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Resumption of Water Uptake by Sorghum after Water Stress

X. Xu, W. L. Bland
Agronomy journal 1993 v.85 no.3 pp. 697-702
Sorghum bicolor, water stress, duration, root systems, water uptake, transpiration, leaf water potential, soil water content, drought tolerance, dry environmental conditions, root shoot ratio, Texas
Exposure of roots to dry soil may reduce their ability to absorb water when the soil is rewet. We sought to quantify the effects of the duration of exposure to dry soil and the availability of water in deeper soil layers on resumption of water uptake by roots of Sorghum bicolor (L.) Moench following rewetting of the soil. Plants were grown in a greenhouse in pots, half of which were fitted with a water-filled reservoir below the pot bottom. Soil was allowed to dry for either 26 or 39 d before rewetting. Reservoir roots were excised at rewatering to limit uptake to roots previously exposed to soil drying. Time courses of plant transpiration and leaf water potential prior to and after rewatering were measured. Longer exposure to dry soil slowed resumption of uptake. After 26 d of drying, plants without reservoirs transpired 63.5% of that of well-watered controls without reservoirs on the first day following rewatering, compared to 29.4% following 39 d of drying. Water available below the dry soil enabled roots to resume water absorption immediately after rewatering. On the first day after rewatering following 39 d of drying, transpiration relative to well-watered controls (with and without reservoirs) was 2.6-fold greater in plants with access to a reservoir than those without. Water-stressed sorghum showed larger root/shoot and root weight/length ratios than controls.