Study On Screening For Rice With High Nitrogen Efficiency And Its Physiological Mechanism

This study was carried out in Sichuan Agricultural University farm in 2007 to 2009, in attempt to understand the differences of nitrogen uptake and use efficiency in rice and analyze their causes, which is necessary for the improvement of nitrogen use efficiency in rice production. The nitrogen efficiency genotype acquired can provide germplasm resources for the genetic improvement on nitrogen nutrient characteristics of rice. In this study, three parts of solution culture experiments were conducted:(1) Under the low nitrogen condition (20 mg·L-1) of rice with hydroponic, the experiment was conducted to preliminary screen for nitrogen efficiency genotype of rice from 296 varieties. (2) Under the low (20 mg·L-1) and normal (40 mg·L-1) nitrogen conditions, the experiment was conducted to identify nitrogen efficiency genotype of rice from the 26 varieties, which have been the palpable difference in nitrogen uptake and use efficiency after preliminary screen. (3) Under four nitrogen conditions (10 mg·L-1,20 mg·L-1,40 mg·L-1 and 60 mg·L-1), the experiment was conducted to analyze the physiological mechanism of different nitrogen efficiency genotypes. The main results obtained were as follows.(1)In the first experiment in 2007, the experiment was conducted to screen for nitrogen efficiency genotype of rice from 296 varieties through factor analysis. Under the low nitrogen condition (20 mg·L-1), there were significant differences in nitrogen uptake and use efficiency at tillering stage and jointing-booting stage, the maximum to minimum of nitrogen uptake efficiency was more than 10.4 times and 10.9, while the maximum to minimum of nitrogen use efficiency was more than 3.2 times and 6.8 at the two stages respectively. Because of the cumulative contribution rate of nitrogen accumulation and physiological nitrogen use efficiency with biomass was up to 93.7% and 73.7% at the two stages respectively, chose biomass for morphological indexes. At the jointing-booting stage, because of the partial correlation coefficient between the plant height and nitrogen uptake efficiency, the tillers and nitrogen use efficiency were significant, chose plant height and tillers for morphological indexes of the nitrogen uptake efficiency and nitrogen use efficiency respectively. The nitrogen accumulation, physiological nitrogen use efficiency and biomass of the nitrogen efficiency genotype were extremely significant higher than nitrogen inefficiency genotype at the two stages. The nitrogen efficiency genotype was efficient absorbing before the tillering stage and efficient utilization after the jointing stage.(2) In the second experiment in 2008, the experiment was conducted to screen for nitrogen efficiency genotype of rice from the 26 varieties, which have been the palpable difference in nitrogen uptake and use efficiency. The results indicated that, there were significant differences in nitrogen uptake and use efficiency at seedling stage to heading stage, by using nitrogen accumulation and Physiological N use efficiency for measurement indexes, the nitrogen efficiency genotype included Chaoxiandao and Meiguogu, besides the nitrogen inefficiency genotype included IR15723-45-3-2-2-1 and IR32429 through clustering analysis. The nitrogen uptake and Physiological N use efficiency of the nitrogen efficiency genotype were significant or extremely significant higher than the nitrogen inefficiency genotype at every stage. Where the nitrogen accumulation of the nitrogen efficiency genotype was 1.8-2.7 times to the nitrogen inefficiency genotype, and the nitrogen use efficiency was 1.1-1.6 times to the nitrogen inefficiency genotype. Because of the rooting ability of nitrogen efficiency genotype at the earlier growing stages, the root surface area and volume of the nitrogen efficiency genotype were significant or extremely significant more than the nitrogen inefficiency genotype at every stage. For the better root morphological characters of nitrogen efficiency genotype, it promoted nitrogen uptake and use of rice plant, by the way, it promoted growth and development of above-ground, which made the nitrogen efficiency genotype of biomass extremely significant higher than the nitrogen inefficiency genotype at every stage.(3) After the experiment of screening for nitrogen efficiency genotype, the experiment was conducted to study the difference of root morphology and physiological characteristics between nitrogen efficiency genotype (Meiguogu) and inefficiency genotype (IR3242). The results indicated that, there were significant or extremely significant differences in root total length, root surface area, root volume, and root dry weight between the two genotypes under different nitrogen treatments at different growth stages, especially in low nitrogen treatments. Because of the average lateral root length of Meiguogu was 17.85% and 17.69% higher than IR3242 at the maximum tillering stage and jointing-booting stag, the total root length, root surface area and root volume of nitrogen efficiency genotype were significant higher than inefficiency genotype in diameter classification of lmm-2mm. Keeping higher root to shoot ratio can promote nitrogen uptake of rice in order to the natural growth of shoot at the vegetative growth stages. Furthermore, the root oxidation ability of Meiguogu was significant higher than IR32429 at different stages under low nitrogen treatments, while the total absorbing surface area, active absorbing surface area, ratio of active absorbing surface area to absorbing surface area and specific surface were also significant higher than IR32429 at jointing-booting stage under different nitrogen treatments, so the root activity of nitrogen efficiency genotype was higher than inefficiency genotype.(4) Besides studying the different of root morphology and physiological characteristics, the experiment was conducted to study the difference of nitrogen metabolism and resistance physiology between the two genotypes. The results indicated that, the activity of GS, GOG AT, GDH and GPT of Meiguogu were significant higher than IR32429 at maximum tillering stage and jointing-booting stage, especially in low nitrogen treatments. So the nitrogen efficiency genotype has higher assimilation capacity to NH4+ than inefficiency genotype, which can guarantee nitrogen high use efficiency for rice. But the activity of NR of Meiguogu was significant lower than IR32429 at different stages, the result can indicate that the nitrogen efficiency genotype has higher ability of NH4+ uptake than inefficiency genotype. At the same time, the higher SPAD value and soluble sugar content of nitrogen efficiency genotype promoted the organs construction and material accumulation for the later stages. In addition, the higher capacity of SOD, POD and CAT nitrogen efficiency genotype promoted higher uptake, translocation and distribution to NH4+ and NO3- of rice, which also can improve the nitrogen use efficiency.