Fundamental Characteristics Of Conventional Japonica Rice Cultivars With High Nitrogen Uptake Efficiency

The common problem in paddy field of China is the excessive usage of nitrogen fertilizer and low nitrogen utilization efficiency, which caused eutrophication and ground water pollution, meanwhile increased the cost of rice production. In light of this, improving nitrogen uptake and utilization efficiency of rice is very important for sustainable development of rice production. The increase of rice yield could be achieved by exploring genotypic variation in nitrogen uptake and utilization efficiency among rice cultivars and developing new varieties with high nitrogen uptake and utilization efficiency. Rice yield is the product of amount of nitrogen absorption (ANA) and nitrogen use efficiency for grain yield (NUEg), the increase of ANA or NUEg can improve yield, accordingly, rice cultivars with high nitrogen efficiency could be grouped into high nitrogen uptake efficiency and high nitrogen utilization efficiency. Previous reports on the relationship between nitrogen uptake and other traits usually included only a few varieties, or most of them are indica rice varieties. The genotypic variation in conventional japonica rice cultivars of different ANA types on yield and yield components, index of source and sink, dry matter accumulation and distribution, nitrogen distribution, nitrogen uptake efficiency and use efficiency and root traits are not known, and no work has been conducted on characterising traits determing high nitrogen uptake efficiency in conventional japonica rice cultivars. Some studies suggested that, plant height and growth duration have great influence on nitrogen uptake and use efficiency, but it’s not clear these two factors affect nitrogen uptake efficiency of rice cultivars with similar plant height and phenology. Ninty four conventional japonica rice cultivars were solution-cultured in2008and2009, respectively. Grain yield, dry matter weight, as well as nitrogen content in individual organs, leaf area index (LAI), sink potential, morphological and physiological traits of root were measured. The objectives of the study were to characterize the traits of japonica rice cultivars with high nitrogen uptake efficiency, in order to provide experimental evidence for genetic improvements of conventional japonica rice cultivars.122Single Segment Substitution Lines(SSSLs) were solution-cultured in2010and2011to characterize lines with different nitrogen uptake efficiency. The similarities and differences between Japonic rice cultivars and SSSLs with similar genetic background were compared on nitrogen uptake effeciency. The main results were as follows:1. There was a significant difference among all tested cultivars and lines on amount of nitrogen absorption (ANA). The range of ANA in japonica rice cultivars was16.47-48.41g·m-2(2008) and14.27～37.00g·m-2(2009), the biggest ANA was2.94and2.59times of the minimum one in2008and2009, respectively; The range of ANA in SSSLs was14.25-53.59g·m-2, the biggest ANA was3.76times of the minimum one(2009).2. There was a significant difference in plant height, growth duration and nitrogen uptake intensity among different types of cultivars and SSSLs, while the distribution of growth duration and nitrogen uptake intensity was more concentrated in SSSLs. The plant height, growth duration and nitrogen uptake intensity of high nitrogen uptake efficiency types were superior to those with low uptake efficiency. Plant height and growth duration were the main factors influencing ANA, correlation analysis and direct path analysis showed that, the influence of nitrogen uptake intensity to ANA was bigger than growth duration, especially in SSSLs.3. There was a significant difference in yield among different types of japonica rice cultivars and SSSLs. With the increase of ANA, The grain yield ofjaponica rice cultivars increased significantly, the yield of SSSLs increased first then declined. Grain yield of japonica rice cultivars was significantly related to ANA(r2008=0.8096**,r2009=0.7864**), while grain yield was significantly parabolic related to ANA(R2010=0.5916**). Enhancing ANA was beneficial to improve the grain yield of japonica rice cultivars, while the grain yield of SSSLs will decline when the ANA was too big.4. In terms of yield components, there were remarkable differences in panicle number per area and spikelet number per panicle among different uptake efficiency types of conventional japonica rice cultivars and SSSLs. Rice cultivars with high N uptake efficiency showed more panicle number per area and spikelet number per panicle than those with low N uptake efficiency. There was no significant difference in grain filling rate and1000-grain weight both of Japonic rice cultivars and SSSLs. Enhancing panicle number per area and spikelet number per panicle on stable grain filling rate and1000-grain weight, could improve the grain yield of japonica rice cultivars significantly.5. The traits of rice cultivars with high N uptake efficiency, including LAI (high effective LAI, effective LAI, total LAI) and leaf area per panicle (high effective leaf area per panicle, effective leaf area per panicle, total leaf area per panicle) at heading stage, LAI and leaf area per panicle at ripening stage, green leaf weight in heading stage, Sink potential, as well as sink potential per panicle were bigger than those with low N uptake efficiency. Grain yield per unit leaf area and net assimilation rate would declined when ANA was too big, there was no significant