HYDRAULIC REDISTRIBUTION THROUGH THE ROOT SYSTEMS OF SENESCED PLANTS

Hydraulic redistribution, the movement of water from soil layers of higher water potential to layers of lower water potential through the root systems of plants, has been documented in many taxa worldwide. Hydraulic redistribution is influenced principally by physical properties of roots and soils, and it should occur whenever root systems span soil layers of different water potential. Therefore, hydraulic redistribution should occur through the root systems of plants with aboveground tissue removed or through the root systems of fully senesced plants as long as roots remain intact and hydrated. We examined our hypothesis in field and greenhouse studies with the annual grass Bromus tectorum . We used soil psychrometry to measure soil water potential and performed 2 H‐labeling experiments. In the field, following senescence of B. tectorum , we show substantial changes in soil water potential consistent with both upward and downward movement of water through roots. The amount of water redistributed represents a significant proportion of that which can be stored in the rooted zone. We also experimentally demonstrated upward movement of a 2 H label by roots of senesced plants and by roots of plants without aboveground tissues. In the greenhouse, we further demonstrated redistribution by senesced individuals using a 2 H label. Hydraulic redistribution through the roots of senesced plants should receive further attention because it may have important ecological consequences for soil water recharge, survival of plants through drought, and agricultural practices.