Study On The Response Characteristics Of Photosynthetic Nitrogen Use Efficiency Of Indica Hybrid Rice To Different Nitrogen Application Rates

The effects of different nitrogen rates and genotypes on photosynthetic nitrogen use efficiency of rice were studied,It is an effective way to improve the nitrogen absorption efficiency of rice leaves,and then make efficient use of resources and achieve high yield of crops.Further study on the effects of different nitrogen application rates and different genotypes of rice on photosynthetic nitrogen use efficiency is an effective way to effectively improve the absorption efficiency of nitrogen nutrition by rice leaves,and then make efficient use of resources and achieve high yield of crops.A field experiment was conducted in Jiuzhou Town,Huangping County,Guizhou Province in 2019-2020 to study the response characteristics of photosynthetic nitrogen use efficiency of Indica Hybrid Rice to different nitrogen rates.In 2019,Qyou6(V1),Yixiangyou2115(V2),and in 2020,Huanghuazhan(V3)be added as the rice cultivars.Experimental details.A split-plot design with three replicates was adopted in this experiment.Cultivars(V)were assigned to the main plots,and five nitrogen rates(N0:0,N1:75 kg ha-1,N2:150 kg ha-1,N3:225 kg ha-1,and N4:300 kg ha-1)were assigned to the subplots.The main results of this experiment are as follows:1.Effects of different nitrogen application rates on photosynthetic pigment of rice leavesThe results showed that the booting,heading and maturity stage of rice increased with the increase of nitrogen application rate,that the contents of chlorophyll a,b,carotenoid increased with the increase of nitrogen application,The contents of chlorophyll a,b and carotenoid in Huanghuazhan increased at jointing and booting stage,and increased first and then decreased at heading and maturity stage.In 2019,the carotenoid content in leaves of Qyou6 was higher than that of Yixiangyou2115 13.8%.In 2020,the contents of chlorophyll a,b and carotenoid in leaves of Qyou6 at heading and mature stage were higher than those of Huanghuazhan(19.1%?23.5%?41.5%?26.0%),and the contents of carotenoid in leaves of Yixiangyou2115 at booting stage were higher than that of Qyou6 10.2%.2.Effects of different nitrogen rates on Photosynthetic Characteristics of rice leavesWwith the increase of nitrogen application rate,the leaf net photosynthetic rate(Pn),stomatal conduction to CO2(Gs)and transpiration rate(Tr)Gs at booting,heading and at maturity stage all increased first and then decreased,the intercellular CO2 concentration(Ci)at heading stage was on the contrary,Ci at booting and maturity stage showed a downward trend,while Pn and Tr at maturity stage showed an upward trend.For Huanghuazhan,Ci,Gs and Tr at jointing stage,Ci,Gs,Tr and Pn at booting and heading stage,and Gs,Tr and Pn at maturity stage showed an upward trend,Pn increased first and then decreased at jointing stage.At the same time,with the increase of nitrogen application,the maximum carboxylation rate(Vcmax),the maximum electron transfer rate(Jmax),the light compensation point(LCP)and the maximum leaf net photosynthetic rate(Pnmax)increased first and then decreased,the apparent quantum yield(AQE)increased,the light saturation point(LSP)and the dark respiration rate(Rd)decreased;The LSP,AQE and pnmax of Huanghuazhan increased first and then decreased,while Vcmax,Jmax and Rd increased,while LCP was on the contrary.In 2019,the Pnmax and Pn of Qyou6 was higher than that of Yixiangyou2115(7.59%?7.64%);in 2020,the Vcmax and Pnmax of Qyou6 were higher than that of Huanghuazhan(19.05%?17.76%),the LSP,Tr,Gs and Pn of Yixiangyou2115 was higher than that of Huanghuazhan(21.18%?9.85%?19.64%?20.92%),and the AQE of Qyou6 was higher than that of Yixiangyou2115 21.18%.3.Effects of different nitrogen application rates on leaf fluorescence characteristicsWith the increase of nitrogen application rate,at heading stage of rice the actual quantum yield of PS?(?PS?),relative electron transfer rate at PSII(ETR),Non-photochemical quenching coefficient(q N),quantum yield of regulatory energy dissipation at PSII(Y(NPQ)),quantum yield of non-regulatory energy dissipation at PSII(Y(NO)),photochemical quenching coefficient(q P),q N,Y(NPQ),at booting stage were increased Y(NPQ)and Y(NO)increased at first and then decreased at maturity,The maximal quantum yield of PS?