Genotypic Difference Of Nitrogen Efficiency In Rice And Its Response To Different Water And Nitrogen Management Measures

Water and nitrogen were two important factors to regulate the growth and development of rice.It was of great significance to reduce the water and fertilizer inputs and the agricultural non-point source pollution to study the relationship among rice root morphology,nitrogen uptake,material accumulation and yield formation.In this study,N high use efficiency cultivar Dexiang 4103 and Fyou 498,N low use efficiency cultivar Yixiang 3724 and Chuanyou 6203 were used as experiment material in 2015?2016,through using hydroponics and field trials,the effects of different nitrogen application patterns(SPAD diagnosis N management-N1,optimal management-N2,farmers' usual N management-N3),different irrigation methods(conventional irrigation-W1,controlled alternative irrigation-W2),as well as different fertility of soils(high fertility of soil-HFS,low fertility of soil-LFS)on rice root morphology,shoot growth,nitrogen uptake and utilization,yield formation and the relationship among them were studied.The root morphological indexes which had the greatest influence on the yield change,and the corresponding water and nitrogen optimization measures were clarified to provide theoretical basis for the synergistic enhancement of rice yield and nitrogen use efficiency.The major results were as follows:1.The yield of rice varieties with different nitrogen efficiencies was significantly different,and the high nitrogen efficiency cultivars easier to get higher grain yield because of the significant advantages in the spikelets per panicle and total spikelets,while the low nitrogen use efficiency cultivars of Chuanyou 6203 and Yixiang 3724 respectively relied on higher effective panicle number and larger 1000-grain weight to narrow the yield gap with high nitrogen use efficiency cultivars.The number of panicles and the spikelets per panicle in rice under W1 were significantly higher than under W2,and the total spikelets of rice with high N use efficiency and low N use efficiency were respectively increasd 10.75%and 4.89%than rice under W2.Grain filling of rice under W2 was better,led to greater 1000-grain weight.Among different nitrogen application patterns,rice under N3 had larger panicle number,and greater 1000-grain weight;the number of spikelets per panicle of rice under N1 and N2 patterns was higher,resulted in higher total spikelets.There were significant interaction effects between water management and nitrogen application patterns.The rice of N0 under W1 had significant advantages in total spikelets,and the yield was 1000 kg hm-2 higher than W2.While after nitrogen application,the 1000-grain weight of rice under W2 was significantly higher than under W1,as a result the yield gap between them was rapidly narrowed.Under different fertility of soils,there had little difference between N1 and N2 patterns in rice yield with high N use efficiency,and the low N use efficiency varieties showed the same trend under high soil fertility;but under the low fertility of soil,the panicle number of rice with low N use efficiency Yixiang 3724 and Chuanyou 6203 through N1 pattern were respectively reduced 8.20%and 9.83%than N2,led to a big yield gap.2.The relationship between root morphology and nitrogen accumulation(NA),nitrogen dry matter production efficiency(NDMPE),dry matter weight(DW)was close,but the regularity of this relationship was poor,the determination of the ridge regression equation of the corresponding samples in 2015 and 2016 changed greatly(0.0719?0.5449).The nitrogen absorption and utilization of different growth stages(NA,NDMPE,DW)had significant effects on the yield,but this relationship might be affected by weather conditions or species-specific,resulting in a poor regularity repetition of this relationship.The root morphological characteristics at different growth stages of rice with different N efficiency were closely related to the yield changes,and the regularity repetition of this relationship was good.The root morphological characteristics at heading stage had the highest interpretation of yield,and the coefficient of ridge regression equation was larger than 0.75.The root morphological indexes of rice with different efficiency at tillering stage,jointing stage and maturity stage both were adventitious root surface area,fine root length and adventitious root length,respectively.However,the root morphological indexes at heading stage of rice with high N use efficiency and low N use efficiency,which had the greatest effect on the yield change were coarse lateral root length and the fine root surface area,the corresponding standard regression coefficients were 0.2625-0.3618 and 0.2900?0.4317,respectively.3.The differences of root morphology between rice cultivars with different N use efficiency were not significant at tillering stage,jointing stage as well as maturity stage,but at heading stage,the root morphological indexes of high N use efficient varieties were significantly better than those of low N use efficient varieties,and it also had an obvious advantage of the root physiological activity after flowering.Under N1 and N2 patterns,the rice root at different stages growed better than other patterns,and the root physiological activities were also higher after heading stage.But the effects of this two patterns on the rice root structure was different,due to the difference of cultivar,irrigation methods as well as basic fertility of soil.Under W1,the rice with high N use efficienciey and low N use efficienciey under N1 treatment both had largest adventitious root surface area at tillering stage,the longest fine branch at jointing stage,and the