Water Relations and Osmotic Adjustment of Leaves and Roots of Lupins in Response to Water Deficits 1

Increasingly, lupins ( Lupinus spp.) are being grown as a dryland crop in marginal rainfall areas, yet their water relations characteristics and adaptation to water deficits are largely undescribed. The present study was initiated to determine the waterelations and degree of osmotic adjustment in leaves and roots of lupins in the greenhouse and in the field. Four experiments were conducted. In the first two, the leaf water relations of Lupinus angustifolius and L. cosentinii were compared. The results showed the L. angustifolius leaves were morelastic and had a higher osmotic pressure under adequately watered conditions, but the degree of osmotic adjustment to a slowly imposed water deficit was negligible in L. angustifolius and about 0.2 MPa in L. cosentlnii . In the third experiment, the waterelations and osmotic adjustment of leaves and roots of five lupin species/cultivars were compared at a predawn leaf water potential of ‒ 1.6 MPa. Leaf elasticity in general was not influenced by water deficits. In the leaves, osmotic adjustment varied among species; L. pilosus and L. atlanticus had the greatest degree of osmotic adjustment (0.4–0.5 MPa) and L. augustifolius the least (0.1 MPa). The increases in osmotic pressure arising from a water deficit were paralleled by decreases in the turgid weight/dry weight ratio. In this greenhouse experiment, no osmotic adjustment was observed in the roots of any of the species. In the fourth experiment, conducted in the field, the leaves of L. angustifolius adjusted osmotically by 0.2 to 0.3 MPa and roots by about 0.4 MPa. The osmotic adjustment in both leaves and roots was accompanied by a decrease in the turgid weight/dry weight ratio. The data suggest that changes in turgid weight/dry weight ratio may provide a simple screening method for osmotic adjustment in Lupinus .