A COMPARISON OF PLANT HYDRAULIC CONDUCTANCES IN WHEAT AND LUPINS

Previous studies have shown similar water use for lupins (Lupinus angu stifolius 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 thro ugh the soil-plant system were measured for both species and used to c alculate the hydraulic conductance through the plant and through the r oot and shoot, The hydraulic conductance for the whole plant was 3-5 t imes greater in lupins than in wheat, This relative difference between the species was similar when plant hydraulic conductance was expresse d per unit of root length, This occurred despite the difference in mid day water potential between soil and leaves, being consistently greate r in wheat(-1.0 MPa) than in lupins (-0.7 MPa), When the total plant c onductance was separated into its components, the soil and root conduc tance and the shoot conductance were 2 and 6 times greater, respective ly, in lupins than in wheat, In the experiment under controlled condit ions, hydraulic conductance for the entire root system was determined using a pressure chamber, The specific root hydraulic conductances wer e 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 a ppreciably larger root and shoot hydraulic conductances.