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Biology of Dryland Plants

Pockman, William [1], McElrone, Andrew [2], Jackson, Robert [3].

Structure and function of the deep roots of woody species on the Edwards Plateau, Texas, USA.

Many woody species produce deep roots but direct measurements of deep root function at depth are rare. We used caves on the Edwards Plateau in central Texas to study the distribution and function of deep roots (7 - 22 m). All of the dominant trees in the region produce roots more than 5 m below the surface and the dominant Quercus fusiformis produces roots as deep as 22 m below the surface. We used Granier and Heat Ratio sap flow methods to assess the dynamics of water transport through deep roots and the main stem of Q. fusiformis and Juniperus ashei at two sites. In both species, flow through deep roots varied considerably in response to environmental conditions on the surface. Over short time periods, deep root flow was tightly coupled with fluctuations in canopy transpiration as light conditions varied. Over longer time periods deep root flow, and in particular minimum nighttime flow, varied with water content of surface soils. Immediately following precipitation, when shallow soils were wet, minimum nighttime flow through deep roots fell to near zero soon after canopy transpiration ceased. In contrast, minimum nighttime flow increased as surface soils dried, resulting in constant upward flow through deep roots during intervals between precipitation events. The change in nighttime deep root flow with soil drying suggested that upward hydraulic redistribution (hydraulic lift) was occurring and this was confirmed by measurements of reverse flow in shallow roots of J. ashei. Nighttime transpiration and refilling of stem capacitance were negligible or a small component of nocturnal deep root flow. Thus, in these systems deep roots provide access to more reliable water supplies and represent an avenue for redistributing that water during drought.

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1 - University of New Mexico, Department of Biology, Msc03 2020, Albuquerque, New Mexico, 87131-1091, USA
2 - St. Joseph\'s University, Department of Biology, 5600 City Ave, Philadelphia, Pennsylvania, 19131, USA
3 - Duke University, Dept of Biology and Nicholas School of the Environment and Earth Sciences, Box 90340, Durham, North Carolina, 27708-0340, USA

water relations
rooting depth
Hydraulic redistribution
hydraulic conductance
Sap flow.

Presentation Type: Symposium or Colloquium Presentation
Session: 41-3
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 8:30 AM
Abstract ID:342

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