Hydraulic redistribution by two semi-arid shrub species: Implications for Sahelian agro-ecosystems |
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| Institution: | 1. University of Nottingham, Nottingham, United Kingdom;2. University of Nottingham, Sutton Bonington, United Kingdom;3. Centre for Ecology & Hydrology, Penicuik, United Kingdom;4. World Agroforestry Centre, Nairobi, Kenya;5. World Agroforestry Centre, Bamako, Mali;6. Centre for Ecology & Hydrology, Wallingford, United Kingdom;1. Institute of Environmental Engineering, ETH Zurich, 8093 Zurich, Switzerland;2. Nicholas School of the Environment, Duke University, Durham, NC 27708, USA;3. Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA;4. Pratt School of Engineering, Duke University, Durham, NC 27708, USA;5. Bordeaux Sciences Agro UMR INRA-TCEM 1220, University of Bordeaux, 33195 Gradignan, France;6. Department of Civil, Architectural and Environmental Engineering, University of Padova, via Loredan 20, 35131 Padova, Italy |
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| Abstract: | Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψs) at the 20 cm depth declined significantly during the dry season with diel changes in Ψs of −0.6 to −1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments. |
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