superiority in green leaf weight per unit leaf area among different types. The traits of SSSLs with high N uptake efficiency, including LAI at heading and ripening stage, green leaf weight in heading stage, green leaf weight per unit leaf area, Sink potential and sink potential per panicle, as well as net assimilation rate were bigger than those with low N uptake efficiency. Both the LAI and sink potential had important influence on the ANA, and the influence of sink potential was stronger than the LAI.6. There was remarkable difference in dry matter accumulation among different types of rice. Dry matter accumulation and dry matter accumulation per panicle at heading and maturity stage with high N uptake efficiency were significantly higher than those with low N uptake efficiency, while there was no significant difference in harvest index. Japonica rice cultivars of high N uptake efficiency types showed higher organic dry matter weight (root, stem, sheath and leaf, panicle) and panicle weight. SSSLs in high nitrogen uptake efficiency types showed bigger dry matter weight of root, dry matter weight of stem, sheath and leaf than other types, while dry matter weight of panicle, single panicle weight, harvest index was smaller than those in medium nitrogen uptake efficiency types. Correlation analysis and direct path analysis showed that:dry matter accumulation at maturity stage had more important effect on ANA than the harvest index. Both of dry matter accumulation before and after heading had important influence on the dry matter accumulation at maturity stage, especially the dry matter accumulation before heading. The dry matter accumulation per single panicle had more important effect on the dry matter accumulation at maturity than the panicle numbers per unit area, especially the dry matter accumulation per single panicle before heading. The improving of dry matter accumulation of leaf sheath and stem and panicle weight at maturity was beneficial to improving dry matter accumulation at maturity stage. The promotion of the dry matter accumulation per single panicle, especially the dry matter accumulation per single panicle before heading, as well as the promotion of dry matter per leaf sheath and stem heading and after heading and dry matter per panicle after heading could significantly improved the dry matter accumulation per population in the N uptake efficiency of japonica rice cultivars.7. Rice cultivars of high N uptake efficiency types had significantly higher ANA at heading stage than those with low N uptake efficiency. The ANA of organics (root, stem, sheath and leaf, panicle), ANA per panicle, population nitrogen uptake intensity and nitrogen uptake intensity per panicle of rice cultivars with high N uptake efficiency were bigger than those with low N uptake efficiency, while N content, N use efficiency for grain output, N use efficiency for dry matter production and nitrogen harvest index had no advantage. SSSLs of high nitrogen uptake efficiency types showed bigger ANA of root, ANA of stem, sheath and leaf, N content, while N use efficiency for grain output, N use efficiency for dry matter production and nitrogen harvest index were smaller. ANA of panicle of SSSLs with high nitrogen uptake efficiency was smaller than that with medium N uptake efficiency. Direct path analysis showed that:ANA before heading stage had significant effect on the total ANA than the ANA at grain filling stage; ANA of single panicle makes significant greater effect on total ANA than the panicle number; Dry matter accumulation makes significant greater effect on total ANA than N content.8. There was a significant difference in root traits among different types of japonica rice cultivars and lines. The root traits of rice cultivars with high N uptake efficiency, including root traits per plant (number of adventitious roots, root dry weight, total length of adventitious roots, total root absorptions area, root activity absorptions area, root activity per plant, the longest root length, model root length), single root traits (single adventitious root length, single adventitious root diameter), root traits per panicle (number of adventitious roots, root dry weight, root activity absorptions area per panicle), ratio of shoot to root at heading and ripening stage, were superior to those with low N uptake efficiency more or less. Weight of single adventitious root with high N uptake efficiency was smaller than that with medium N uptake efficiency, while total length of adventitious roots per panicle, total root absorption area per panicle and adventitious root diameter per panicle had no advantage. SSSLs of high nitrogen uptake efficiency types showed bigger root dry weight per plant, total length of adventitious roots per plant, total root absorptions area per plant, root activity absorptions area, the longest root length, model root length and ratio of shoot to root at heading stage, but smaller Shoot to root at ripening stage. There was no advantage in number of adventitious roots per plant and root activity per plant. Further analysis showed that, both of japonica rice cultivars and lines, high ANA could be reached by improving root dry weight per plant, ratio of shoot to root (at heading and ripening stage), number of adventitious roots per plant, Weight of single adventitious root. Root dry weight per plant, the ratio of shoot to root (at heading and ripening stage), the total length of adventitious roots per plant and dry weight per adventitious are the main factors influencing N absorptive capacity.