SOIL-PLANT WATER RELATIONS, ROOT DISTRIBUTION AND BIOMASS PARTITIONING IN LUPINUS-ALBUS L UNDER DROUGHT CONDITIONS

Lupinus albus L. from different climatic origins responded to a 15 d period of water shortage during flowering by losing 50% of the total leaf canopy and gaining 55% in stem dry weight. Water deficits also led to a significant increase in the fine root length density and a slight increase in the fine root dry weight. The latter increase was especially pronounced in the deeper soil layers. Some marginal differences among genotypes were observed in the responses. Stomatal closure by midday was an early response to water deficit, giving rise to constant predawn leaf water potentials during the first week of water shortage in spite of a decrease of 60% in the available soil water. No osmotic regulation or adjustments of the cell wall properties were observed in any of the lupin lines. We explained the maintenance of seed production in water-stressed plants by their ability to accumulate assimilates in the shoot, which would be diverted to the pods during the seed filling stage.