Genotypic variation in nitrogen uptake during early growth among rice cultivars under different soil moisture regimes

In order to enhance rice productivity under water-deficient conditions, it is essential to improve nitrogen (N) uptake ability or its use efficiency. The objectives of the present study were to examine the genotypic variation in N uptake ability and physiological N use efficiency (PNUE) among 70 rice cultivars, and to clarify its association with biomass production and water uptake ability. Plants were grown under three soil moisture regimes: flooded and two non-flooded (-0.10 and -0.52 MPa soil water potential) conditions. A substantial genotypic variation in the amount of aboveground N uptake was observed, and the amount bore a positive correlation with aboveground biomass production regardless of soil moisture regime, whereas PNUE showed a negative if any correlation with biomass production depending on soil moisture regime. A significant interactive effect on the amount of aboveground N uptake between cultivars and soil moisture regimes was observed; there existed cultivars that exhibited superior N uptake only under non-flooded conditions. N uptake ability was closely correlated with water uptake ability, while a substantial genotypic variation in N uptake per unit water uptake was found in the two non-flooded regimes. These results indicate that a substantial genotypic variation in N uptake ability under water deficient conditions exists among diverse rice genetic resources, and that the variation is associated with water uptake ability and biomass production under the water-limited conditions at the early growth stage.