To determine water uptake by rice in water-saving culture, we examined root hydraulic conductance (L0), plant growth, and root anatomy of three rice genotypes (Oryza sativa L. ssp. indica cv. Beodien, traditional upland; ssp. japonica cv. Sensho, traditional upland; ssp. japonica cv. Koshihikari, improved lowland) under three water regimes: water-saturated (hydroponic), well-irrigated aerobic (control), and water-saving aerobic in soil. In hydroponic culture, although shoot dry weight (SDW) and root number were the largest in Sensho, root L0 was the highest in Koshihikari. There was no significant relationship between root L0 and SDW in hydroponics, so root L0 might not limit shoot growth under flooding. Root L 0 was much less in soil than in hydroponics, and that of Koshihikari was the lowest, especially in water-saving conditions. Root L0 was highly correlated with SDW under water-saving conditions but not in the control, so root L0 limits shoot growth under repeated water stress. Root anatomy was less affected by water regime than root L0 and is genetically controlled. Thus, root L0 may be more affected by water channels than by root anatomy.
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