| Nitrogen is one of the many nutrient elements necessary for plant growth and development,and plays an important role in controlling maize(Zea mays L.)yield and quality.The current use of nitrogen fertilizer efficiency is low;this resulting in increased production costs,and brings environmental pollution and other issues.Therefore,the selection of nitrogen efficient varieties,reasonable fertilization,improve crop nitrogen use efficiency is of great significance.The experiment was carried out in two parts.The first part was divided into two groups: the total nitrogen content,the nitrogen uptake rate,the nitrogen use efficiency and the nitrogen use efficiency.The results showed that under the heading of 200 kg·ha-1.Dry matter production efficiency as screening index,cluster analysis,divided into three categories: I low nitrogen efficient type,II low nitrogen medium effect type,III low nitrogen inefficient type.The second part of the field experiment,respectively,Zhengdan 958,Jiulong 5 and Suiyu 7 selected from the three types as the test materials,set six levels of nitrogen supply,0,100,140,180,220 and 260 kg/ha(N0,N1,N2,N3,N4 and N5,respectively),and their yield,photosynthetic characteristics,nitrogen metabolism related enzymes and nitrogen uptake,assimilation,accumulation and the difference of nitrogen use efficiency and its response to nitrogen were used to elucidate the reason of the difference in nitrogen utilization efficiency of different nitrogen efficiency maize varieties.The results of pot experiment showed that low nitrogen and high efficiency(I),low nitrogen medium(II)and low nitrogen inefficiency(III)accounting for 12.5%,37.5% and 50.0% respectively.The varieties of type I were significantly higher than other varieties.The correlation analysis showed that the dry matter production efficiency of nitrogen was positively correlated with total dry weight,total nitrogen content and nitrogen uptake rate,and positively correlated with nitrogen use efficiency.Path analysis showed that nitrogen dry matter production efficiency and total Dry weight was significantly related to the total dry weight of nitrogen dry matter production efficiency contribution.The results showed that under different nitrogen supply levels,dry matter accumulation,nitrogen use efficiency,yield,aboveground and grain nitrogen accumulation,nitrogen transport efficiency,nitrogen contribution to grain,net photosynthetic rate,photosynthetic key Enzymes including Ru BP carboxylase and PEP carboxylase and leaf nitrogen metabolism related enzymes include nitrate reductase,nitrite reductase,glutamine synthetase and glutamate synthetase activity and nitrogen uptake,assimilation,accumulation and so on For the low nitrogen and high efficiency varieties Zhengdan 958 was significantly higher than the low nitrogen medium varieties Jiulong 5 and low nitrogen and low efficiency varieties Suiyu 7.Dry matter accumulation is gradually increasing with the progress of fertility.The physiological indexes of photosynthetic characteristics showed a single peak curve during the five growing periods of self-extracting,tasselling,silking,grain filling and maturing stages,and all of them reached the lowest point at maturity.The peak time varies depending on the variety and nitrogen nutrition level.It is important to maintain high photosynthetic performance at later growth stage to increase the material production and yield formation during grain filling stage.During the growth period,the photosynthetic performance and dry matter accumulation of Zhengdan 958 were significantly higher than those of Xinxin No.1 and Suiyu 7.With the increase of nitrogen supply level,the photosynthetic capacity and dry matter accumulation in Zhengdan 958 were as follows: N3>N4>N5>N2>N1>N0,which was expressed as N4>N3>N5>N2>N1>N0 in Jiulong 5,and performance as N4>N5>N3>N2>N1>N0 in the Suiyu 7.The physiological indexes of nitrogen metabolism change with different nitrogen supply levels.The physiological indexes of nitrogen metabolism showed a single peak curve during the growth period,tasselling period,silking period and grain filling stage.However,the different nitrogen application levels of different varieties were inconsistent.Compared with Xinxin No.1 and Suiyu 7,the peak of nitrogen metabolism related enzymes in Zhengdan 958 was later,and the higher nitrogen metabolism related enzymes were beneficial to the nitrogen absorption and material production at later growth stage.In the period of growth period,the activities of nitrogen metabolism related enzymes were expressed as follows: N3>N4>N5>N2>N1>N0 in Zhengdan 958,which was expressed in Jiulong 5 and Suiyu 7: N4>N5>N3>N2>N1>N0.With the increase of nitrogen supply level,the nitrogen content of leaves and stems of Zhengdan 958 and Xinxin No.1 increased first and then decreased,and Suiyu 7 showed a trend of increasing.While the nitrogen transport efficiency and the nitrogen contribution to the grain of the three varieties showed a tendency to increase first and then decrease.Compared with Xinxin No.1 and Suiyu 7,Zhengdan 958 had higher nitrogen content,nitrogen translocation efficiency and nitrogen contribution rate of leaf and stem at the supply level.The low nitrogen and high efficiency cultivar Zhengdan 958 has higher yield and nitrogen use efficiency because of its high photosynthetic characteristics and activities of nitrogen metabolism related enzymes thanthat in low nitrogen medium effect cultivar Jiulong 5 and low nitrogen low efficiency cultivar Suiyu 7,thus promoting the accumulation of plant material and nitrogen absorption and assimilation,so that the use of nitrogen metabolism to improve the efficiency of higher yields.Low nitrogen and low efficiency varieties are more sensitive to nitrogen fertilizer,but their nitrogen use and utilization ability is lower. |
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