Trees never rest: the multiple facets of hydraulic
redistribution
Nadezhda Nadezhdina1,*, Teresa S. David2, Jorge S. David3, Maria Isabel Ferreira3, Michal
Dohnal4, Miroslav Tesař5, Karl Gartner6, Ernst Leitgeb6, Valeriy Nadezhdin1, Jan Cermak1,
Maria Soledad Jimenez7, Domingo Morales7
Ecohydrology Volume 3, Issue 4, pages 431–444, December 2010
DOI: 10.1002/eco.148
1
Institute of Forest Botany, Dendrology and Geobiocenology, Mendel University,
Zemedelska 3, 613 00 Brno, Czech Republic; 2Instituto Nacional de Recursos Biológicos,
Av. da República, Quinta do Marquês, 2780-159 Oeiras, Portugal; 3Instituto Superior de
Agronomia, Technical University of Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal;
4
Czech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7, 166 29
Prague, Czech Republic; 5Institute of Hydrodynamics of the ASCR, v.v.i., Pod Pat'ankou
30/5, 166 12 Prague, Czech Republic; 6Department of Forest Ecology and Soil, Research
and Training Centre for Forests, Natural Hazards and Landscape, Seckendorff-Gudentweg 8,
A-1131 Vienna; 7Department of Plant Biology, University of La Laguna, E-38207, La
Laguna, Tenerife, Spain
*Email: Nadezhda Nadezhdina ([email protected])
Keywords:
Vertical hydraulic redistribution; horizontal hydraulic redistribution; foliar uptake; tissue
dehydration; drought-based reversal; frost-based reversal; heat field deformation technique
Abstract
The upward movement of water due to transpiration stops when soil water potential (Ψs)
drops below leaf water potential (ΨL). Under these circumstances, water can move in any
direction in the plant-soil continuum through the passive conduits of roots and stems
towards the lowest Ψs. This is generally termed as hydraulic redistribution (HR), but the
positioning and orientation of the driving water potential gradient may vary. Any
experimental method that can measure bi-directional and low flows in the sapwood of roots
and stems will be suitable to detect HR. Using one approach for measuring sap flow (the
heat field deformation technique, HFD) in several forest species and sites across Europe, we
were able to provide evidence on different types of HR: vertical hydraulic redistribution
(VHR), horizontal hydraulic redistribution (HHR), foliar uptake (FU) and tissue dehydration
(TD). VHR is the vertical water movement through roots in response to water potential
differences between deep and topsoil, either hydraulic lift or hydraulic descent. HHR is the
lateral water movement through roots in response to horizontal water potential gradients,
namely under localised irrigation. FU is the water movement from crown to soil through
stems when the crown is wetted by foggy weather. TD is the downward movement of water
in stems or roots from above-ground tree tissues to soil under prolonged drought or frost.
Results from direct sap flow measurements indicated the vectoral and widespread nature of
HR, a phenomenon of paramount importance for overall physiology and ecohydrology.