The physiology of drought resistance in the soy-bean plant (Glycine max). 1. The relationship between drought resistance and growth.
Soyabeans were grown in pots at 20, 40, 60, 80 or 100% of field capacity or were allowed to wilt 1-5 times during the growth cycle. Small decreases in soil water potential induced large increases in root:shoot ratio, but these increases were not accompanied by large reductions in total yield. Unit leaf rate [NAR] increased with increasing water stress, whereas LAR decreased. Reduced soil moisture potential resulted in leaf water deficits in the early stages of treatment and these deficits appeared to initiate modifications in root:shoot ratio. The increase in water uptake by the larger root system and the reduction in loss from the smaller shoots enabled a balance to be achieved between uptake and loss at any given soil moisture potential, so that water deficits were eliminated. It was thought that the increase in NAR could have resulted from an increase in the effective concentration of root-synthesized cytokinins reaching the shoot. It was concluded that soyabeans had a larger variety of drought-avoidance mechanisms than had previously been recorded.