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Title:   Author  item
                                            BLEBY, TIMOTHY - University Of Western Australiaitem
                                            McElrone, Andrewitem
                                            POCKMAN, WILLIAM - University Of New Mexicoitem
                                            JACKSON, ROBERT - Duke University
  Submitted to: Plant Cell and Environment
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/1/2010
                                    Publication  Date: 12/1/2010
                                    Citation: Bleby, T.M., Mcelrone, A.J., Pockman, W.T., Jackson, R.B. 2010. Water uptake and hydraulic redistribution across large woody root systems to 20 m depth. Plant Cell and Environment. 33(12):2132-2148.Interpretive Summary: We investigated the occurrence of hydraulic redistribution (HR) in a semi-arid woodland in central Texas to improve our understanding of the ecohydrological consequences of HR for the dominant evergreen and deciduous tree species in this water-limited ecosystem. We measured sap flow in numerous stems, lateral roots and deep roots of Quercus, Bumelia and Prosopis spp. to describe the occurrence and frequency of HR, to characterize HR patterns in relation to environmental and soil moisture conditions, and to determine the role of root size and depth. HR occurred continuously throughout the year in one form or another, even in dormant deciduous trees, indicating that patchy dry soil is a constant feature of this system and trees actively maintain roots in dry soil over long periods. We observed distinct switches in the type of HR, from steady hydraulic lift of deep water during drought to rapid redistribution of surface soil water following rain. During peak HR activity, the amount of water redistributed at night was a large proportion of daytime uptake, up to 70 % in some roots. Deep roots supplied large amounts of underground stream water during drought, but dramatically reduced their contribution following rain. Rainfall-triggered HR was complex, and the response of shallow roots to wetting and drying of topsoil was highly variable, but smaller roots were generally more dynamic than larger roots. Our results suggest that deep roots are highly responsive to surface soil moisture conditions, and they coordinate tightly with lateral roots to supply water for transpiration and HR. Overall, this study reveals strong evidence that deep-rooted woody plants are important drivers of water cycling in dry ecosystems and they can significantly influence landscape hydrology.
                                Technical Abstract: We investigated the occurrence of hydraulic redistribution (HR) in a semi-arid woodland in central Texas to improve our understanding of the ecohydrological consequences of HR for the dominant evergreen and deciduous tree species in this water-limited ecosystem. We measured sap flow in numerous stems, lateral roots and deep roots of Quercus, Bumelia and Prosopis spp. to describe the occurrence and frequency of HR, to characterize HR patterns in relation to environmental and soil moisture conditions, and to determine the role of root size and depth. HR occurred continuously throughout the year in one form or another, even in dormant deciduous trees, indicating that patchy dry soil is a constant feature of this system and trees actively maintain roots in dry soil over long periods. We observed distinct switches in the type of HR, from steady hydraulic lift of deep water during drought to rapid redistribution of surface soil water following rain. During peak HR activity, the amount of water redistributed at night was a large proportion of daytime uptake, up to 70 % in some roots. Deep roots supplied large amounts of underground stream water during drought, but dramatically reduced their contribution following rain. Rainfall-triggered HR was complex, and the response of shallow roots to wetting and drying of topsoil was highly variable, but smaller roots were generally more dynamic than larger roots. Our results suggest that deep roots are highly responsive to surface soil moisture conditions, and they coordinate tightly with lateral roots to supply water for transpiration and HR. Overall, this study reveals strong evidence that deep-rooted woody plants are important drivers of water cycling in dry ecosystems and they can significantly influence landscape hydrology.


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