Physiology Mechanism Of The Nitrogen Fertilizer Regulate Spikelet Number Formation In Rice

Increasing spikelet number per panicle is one of the key factors for high yield, and panicle differentiation is the important stage for spikelet number formation. In this study, different nitrogen (N) pot experiment involving two japonica rice varieties Wuyujing3 (general rice) and 86you8 (hybrid rice) ,and different treatments were conducted. Researched young panicle growth, stem development, carbon-nitrogen metabolism of different organs in rice and illustrated that effect nitrogen fertilizer applied on spikelets number formation. Results showed as following:1. The change tendency of panicle fresh weight is "S" during the whole younger panicle initiation stage. The panicles grow slowly prophase, but grow fast markedly from spike differentiation. 86you8 and Wuyujing3 appear nitrogen fertilizer effect conversion stage of younger panicle respectively 20 days and 16 days before heading.The weigh ratio of panicle to stem at the early stage was lower and then increase gradually during younger panicle initiation stage. The weight ratio of diurnal increases of panicle to stem from 4 to 16 days before heading was correlated to the spikelet number per panicle significantly, panicle got more nutrient than internodes during this stage. The fresh weight of panicle and stem at the heading stage was correlated positively to spikelet number per panicle; and the more rapidly the panicle weight increased under enough N, the more spikelet number increased at this stage.2. The plant obtain nitrogen compound and consume non-structure carbohydrate(NSC) after applied N fertilizer from the start of panicle initiation, the N content is increased firstly and then decreased, NSC content is lower firstly and then higher in rice source and sink organs. The change tendency of different treatments was the same. Compare with different treatments, the more N applied, the more N content of organs, but NSC content was lower prophase and then increased 12 days before heading. The C/N ascend slowly with the nitrogen fertilizer level in creasing in different treatments.The N and NSC content and theirs ratio of plant 24 days before heading was two curve relation to spikelet number per panicle; and that heading stage was correlated positively to spikelet number per panicle; when N fertilizer applied feasible, the C/N of plant exceed check during 12-16 days before heading have more survived spikelets number per panicle. The NSC and N content at 24 days and 12 days before heading was parabola to spikelets number per panicle; it is the same as the plant that NSC and N content and theirs ratio before heading 24 days in sheath. The more NSC in sheath, the more spikelet number at heading stage3. The N accumulation decreased gradually during panicle initiation period, but the NSC accumulation was in opposition to N accumulation. The N accumulation of plant was highest in leaf at branch and spike differentiation stage, and NSC accumulation was highest in central sink during meiosis period. The NSC accumulation of diurnal increases of leaf from 20 to 12 days before heading was correlated to the spikelet number per panicle significantly(86you8 R=0.901*;wuyujing3R =0.927*), NSC accumulation of in central sink in this stage was also correlated to the spikelet number per panicle. The carbon-nitrogen metabolism of plant kept feasible balance state when 86you8 and wuyujing3 NSC accumulation of plant was respectively 2156.64,1668.2lmg/plant and nitrogen accumulation respectively 60.49,58.02mg/plant under nitrogen fertilizer amount respectively 120,180kg/hm^-2 in this experiment, which was in favor of increasing survived spikelets.4. The carbon-nitrogen metabolism was different with nitrogen fertilizer application time. The nitrogen metabolize of plant rapidly at branch and spikelet differentiation stage when nitrogen fertilizer applied from the start of panicle initiation, which was in favor of panicle differentiation, the more nitrogen fertilizer applied ,the little NSC of plant accumulated 32-20days before heading. The carbon metabolize of plant rapidly from meiosis on when nitrogen fertilizer applied at leaf remainder 1.5 stage, which was in favor of decreasing retrograded spikelet number, the more nitrogen fertilizer applied, the more NSC content of plant had.