THE REDISTRIBUTION OF SOIL-WATER BY TREE ROOT SYSTEMS

Plant roots transfer water between soil layers of different water pote ntial thereby significantly affecting the distribution and availabilit y of water in the soil profile. We used a modification of the heat pul se method to measure sap flow in roots of Grevillea robusta and Eucaly ptus camaldulensis and demonstrated a redistribution of soil water fro m deeper in the profile to dry surface horizons by the root system. Th is phenomenon, termed ''hydraulic lift'' has been reported previously. However, we also demonstrated that after the surface soils were rewet ted at the break of season, water was transported by roots from the su rface to deeper soil horizons - the reverse of the ''hydraulic lift'' behaviour described for other woody species. We suggest that ''hydraul ic redistribution'' of water in tree roots is significant in maintaini ng root viability, facilitating root growth in dry soils and modifying resource availability.