| To make clear the basic characteristics of high nitrogen efficiency and its response to nitrogen fertilizer treatments as well as provide references for genetic improvement and high production and benefit cultivation, a total of18conventional indica rice varieties were potted-cultured under different nitrogen fertilizer treatments in2009and2010, respectively. The leaf area, root morphology, root activity, grain yield and yield components, dry matter weight, nitrogen ratio and nitrogen metabolism enzyme were measured. Based on nitrogen use efficiency for grain yield (NUEg) by cluster method, these rice varieties were clustered into3types in the alignment from high to low. The differences of grain yield and yield components, source-sink, dry matter production and distribution, nitrogen absorption and utilization, root traits among the indica rice varieties with different NUEg were analyzed. The main results were as follows:1. The average NUEg were44.39,49.62,53.06g.g-1(high nitrogen (N) level),53.65,62.89,74.93g.g-1(medium N level) and60.89,70.86,79.48g.g-1(Non-N level). Great differences on NUEg were detected among indica rice varieties with different NUEg and among different nitrogen fertilizer treatments. With increasing of nitrogen rate, the NUEg decreased correspondingly among rice varieties with different NUEg. The decrease range of NUEg in rice varieties with high nitrogen efficiency was lower at medium N level, while, higher at high N level.2. Great differences on grain yield were observed among indica rice varieties with different NUEg and among different nitrogen fertilizer treatments. The grain yield of rice varieties with high nitrogen efficiency was higher than that of rice varieties with medium and low nitrogen efficiency under different N level. With increasing of nitrogen rate, grain yield was increasing correspondingly.The rice varieties with high nitrogen efficiency had larger increase amplitude of grain yield than the rice varieties with medium and low nitrogen efficient. While, with further increasing of N level,the increase amplitude of grain yield became small among rice varieties with different NUEg, especially rice varieties with high nitrogen efficiency. As NUEg increased, grain yield significantly increased.Significant or highly significantly differences on panicle numbers were founded among indica rice varieties with different NUEg and among different nitrogen fertilizer treatments. The rice varieties with high nitrogen efficiency had moderate panicle numbers. Increment of panicle numbers occurred with increasing nitrogen rate among rice varieties with different NUEg. Larger increase amplitude of panicle number was detected in the rice varieties with high nitrogen efficiency than that in the rice varieties with medium and low nitrogen efficient. While, with further increase of N level, the increase amplitude of panicle numbers became small among rice varieties with different NUEg, especially rice varieties with high nitrogen efficiency. The rice varieties with high nitrogen efficiency had higher spikelets numbers than other rice types. The N level had little influence on the spikelets numbers. The grain filled percentage of rice varieties with high nitrogen efficiency was higher than that of rice varieties with medium low nitrogen efficiency under different N level.Differences of filled grain percentage were greater among rice varieties with different NUEg. Increment of filled grain percentage occurred with increasing nitrogen rate among rice varieties with high and low nitrogen efficiency. As increase of filled grain percentage, the NUEg significantly increased. The1000-filled grain weight of rice varieties with high nitrogen efficiency was relatively smaller than that of other rice types.Increase of nitrogen rate can promote the increment of1000-filled grain weight among rice varieties with different NUEg, especially on the rice varieties with high nitrogen efficiency. 3. Leaf area of rice varieties with high nitrogen efficiency was larger at heading stage and smaller at maturity stage than that of other rice types. Increase of N rate was beneficial to increasing of leaf area at heading and maturity stages. While, with further increase of N level, the increase amplitude of leaf area became small among rice varieties with different NUEg. Specific leaf weight of rice varieties with high nitrogen efficiency was small than other rice types. Increasing of N rate, the specific leaf weight showed a decreasing tendency. The rice varieties with high nitrogen efficiency had higher sink capacity than other rice types. Increase of N rate was helpful to improving of sink capacity.4. The dry matter accumulation and dry matter production of rice varieties with high nitrogen efficiency before heading and after heading was lower under nitrogen treatments. Increase of N rate was benefit to improving the dry matter accumulation and dry