HR: 1330h
AN: H32C-0581    [PDF]
TI: The Contribution of Deep Roots to the Water Cycle: Seasonal Patterns of Water Uptake and Hydraulic Lift from Below 7 m on the Edwards Plateau, Texas USA.
AU: * McElrone, A J
EM: mcelrone@duke.edu
AF: Department of Biology Duke University, 133 BioSci Bldg., Durham, NC 27708 United States
AU: Pockman, W T
EM: pockman@unm.edu
AF: Department of Biology, University of New Mexico, Albuquerque, NM 87131 United States
AU: Jackson, R B
EM: jackson@duke.edu
AF: Department of Biology Duke University, 133 BioSci Bldg., Durham, NC 27708 United States
AU: Jackson, R B
EM: jackson@duke.edu
AF: Nicholas School of the Environment, Duke University, Durham, NC 27708 United States
AB: The presence of plant roots in deep and shallow soil is potentially important for site water balance through water uptake and redistribution between compartments. However, direct measurements of water movement through deep roots are not usually possible. We used cave systems on the Edwards Plateau in central Texas to gain access to deep roots of Juniperus ashei and Quercus fusiformis between 7 and 20 m below the soil surface. Long-term sap flux measurements of J. ashei showed that a single large root measured 7 m below the surface contributed 20 - 50% of daily transpiration, depending on the water content of surface soils. During periods without rain, upward flow through deep roots was continuous during both day and night with nocturnal hydraulic lift contributing up to 20% of daily water movement from depth. Seasonal measurements of roots of Q. fusiformis drawing upon an underground stream 20 m below the surface showed a similar pattern. In both systems, sap flux through deep roots fell to zero during the night when the water content of surface soils was high following precipitation. As surface soil water content decreased, minimum flow rate through deep roots increased steadily before dropping back to zero when surface soil water content rose following precipitation. Our results show that these large woody trees play an important role in cycling water from depth in these karst systems.
DE: 1851 Plant ecology
SC: Hydrology [H]
MN: 2003 Fall Meeting