PARENT SESSION
Oral Session # 56: Plant Ecology IV: Plant - Water Relations II.
Presiding: D Rosenthal
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 200.

Hydraulic redistribution: The role of shoots.

Leffler, A. Joshua^*,1, Peek, Michael¹, Ryel, Ronald¹, Caldwell, Martyn¹, ¹ Ecology Center, Logan, Utah, USA

ABSTRACT- Hydraulic redistribution, previously termed hydraulic lift, is the movement of water from soils of high water potential to soils of low water potential through the root system of a plant. Hydraulic redistribution has been demonstrated in over 80 taxa from desert to tropical ecosystems and is thought to be a purely physical process that can occur whenever active portions of root systems are in soils of different water potential. Hydraulic redistribution likely takes place when stomata are closed and the soil-plant-air continuum is decoupled from the atmosphere. Given this, aboveground plant tissue should play little role in redistribution. To test this hypothesis, we injected a ²H label into the lower rooting zone of a Bromus tectorum (cheatgrass) monoculture and examined ²H in the upper soil. Our injections were performed twice, once in the late growing season for B. tectorum and again after the aboveground tissue was completely senesced. During both sampling periods the aboveground tissue was either left intact or removed. We found a significant difference between the water signature in upper soils collected from our deep injection plots and background samples of the soil water for both clipped and unclipped plots in the early sampling period and for the unclipped plots in the later sampling period. In the plots that differed significantly from background samples, 4 to 6% of the water in the upper soil was derived from the water we injected into the deep rooting zone. The similar fraction of upper soil water derived from the deep injections (ca. 6%) in clipped and unclipped plots during the early sampling period demonstrate that aboveground tissue is not necessary for hydraulic redistribution to occur. Although we observed lower quantities of redistributed water during the later sampling date, our data do suggest that roots of dead plants can continue to serve as conduits for water movement through the soil.

Key words: soil water dynamics, hydraulic redistribution, Bromus tectorum