neutrons are far better tools than X-rays.”

“It is probable that a gel-like substance that the roots exude is responsible,” said Andrea Carminati, a co-author at the University of Göttingen, Germany. “This substance can absorb 10,000 times its own dry weight of water. In this way, plants could create an emergency supply for short periods.”

In addition to Moradi and Carminati, the research team included Eberhard Lehmann of the Paul Scherrer Institute, Switzerland; Sascha Oswald of the University of Potsdam, Germany; and Hans-Jörg Vogel of the Helmholtz-Centre for Environmental Research, Germany.

Funding for the study was provided by the European Union Marie Curie Water Watch Project.