Responses Of Source And Sink Characteristics, Nitrogen Accumulation And Translocation To Tissue Nitrogen Concentration And Its Relationship With Nitrogen Use Efficiency In Rice

Nitrogen application rate in China has been increasing, resulting in serious environmental pollution and high production cost. Therefore, reduction of N application rate is necessary for sustainable agriculture. Achieving greater rice yields depends more on increasing nitrogen use efficiency(NUE). Breeding for high NUE variety and optimizing nitrogen management are regarded as important appaches to improve NUE and reduce environmental pollution. The present study was conducted under pot conditions using four rice genotypes with different NUE. High NUE phenotypes include Shanyou 63, Liangyoupeijiu, and R16. Low NUE phenotype is R158. The study aimed to elucidate the response of source-sink traits, yield and its components, nitrogen accumulation and translocation, nitrogen concentrations of plant parts, and to exam their relationship with NUE for grain yield(NUEg) and biomass production(NUEb). The dynamic changes in NUEb during vegetative growth stage were explored for further understanding of high NUE. For quantification of the responses, we established a linear relationship between nitrogen concentrations and NUE-related traits, which followed linear curves, i.e. y=kx+b(y stands for NUE or related traits, x is nitrogen concentration, and k is the slope and represents the degree of respone to nitrogen concentration).The main results are showed as follows:1. Plant tissues nitrogen concentration showed very close relationships with NUE, source-sink traits, yield and its components, nitrogen accumulation and translocation characteristic at panicle initiation(PI), heading(HD), and maturity(MA), respectively.(1) At the three stages, nitrogen concentration showed significantly negative correlations with NUE on the basis of grain yield(NUEg) and biomass(NUEb), but significantly positive correlations with nitrogen accumulation and translocation.(2) At the three stages, tissues nitrogen concentration showed a significantly positive correlation with biomass and panicles per plant, and had no correlation with thousand grain weight and harvest index.2. Rice genotypes with different NUE had variations in the responses of NUE to tissues nitrogen concentration at PI, HD and MA.(1) The three high-NUE genotypes(Shanyou 63, Liangyoupeijiu and R16) had much higher responses(higher slopes) of NUEb at maturity stage(MA-NUEb) to leaf and stem nitrogen concentration at PI and HD than that of low-NUE genotypes(R158). Accordingly, the high-NUE genotypes had higher MA- NUEb than that of low-NUE genotype under the same tissues nitrogen concentration at each stage.(2) The three high NUE genotypes had much higher responses(higher slopes) of NUEg response to stem and grain nitrogen concentration at MA than that of low NUE genotype. Accordingly, high-NUE genotypes had higher NUEg than that of low-NUE genotype under the same grain nitrogen concentration.3. Rice genotypes with different NUE had variations in the responses of source-sink traits to tissues nitrogen concentration at PI, HD and MA.(1) At PI, high-NUE genotypes had more positive responses in biomass, leaf dry weight and leaf area(LA) to leaf nitrogen concentration than that of low-NUE genotypes. High-NUE genotypes had higher responses than that of low-NUE genotype even at the same nitrogen concentration.(2) At HD, low-NUE genotypes had much higher responses(higher slopes) of leaf dry weight and LA response to leaf nitrogen concentration than that of high-NUE genotypes. Highand low-NUE genotype had similar responses in the leaf dry weight and LA at the same nitrogen concentration.(3) At MA, high-NUE genotypes had much higher responses(higher slopes) of grain yield to aboveground nitrogen concentration than that of low-NUE genotypes. High-NUE genotypes had more positive responses of total biomass, total spikelets and panicles per plant to aboveground nitrogen concentration, even at the same nitrogen concentration levels. Although higher yield, larger biomass, more panicles and spikelets per plant were observed in high-NUE genotypes with the similar grain nitrogen concentration, the slopes showed inconsistent relationship with NUE, depending on geneotypes.4. Rice genotypes with different NUE had variations in the responses of nitrogen accumulation and translocation to tissues nitrogen concentration at MA. High-NUE genotypes had more positive responses than that of low-NUE genotypes, even under the same aboveground nitrogen concentration levels. It indicated that high-NUE genotypes had high N caption and utilization capacity. In addition, there was no correlation between aboveground nitrogen concentration(Ab NC) and nitrogen translocation efficiency in each genotype.5. The dynamic changes in NUE during vegetative growth(20, 30, 40 day after transplanting) were observed. High-NUE genotypes showed little advantages in the NUEb than low-NUE genotype during the vegetative growth stage. Low-NUE genotype showing superiority in NUEb during vegetative growth stage may be related to more unproductive tillers with higher LA.