| This study was carried out in Yangzhou, China in 2000 and 2001, in an attempt to understand the differences of nitrogen uptake and utilization in rice and to analyze their causes, which is necessary for the improvement of nitrogen use efficiency in rice production. The recombinant inbred lines (RILs), derived from Zhenshan 97 and Minghui 63, parents of Shanyou 63 which is one of the elite Indica hybrids, were solution-cultured, 95 RILs in 2000 and 168 RILs in 2001, respectively. The traits including growth duration, plant height, nitrogen concentrations in different parts of rice plant, biomass production, grain yield, yield components and root charaters were measured for each line. The RILs were clustered into 6 types by nitrogen uptake, plant height, growth duration, sink potential, biomass production and grain yield, respectively, using hierarchical cluster method. The differences of nitrogen uptake, nitrogen use efficiency for biomass production and for grain output, nitrogen harvest index at maturity between different types of RILs were studied and causes of the differences were analyzed by investigating the relationship between nitrogen uptake and use efficiency and plant height, sink potential, growth duration, grain output and root characters at maturity. The purpose of this study is to provide valuable bases for selecting and breeding rice varieties with higher nitrogen use efficiency which is of economic and environmental importance in current rice production. Results showed as follows:1. Significant difference of nitrogen uptake at maturity between RILs was observed, with the variation of 9.66-26.3 lg/m2 in 2000 and 6.68-21.92g/m2 in 2001, respectively. The RILs with higher nitrogen uptake accumulated more nitrogen before and after heading stage while the proportion of nitrogen accumulated after heading to total nitrogen uptake was also higher. Nitrogen uptake at heading or at maturity enhanced significantly as plant height, growth duration, biomass production, sink potential and grain yield of the RILs increased. Nitrogen accumulation after heading and itsproportion to total nitrogen uptake was positively correlated to biomass, sink potential and grain yield while plant height and growth duration had no significant effect on that. Number of adventitious roots per plant, total length of adventitious roots per plant, average width of adventitious root, and root activity per plant positively affected nitrogen uptake at heading or at maturity, but the effect of root dry weight per plant on nitrogen uptake had different trends between the two experimental years.2. The range of nitrogen use efficiency for biomass production (NUEp) was 70.06-111.21 gDW/gN in 2000 and 66.00-154.35gDW/gN in 2001, respectively. NUEp was significantly correlated with nitrogen uptake and the RILs with higher nitrogen uptake at maturity had higher NUEp at heading or at maturity. As biomass production, sink potential of the RILs increased, NUEp increased but NUEp was not significantly affected by plant height and growth duration. Grain yield level also had no obvious effect on NUEp.3. Nitrogen use efficiency for grain output (NUEg) showed wide variation in the tested population, 27.21-57.83gGrain/gN in 2000 and 13.87-66.12gGrain/gN in 2001, respectively. The RILs with higher nitrogen uptake at maturity had lower NUEg. NUEg was negatively correlated with growth duration and as growth duration prolonged NUEg reduced. The effect of biomass production on NUEg was not significant. But there existed close relationship between NUEg and sink potential and grain yield. As sink potential and grain yield of the RILs increased, NUEg enhanced significantly.4. Nitrogen harvest index (NHI) varied significantly between the RILs, 39.01-73.44% in 2000 and 21.53-71.62%, respectively. The influence of plant height and biomass production on NHI was not significant. NHI was closely correlated with sink potential and NHI increased significantly with the increase of sink potential. Grain yield had a positive effect...
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