Genotypic differences in root hydraulic conductance of rice (Oryza sativa L.) in response to water regimes

To determine water uptake by rice in water-saving culture, we examined root hydraulic conductance (L (0)), 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 L (0) was the highest in Koshihikari. There was no significant relationship between root L (0) and SDW in hydroponics, so root L (0) 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 L (0) was highly correlated with SDW under water-saving conditions but not in the control, so root L (0) limits shoot growth under repeated water stress. Root anatomy was less affected by water regime than root L (0) and is genetically controlled. Thus, root L (0) may be more affected by water channels than by root anatomy.