Soil-plant water relations, root distribution and biomass partitioning in Lupinus albus L. under drought conditions

Lupinus albus L. from different climatic origins responded toa 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 fineroot length density and a slight increase in the fine root dryweight. The latter increase was especially pronounced in thedeeper soil layers. Some marginal differences among genotypeswere observed in the responses. Stomatal closure by midday wasan early response to water deficit, giving rise to constantpredawn leaf water potentials during the first week of watershortage in spite of a decrease of 60% in the available soilwater. No osmotic regulation or adjustments of the cell wallproperties were observed in any of the lupin lines. We explainedthe maintenance of seed production in water-stressed plantsby their ability to accumulate assimilates in the shoot, whichwould be diverted to the pods during the seed filling stage. Key words: Biomass partitioning, drought, Lupinus albus, root distribution, water relations.