| N nutrition played an important role in maize yield and quality, directly regulating the process of C and N metabolism. Past study often mainly concentrated on the effect of N nutrition on the growth and development and yield of common maize, while the study of physiological indexes of C and N metabolism had seldom been released. It was the first time that special utilization spring maize varieties such as sweet maize, waxy maize, high starch maize etc., were introduced as experiment materials to study C and N metabolism. The study showed the basic principle of C and N metabolism of spring maize, and indicated the enzyme differences of C and N metabolism of different spring maize varieties, and proposed the regulation effect of different N nutrition levels on C and N metabolism and the yield and quality of spring maize. The study contributed a lot to the improvement of quality and culture with higher yield and better quality of spring maize. The main experiment results are as follows:1. The results showed that the physiological indexes of N metabolism changed with different N application rate, presenting a single peak curve at the whole growth stage with different spring maize varieties or N nutrition levels having different appearances. It also confirmed that the key enzyme activity of N metabolism of all varieties extremely significantly positively correlated with N nutrition levels. Another result was that different spring maize varieties influenced on the relation between soluble protein content and N nutrition levels.2.Physiological indexes of C metabolism showed a single curve at the whole growth stage with peak values appeared at different periods, and peak value periods influenced by different varieties and N nutrition levels. The ratio of chlorophyll a to b content didn't show orderly changes.3.Physiological indexes of C metabolism were correlated with N nutrition levels, and peak coefficient values appeared at different periods.4. Sucrose content, photosynthetic rate (PR), SPS activity in the leaf located near the ear fell gradually after silking, and SPS showed a single peak curve with different varieties and different N nutrition levels appearing differently. In general, the SS, SPS activity and PR were significantly or extremely positively correlated with sucrose content in the leaf located near the ear with the higher coefficient appearing in accordance to different varieties.5. Sucrose content in grains presented a single peak curve in the period from the 7lh day to 49lh day after silking, and the peak value appeared in different periods according to different varieties and N nutrition levels.6. Spring maize grain starch content changed as a single peak curve after silking. With N nutrition increasing in certain range, starch content increased, but decreased when N nutrition excess certain application rate. As a result, a tendency was that the higher N nutrition level was, the later peak rate of starch accumulation came. With the increasing of N application rate, the ratio of amylopectin to amylose decreased, which indicated that higher N nutrition was disadvantageous to amylopectin accumulation. The rate of protein accumulation in grains was relatively lower in the 14th day after silking, then went up from 21st day after silking, and then fell gradually after peak accumulation rate, with peak accumulation rate appearing at different periods according to different varieties and N nutrition levels.7. ADPGPase activity in spring maize grains changed as a single peak curve at filling stage, and the peak value of ADPG activity at different periods according to different N nutrition levels. ADPGPase and SS activity, PR were correlated significantly with starch content in grains, the coefficient peak values occurring in different time.8. Yield under different N application rate differed from each other extremely significantly. In the point of harvest yield, the optimal N application rate were NEAUS4 and NEAUEW at N100, NEAU248 and SIDAN19 at N200. In a word, the correlation...
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