DOWNWARD FLUX OF WATER THROUGH ROOTS (IE INVERSE HYDRAULIC LIFT) IN DRY KALAHARI SANDS

Downward transport of water in roots, in the following termed ''invers e hydraulic lift,'' has previously been shown with heat flux technique s. But water flow into deeper soil layers was demonstrated in this stu dy for the first time when investigating several perennial grass speci es of the Kalahari Desert under field conditions. Deuterium labelling was used to show that water acquired by roots from moist sand in the u pper profile was transported through the root system to roots deeper i n the profile and released into the dry sand at these depths. Inverse hydraulic lift may serve as an important mechanism to facilitate root growth through the dry soil layers underlaying the upper profile where precipitation penetrates. This may allow roots to reach deep sources of moisture in water-limited ecosystems such as the Kalahari Desert.