longest adventitious root at the maturity stage.But under W2 and high fertility of soil,it was better to through N2 and N1 to promote the optimization of root parameters in rice with high N use efficienciey and low N use efficienciey,respectively;but under low fertility of soil,rice with high N use efficienciey and low N use efficienciey under N2 both had more reasonable root growth and distribution.Conventional irrigation coupled with SPAD diagnosis N management(nitrogen rate of 120 kg hm'2)and controlled alternative irrigation combined with optimal N management(nitrogen rate of 150 kg hm-2)were the best water and nitrogen management patterns.They could make rice with high N use efficiency and low N use efficiency have the longest.coarse lateral root length and the largest fine lateral root surface area,respectively.4.The differences of rice tiller growth and productive tiller percentage between different N use efficiency cultivars were not significant.The leaf enzymes activities at different stages of Rubisco,SS and SPS in rice with high N use efficiency were higher,the LAI was lager,led to a higher material production capacity.Rice under W2 and optimized nitrogen fertilizer(N1 and N2)had suitable rate of tillering,higher productive tiller percentage,reasonable LAI at heading stage.These manegement patterns also effective to reduce the transmittance of the population increase after heading and to decrease LAI and the enzymes activities(Rubisco,SS,SPS),led to better photosynthetic performance.However,rice under W1 and N3 patterns had higher number of ineffective tillers,lower productive tiller percentage,higher CGR at early rice growth stage,resulted in a too large population,the LAI and the activities of carbon metabolism key enzymes decreased significantly,the population photosynthetic capacity was also low.Under high fertility of soil,the trends of population aboveground growth in rice with high N use efficiency and low N use efficiency under N1 and N2 patterns were as follows:the tillers increased steadily at rice early growth stage,the number decline slowly at later growth stage,the productive tiller percentage was higher,the CGR before heading stage and the LAI were both suitable,the light transmittance of rice population was better;after heading,the LAI and activities of carbon metabolism key enzymes remained at a high level,led to a higher the population growth rate.Under low fertility of soil,the canopy characteristics and material production of high N use efficiency cultivars under N1 and N2 treatments were consistent with the trend of them under high fertility of soil.While the low N use efficiency cultivars under N1 treatment,the peak number of seedlings and panicles was less than N2,the CGR was significantly lower,the LAI of Yixiang 3724 and Chuanyou 6203 at heading stage were respectively 17.51%and 20.55%less than that of N2 pattern.The photosynthetic rate and the activities of carbon metabolism key enzymes(Rubisco?SS?SPS)in flag leaves were also lower,the photosynthetic capacity was weaker,which was not conductive to the increase of population capacity.5.Under the same water and nitrogen treatment,at elonging and heading stages,the expression of OsGS1.1,OsGS2 and OsNADH-GOGAT2 of functional leaves in rice with high N use efficiency were significantly higher,and the high N use efficiency cultivars also had stronger nitrogen absorption and utilization capacity.As a result,the amount of nitrogen absorption before anthesis and the PE were significantly higher than that of low N use efficiency cultivars,wherein the average nitrogen uptake increased from 13.72%to 37.32%at the jointing stage to heading stage.Under high fertility of soil,rice with low N use efficiency had significantl advantages in RE and AE.While under the low fertility of soil,the opposite trend was showed.Compared with W1,the gene expression of OsGS1.1,OsGS2 and OsNADH-GOGAT2 of rice function leaves under W2 treatment at the jointing and heading stages were at a higher level;the decrease of SPAD value in rice flag leaves after heading stage was significantly reduced,and it had greater advantages of NA,RE,AE and PE.The SPAD of functional leaves and nitrogen accumulation at different growth stages of rice were increased significantly with the N fertilizer application,so were the expression level of OsGS1.1,OsGS2 and OsNADH-GOGAT2 at jointing and heading.Among the three nitrogen application patterns,rice under N3 treatment always had the highest SPAD value of functional leaves as well as nitrogen uptake before jointing stage at different fertilzer of soils.However,under this pattern,the expression level of key enzymes in nitrogen metabolism was the lowest,the SPAD value of leaves decreased rapidly,and the RE,AE as well as PE were lower.Under high fertility of soil,the expression level of OsGS1.1,OsGS2 and OsNADH-GOGAT2 were higher in rice leaves under N1 and N2 paterns,the SPAD value of function leaves were also stable at a high level.N1 and N2 patterns effectively delayed the senescence of rice leaves after heading stage,promoted the nitrogen absorption and utilization after jointing stage,on the premise of ensured the optimum nitrogen uptake at jointing stage.Under low basal fertility of soil and N1 pattern,the SPAD value of function leaves in rice with low N use effieciency at different growth stages and the expression level of OsGS1.1,OsGS2,OsNADH-GOGAT2 in leaves at jointing and heading stages were less than that of N2 pattern.However,the difference of agronomic utilization rate and physiological utilization rate of rice under N1 and N2 patterns was not significant,the nitrogen recovery rate of LN1 and LN2 under N1 pattern was 13.66%and 12.06%higher than under N2 instead.