Researchers at Utah State University have discovered that some deep-rooted plants work during the night in order to quench their thirst the next day.

At night deep roots extract water, which leaks out of the roots in dry soil, so the plant's shallow roots can use it the next day. Researchers call the phenomenon water flux. It explains how plants such as sagebrush prosper in deserts and may be able to extract nutrients from dry soil.This type of water movement may also occur in deep-rooted crops.

"For arid-land plants in the Great Basin, it clearly improves the efficiency of extracting water from deep soil layers," said James Richards, a range scientist with the Utah Agricultural Experiment Station. When researchers prevented the water movement during the night, plants used 25 to 50 percent less water the following day.

Plants in arid regions transpire much more water than their sparse deep roots can supply. Dense shallow roots make up the deficit, using the water lost at night. At night, the difference between the water potential in the dry upper layer of soil and the deep moist soil lets plants efficiently "pull" up water.

Plants may exert some control over root water loss when conditions are extremely dry.

"Laboratory studies have shown that water leaks from roots under moderately dry conditions, but not under extremely dry conditions," Richards said.

Nighttime water flux may have advantages for nearby shallow-rooted plants such as grasses, and could affect nutrient uptake in dry soil and groundwater levels.