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AGU: Water Resources Research

 

Keywords

  • hydraulic lift
  • root distribution
  • root water uptake
  • soil-plant hydrodynamics

Index Terms

  • Hydrology: Eco-hydrology
  • Hydrology: Plant uptake
  • Hydrology: Soil moisture
  • Hydrology: Vadose zone

Abstract

WATER RESOURCES RESEARCH, VOL. 44, W01432, 14 PP., 2008
doi:10.1029/2007WR006094

Onset of water stress, hysteresis in plant conductance, and hydraulic lift: Scaling soil water dynamics from millimeters to meters

Mario Siqueira

Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, USA

Departamento de Engenharia Mecânica, Universidade de Brasília, Brasilia, Brazil

Gabriel Katul

Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, USA

Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University, Durham, North Carolina, USA

Amilcare Porporato

Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, USA

Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University, Durham, North Carolina, USA

Estimation of water uptake by plants and subsequent water stress are complicated by the need to resolve the soil-plant hydrodynamics at scales ranging from millimeters to meters. Using a simplified homogenization technique, the three-dimensional (3-D) soil water movement dynamics can be reduced to solving two 1-D coupled Richards' equations, one for the radial water movement toward rootlets (mesoscale, important for diurnal cycle) and a second for vertical water motion (macroscale, relevant to interstorm timescales). This approach allows explicit simulation of known features of root uptake such as diurnal hysteresis in canopy conductance, hydraulic lift, and compensatory root water uptake during extended drying cycles. A simple scaling analysis suggests that the effectiveness of the hydraulic lift is mainly controlled by the root vertical distribution, while the soil moisture levels at which hydraulic lift is most effective is dictated by soil hydraulic properties and surrogates for atmospheric water vapor demand.

Received 6 April 2007; accepted 2 October 2007; published 25 January 2008.

Citation: Siqueira, M., G. Katul, and A. Porporato (2008), Onset of water stress, hysteresis in plant conductance, and hydraulic lift: Scaling soil water dynamics from millimeters to meters, Water Resour. Res., 44, W01432, doi:10.1029/2007WR006094.

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