matter production before heading and after heading, while the increase amplitude was small in the rice varieties with high nitrogen efficiency. The economic coefficient of rice varieties with high nitrogen efficiency was significantly higher than that of rice varieties with medium and low nitrogen efficiency under different N level, especially under medium N level.The percentage of dry weight in root, stem and leaf was lower in rice varieties with high nitrogen efficiency at heading and maturity stages, the decreasing value of the percentage of dry weight in root, stem and leaf became lower at grain filling stage under nitrogen treatment. While, the percentage of dry weight in panicle was greater in rice varieties with high nitrogen efficiency at heading and maturity stages, the increasing value of the percentage of dry weight in panicle became larger at grain filling stage, especially at grain filling stage and maturity stage under nitrogen treatment. These results indicated that it was helpful to increasing dry matter in panicle at maturity by increasing nitrogen rate.5. There was no obvious tendency in the amount of nitrogen absorption at heading stage among rice varieties with different NUEg. At grain filling stage and maturity stages, the rice varieties with low nitrogen efficiency had higher amount of nitrogen absorption than other rice types. The nitrogen distribution ratio in the root, stem and leaf was lower in rice varieties with high nitrogen efficiency at heading and maturity stages than other rice types. With increasing of nitrogen rate, there existed increasing trend in the nitrogen distribution ratio in the root, stem and leaf at heading stage, while, decreasing trend at maturity under nitrogen treatments. The nitrogen distribution ratio in panicle was higher in rice varieties with high nitrogen efficiency at heading and maturity stages than other rice types, especially under nitrogen treatment. With increasing of nitrogen rate, there existed decreasing trend in the nitrogen distribution ratio in panicle at heading stage, while, increasing trend at maturity under nitrogen treatments.The amount of nitrogen translocation in root, stem and leaf was higher in rice varieties with high nitrogen efficiency at grain filling stage than other rice types, especially under nitrogen treatment. With increasing of nitrogen rate, the amount of nitrogen translocation in root, stem and leaf significantly increased. There were effective methods to improve NUEg by promoting of the amount of nitrogen translocation in root stem and leaf at grain filling stage, the decreasing of the nitrogen distribution in root, stem and leaf and improving of nitrogen distribution in panicle at maturity.6The nitrogen harvest index in the rice varieties with high nitrogen efficiency was comparatively larger than other rice types. Rational application of nitrogen fertilizer could increase nitrogen harvest index. The rice varieties with high nitrogen efficiency had higher the nitrogen physiological efficiency, nitrogen agronomic efficiency, nitrogen partial productivity than other rice types. There existed the tendency that increment of nitrogen amount might decrease the nitrogen physiological efficiency, nitrogen agronomic efficiency, nitrogen partial productivity. The nitrogen use efficiency for dry matter production (NUEd) of rice varieties with high nitrogen efficiency was higher under the medium N level and low N level than other rice types. At the high N level, the NUEd became low in the rice varieties with high nitrogen efficiency. Increment of nitrogen amount might decrease the NUEd.7.The rice varieties with high nitrogen efficiency had low root weight per plant, root absorption area per plant and root active absorption area per plant as well as medium adventitious root length per plant, adventitious root numbers per plant and root activity per plant than other rice types. Increment of N level was helpful to improving the adventitious root length per plant, adventitious root numbers per plant. Rational application of nitrogen fertilizer could increase root weight per plant, root absorption area per plant, root active absorption area per plant and root activity per plant.8.The rice varieties with high nitrogen efficiency all showed the characteristics of high grain yield under the treatments of the basic fertilizer and tillering fertilizer. The nitrogen ratio of these rice varieties at maturity was medium. The rice varieties with high nitrogen efficiency had lower amount of nitrogen absorption at the treatment of the basic fertilizer, while, higher amount of nitrogen absorption at the treatment of tillering fertilizer. The rice varieties with high nitrogen efficiency all showed the characteristics of low GS activity and higher GOGAT activity under the treatments of the basic fertilizer and tillering fertilizer. |
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