Mechanism Of Differences In Nitrogen Fertilizer Production Efficiency Among Different Wheat Genotypes

The experiments were carried out to study the differences of root characteristics, N accumulation and distribution in plants, grain protein accumulation, grain starch accumulation among wheat genotypes with different nitrogen fertilizer production efficiency (NPE) in Jiangsu Provincial Key Lab of Crop Genetics and Physiology from 2004 to 2006, in order to definitude the mechanism of differences in nitrogen fertilizer producition efficiency among different wheat genotypes. The effects of N application amount and N forms on root characteristics, N accumulation and distribution in plants, grain protein accumulation, grain starch accumulation among wheat genotypes with different N efficiency were studied to definitude the regulation effects of N application amount and N forms on NPE, explore the regulation approaches of coordinating grain yield, quality and N efficiency. The main results were as follows.1. Differences in NPE among different wheat genotypesNPE were different among different wheat genotypes, and the variation range of NPE were different under different N application amount and different N forms. NPE were reduced with higher N application amount. The order of NPE among three N form treatments was CONH2—N>NO3-—N>NH4+—N. The effects of N application amount and N forms on NPE were significant, so the order of different wheat varieties in NPE was probably different with different N appliaction amount or different N forms.2. Relationship between N distribution in plants and NPEDynamics of N accumulation amount in plants were nearly the same in different wheat varieties under different N application. N accumulation amount in plants increased gradually and reached the maxium at maturity. And N accumulation amount during the period of elongation stage to anthesis was greatest. N accumulation amount had no significant correlations with NPE, but the ratio of grain accumulation amount to plant accumulation amount had significant correlations with NPE.The ratio of grain accumulation amount to plant accumulation amount in wheat with high NPE was greater than that in wheat with low NPE. The translation ability of nitrogen from vegetative organs to grains in wheat varieties with high NPE was stronger than that in wheat varieties with low NPE. When N application amount was increased to 300 kg/hm2 from 150 kg/hm2 , the decrease degree of NPE in wheat varieties with high NPE was greater than that in wheat varieties with low NPE. Wheat varieties with high NPE needed to decrease N application amount, while wheat varieties with low NPE needed to increase N application amount. Effects of N forms on the ratio of grain accumulation amount to plant accumulation amount were nearly the same with the effects of N forms on NPE. So the ratio of grain accumulation amount to plant accumulation amount was one of the important factors affecting NPE.3. Relationship between N absorption amount for producing 100㎏ grain and NPEN absorption amount for producing 100㎏ grain (NAAP100) in wheat varieties with low NPE was higher than that with high NPE. When N application amount was increased to 300㎏/hm2 from 150㎏/hm2, NAAP100did not significantlyincrease in Qinmai11 while that increased significantly in Yangnong 9817, which resulted in a greater decrease in NPE in Yangnong 9817. Under every N forms, NAAP100 in Qinmai11 with low NPE was higher than that in Yangnong9817 with high NPE. NAAP100 in NO3-—N treatment was the lowest among N form treatments, so the NPE in NO3-—N treatment was the highest in Qinmai11, while NAAP100 in NO3-—N treatment was the highest among N form treatments, therefore, the NPE in NO3-—N treatment was the lowest in Yangnong9817. So, NAAP100 was also one of important factors affecting NPE.4. Relationship between root characteristics and NPEChanges of root characteristics in different wheat varieties under different N application amount and different N forms were studied. The changes of root volume and dry weight showed a single peak curve, and root volume and dry weight reached their peaks at booting stage. The daily increase rate of root volume and dry weight rose slowly at 5-leaf stage, increased rapidly after elongation stage, reached their maximum at booting stage. The changes of root absorbing area, actively absorbing area and root activity increased before booting stage, but decreased after booting stage.The decrease degree of root characteristics in wheat varieties with low NPE was greater than that in wheat varieties with high NPE during the late growth period. When N application amount was increased from 150 to 300㎏/hm2, the decrease degree of root absorption ability became larger in wheat varieties with high NPE, so, the decrease degree of NPE in wheat varieties with high NPE was greater than that in wheat varieties with low NPE. It suggested that the decrease rate of root characteristics during the late growth period could be one of factors affecting NPE.The effects of N forms on root volume, root dry weight, root absorbing area, actively absorbing area and root activity were nearly the same with the effects of N forms on N accumulation amount at maturity.5. Relationship between grain protein and starch accumulation and NPEThe result indicated that grain protein content was negatively correlated with NPE, while grain amylose, amylopectin and starch contents were positively correlated with NPE. The activities of NR, GS, GOGAT in flag leaves and GS, GOGAT, GPT in grains had positive correlations with grain protein and its component contents in wheat varieties with different NPE. The activities of AGPP, SSS and GBSS per grain had positive correlations with amylose, amylopectin and starch accumulation amount per grain, and the activities of AGPP, SSS and GBSS per unit grain weight had positive correlations with grain amylose, amylopectin and starch contents.Because the criteria of grain protein content among varieties for different end uses were different, not only the effects of N fertilizer on yield and NPE, but also the effects of N fertilizer on grain protein content should be considered. Grain protein content in CONH2—N treatment in strong-gluten wheat varieties was the highest among N form treatments, and could meet the national standards for strong-gluten wheat (GB/T17892—1999), so CONH2—N should be the first choice for strong-gluten wheat production .While grain protein content in NH4+—N treatment in weak-gluten wheat varieties was the lowest among N form treatments, and could meet the national standards for weak-gluten (GB/T17893—1999), so NH4+—N should be the first choice for weak -gluten wheat production . Grain protein content in NH4+—N treatment in medium-gluten wheat varieties was the highest among N form treatments, so NH4+—N should be the first choice for medium-gluten wheat production.