| With the increase of population and the decrease of arable land, it has been an important way to increase crop yields and use of limited resources efficiently for the sustainable development of agriculture in China. Nitrogen plays important roles in promoting plant growth and development. Thus, selecting and breeding genotypes with high nitrogen utilization efficiency have become the main research directions to improve nitrogen utilization efficiency in rice. But in practical production, the contradiction between rice yield and nitrogen utilization was not well coordinated, and the mechanism of nitrogen absorption and utilization was even not clear. In this paper, the pot, field and hydroponics experiments were carried out on the farm of Sichuan Agricultural University, Sichuan province, China in2007to2012, by using rice genotype with high nitrogen utilization efficiency as the experimental materials, rice genotype with low nitrogen utilization efficiency as the contrast materials, which selected from296rice cultivars (Oryza sativa). The purpose of this article was to ascertain the mechanism of nitrogen efficient utilization through the analysis of nitrogen absorption, accumulation, distribution and translocation characteristics, besides propose possible control measures to synergistically improve rice yield and nitrogen utilization efficiency. The main results were as follows:(1) Rice genotype with high and low nitrogen utilization efficiency was obtained through hierarchical cluster analysis by using yield, nitrogen grain production efficiency and nitrogen harvest index as evaluation indexes. Rice genotype with high nitrogen utilization efficiency (high NUE) contains11cultivars, including Meiguogu, IR31892-100-3-3-3, IRIT216, while rice genotype with low nitrogen utilization efficiency (low NUE) contains8cultivars, including Jiazao935, IR32429. Grain yield, nitrogen utilization efficiency and nitrogen harvest index of high NUE were20.90%,14.96%and6.23%higher than those of low NUE respectively. Dry matter weight, nitrogen accumulation were significantly or extremely significantly positive correlation to grain yield, nitrogen utilization efficiency and nitrogen harvest index in jointing stage and heading stage. Therefore, matter accumulation and nitrogen absorption significantly affect rice yield and nitrogen use efficiency before heading, especially in the jointing stage and heading stage.(2) Dry matter weight and nitrogen accumulation of high NUE were significantly higher than those of low NUE in each growth stage. The peak of dry matter weight and nitrogen accumulation of high NUE appeared in heading to mature stage, and jointing to heading stage respectively, while The peak of Low NUE only appeared in tillering to jointing stage. Nitrogen accumulation rate of high NUE growth faster in the early stage, and achieved maximum in30～50d after transplanting, then slow down. Nitrogen maximum accumulation rate of Meigugu, IR31892-100-3-3-3and IRIT216calculated through second derivative method was11.32,12.36and15.83mg d-1plant-1, which was935,1.22,1.33and1.70times higher than Jiazao935,1.56,1.70and2.18times higher than IR32429of low NUE respectively. High NUE can maintain higher rate of nitrogen accumulation average duration of49days from tillering stage to heading stage, but low NUE was12days shorter than that of high NUE. Dry matter weight and nitrogen accumulation seriously affected rice yield in heading to mature stage, and the degree were62.65%,47.42%respectively. Degree of influence on nitrogen grain production efficiency were14.51%,8.77%, while degree of influence on nitrogen harvest index were22.14%,15.90%respectively.(3) Under the low nitrogen treatment, there has be significant difference in different types of root morphological characteristics between high NUE and low NUE. Fine lateral root length of high NUE is32.09%,14.66%,14.40%and12.69%higher than low NUE at seeding, tillering, jointing and heading stage, respectively. Coarse lateral root surface area of high NUE is94.70%and64.38%higher than low NUE at jointing and heading stage, while root volume is90.24%and58.18%higher. Adventitious root length, surface area and volume of high NUE is40.84%,44.90%and51.02%higher than those of low NUE at jointing stage. Root total absorbing surface area, active absorbing surface area and reducing capacity of high NUE are decreased significantly with the nitrogen treatment increase at different growth stages. Under the same nitrogen treatment, root total absorbing surface area, active absorbing surface area, oxidation ability and reducing capacity of high NUE are1.3～2.1times,1.1～3.2times,1.0～3.0times and1.4～2.2times higher than those of low NUE. Under the low nitrogen treatment, length, surface area and volume of coarse lateral root have the greatest influence on nitrogen accumulation, the influence degree is47.1%～78.4%.(4) As the main kind of organic acids of the high NUE, the secretion volume of oxalate acid accounts for more than80%of the total organic acid, and those of acetic acid and citric acid are followed. Under the same nitrogen level, the total organic acid secretion of the high NUE is significantly lower than that of the low NUE. As the main kinds of amino acid of the high NUE, the secretion volume of alanine accounts for more than50%of the total amino acid, and is followed by serine, glutamic, aspartic, phenylalanine, glycine and threonine acids. Total amino acids’ secretion and all components of amino acid secretion are decreased with the nitrogen level decrease. Under the low nitrogen levels of10and20mg L-1, the total amino acids secretion of the high NUE is significantly lower than that of the low NUE. At the tillering and jointing stages, the total organic acid and oxalate acid are significant or very significant negative correlated with the nitrogen utilization efficiency, and amino acid secretion and aspartic acid as the same.(5) High NUE was not sensitive as low NUE to nitrogen fertilizer treatment, for reducing nitrogen fertilizer that high NUE can still maintain high yield and nitrogen utilization efficiency, nitrogen recovery efficiency was especially as high as50.88%of high NUE, while low NUE was only36.44%. Nitrogen accumulation in vegetative organs of root, stem, and leaf of high NUE significantly reduced at the condition of low nitrogen level compared with normal nitrogen level, but increased by34.20%,2.51%and0.51%in panicle of high NUE in flowering, filling and mature stage, while decreased by23.47% and15.57%in panicle of low NUE in flowering, filling and mature stage respectively. Nitrogen accumulation distribution in different organs of high NUE manifested as leaf> stem> root> panicle, panicle> leaf> stem> root, panicle> stem> leaf> root in flowering, filling and mature stage respectively. With the advancement of growth period, nitrogen accumulation distribution ratio in root, stem, leaf were significantly reduced, but that in panicle increased from flowering stage (8.22%) to mature stage (65.79%). Nitrogen transfer amount in different organs of high NUE manifested as leaf> stem> root, while low NUE manifested as stem> leaf> root. Nitrogen transfer efficiency of high NUE were60.83%,60.34%under the condition of low and normal nitrogen level, which was1.67and1.55times higher than that of low NUE respectively.(6) Under the condition of field experiment, rice yield of high NUE increased significantly and then decreased with the nitrogen application levels raise, while nitrogen utilization efficiency decreased significantly only. Nitrogen recovery efficiency of high NUE was as high as45.99%, whose yield was42.51%higher than low NUE, nitrogen grain production and nitrogen recovery efficiency was1.07and1.46times higher than low NUE under low nitrogen application level of60kg hm-2. SPAD value of L3(leaf of top3) was starting to fall sharply from flowering stage under different nitrogen levels, but that of L1was starting to fall sharply only after filling stage under low nitrogen levels. Leaf SPAD value of top1fell sharply after filling stage can be characterized for nitrogen deficiency in the environment. SPAD attenuation index in leaves of high NUE manifested as L3> L2> L1under low nitrogen application level, and SPAD attenuation index reached to the highest in the filling stage. SPAD value attenuation index can reflect the nitrogen transshipment from leaves to panicle after flowering under low nitrogen application level. |
PDF Full Text Request