A comparison of plant hydraulic conductances in wheat and lupins

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Abstract
Previous studies have shown similar water use for lupins (Lupinus angustifolius L.) and wheat (Triticum aestivum L.), despite a considerably smaller root system in lupins. A field study and an experiment under controlled conditions using pressure-flux relationships were conducted to examine whether higher hydraulic conductances were responsible for the greater water uptake per unit root length in lupins. In the field experiment, the flux of water and differences in water potential through the soil-plant system were measured for both species and used to calculate the hydraulic conductance through the plant and through the root and shoot. The hydraulic conductance for the whole plant was 3–5 times greater in lupins than in wheat. This relative difference between the species was similar when plant hydraulic conductance was expressed per unit of root length. This occurred despite the difference in midday water potential between soil and leaves, being consistently greater in wheat (−1.0 MPa) than in lupins (−0.7 MPa). When the total plant conductance was separated into its components, the combined soil and root conductance and the shoot conductance were 2 and 6 times greater, respectively, in lupins than in wheat. In the experiment under controlled conditions, hydraulic conductance for the entire root system was determined using a pressure chamber. The specific root hydraulic conductances were 4 times greater in lupins than in wheat. The results from both field and controlled conditions experiments suggest that the greater water uptake per unit root length in lupins compared to wheat results from appreciably larger root and shoot hydraulic conductances.

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