Abstract
The effects of nitrogen (N) concentration in the culture solution on the growth and dry matter production (DMP) were examined under large (14—17hPa) and small (5—8hPa) atmospheric saturation deficiency (ASD) in Japonica-type Rice Nipponbare and Indica-type Rice IR24. In Nipponbare, DMP was significantly lower in the solution with 8.0 ppm N than in the solution with 24.0 ppm N under a large ASD condition but not under a small ASD condition. In IR24, on the other hand, DMP did not differ significantly between the plants in the solutions with 24.0 and 8.0 ppm N under both ASD conditions. DMP was lower in the solution with 2.7 ppm N than in the solution with 8.0 ppm N in both cultivars under both ASD conditions, due to nitrogen deficiency. The contribution of net assimilation rate (NAR) to DMP was greater in Nipponbare than in IR24, and that of average leaf area (average LA) relative to that of NAR was greater in IR24 than in Nipponbare. In Nipponbare, the N content decreased as the N concentration in the culture solution decreased. NAR and average LA also greatly decreased accompanied with the decrease in N content under a large ASD condition, but only slightly under a small ASD condition. In IR24, on the other hand, the N content did not differ between the plants cultured in the solution with 24.0 and 8.0 ppm solutions, due to the high N absorption ability of roots, and the difference in NAR and average LA between the plants in the two solutions was slight under both ASD conditions. These mechanisms may be responsible for the difference between Nipponbare and IR24 in the response of DMP to ASD mentioned above.