(Fv/Fm)of PSII at booting stage and ETR at maturity stage were opposite;Fv/Fm at heading stage,?PS?,ETR and q P,at booting stage QN at maturity stage showed a downward trend,Fv/Fm and ?PS? at maturity,Y(NO)at booting stage and q P at heading stage showed an upward trend.For Huanghuazhan,ETR and Y(NO)at jointing stage,Y(NPQ)at booting stage,?PS? and q P at heading stage,q P,Y(NPQ)and Y(NO)at maturity stage all increased first and then decreased,while Y(NPQ)at jointing stage was on the contrary;Fv/Fm at jointing,booting,heading and maturity stage,ETR at booting and maturity stage,Y(NO)and Y(NPQ),Y(NO)at heading stage,at maturity stage ?PS? all showed an upward trend,however,?PS? at booting stage,q P and q N at jointing and booting stage,q N at heading and maturity stage,and ETR at heading stage showed a downward trend.In 2019,at heading stage of Yixiangyou2115 ETR was higher than that of Qyou6 48.7%.In2020,at booting stage,Fv/Fm,?PS? and ETR of Huanghuazhan were higher than those of Yixiangyou2115(7.57%?5.29%?7.96%),Y(NPQ)of Qyou6 and Yixiangyou2115 were higher than that of Huanghuazhan(24.68%?37.66%),and Y(NO)of Yixiangyou2115 was higher than that of Huanghuazhan 5.08%;at heading stage,ETR of Yixiangyou2115 was higher than that of Qyou6 11.14%;at maturity stage q N of Yixiangyou2115 and Huanghuazhan was higher than that of Qyou6(21.90%?21.14%).4.Effect of different nitrogen application on photosynthetic nitrogen utilization efficiency of rice leavesThe results showed that with the increase of nitrogen application rate,the nitrogen content per leaf area(Narea)increased at booting and maturity stage,and increased first and then decreased at heading stage;the photosynthetic nitrogen utilization efficiency(PNUE)increased first and then decreased at booting stage,on the contrary at heading stage,and increased at maturity stage.For Huanghuazhan,Narea increased at jointing and heading stage,and increased first and then decreased at booting and maturity stage,PNUE decreased at jointing,booting stage(except N0treatment)and heading stage,and decreased first and then increased at maturity stage.In 2019,the PNUE at booting stage,Narea and PNUE at heading stage were all Yixiangyou2115,higher than that of Qyou6(20.26%?13.89%?23.03%);In 2020,Narea at jointing and booting stage was Huanghuazhan,higher than Yixiangyou2115(18.19%?24.00%),PNUE at jointing and heading stage was Yixiangyou2115,higher than Huanghuazhan(26.48%?37.36%).5.Effects of different nitrogen application rates on nitrogen distribution in photosynthetic system of leavesAt heading stage,with the increase of nitrogen application rate,the yield of rice increased,the proportion of leaf N allocation to Rubisco(PR)showed a downward trend,the proportion of leaf N allocation to bioenergetic components(PB),the proportion of nitrogen distribution to light harvesting components(PL)and the proportion of nitrogen distribution in photosynthetic system(PP)showed a trend of first decreasing and then increasing.For Huanghuazhan,PR and PB showed a downward trend,while PL increased first and then decreased(except for N0 treatment),and PP was on the contrary.In 2020,the PR,PB and PP of Huanghuazhan were significantly lower than those of Qyou6(33.33%?34.07%?31.36%)and Yixiangyou2115(37.50%?33.33%?34.15%).6.The effect of different nitrogen application on nitrogen utilization rateWith the increase of nitrogen application rate,the agronomic efficiency of nitrogen fertilizer(FAE)and partial productivity of nitrogen fertilizer(PFP)of rice decreased gradually,while the absorption efficiency of nitrogen fertilizer(FRE)and physiological efficiency of nitrogen fertilizer(FPE)increased first and then decreased.For Huanghuazhan,the trend is the same.The differences among varieties were as follows: among the two varieties in 2019,FAE and PFP of Qyou6 were significantly higher than that of Yixiangyou2115(78.18%?18.68%);among the three varieties in 2020,FAE accounted for by Huanghuazhan was significantly higher than that of Qyou6 and Yixiangyou2115(68.21%?72.37%).7.Effects of different nitrogen rates on Yield and its componentsWith the increase of nitrogen application rate,the 1000 grain weight and seed setting rate of rice decreased gradually,but the effective panicle number was on the contrary,the Harvest yield increased first and then decreased,and the grain number per panicle was on the contrary.For Huanghuazhan,the number of effective panicles and grains per panicle(except N0 treatment)increased gradually,the 1000 grain weight and harvest yield increased first and then decreased,and the seed setting rate was on the contrary.In 2019,the number of grains per panicle and Harvest yield of Qyou6 were higher than those of Yixiangyou2115(24.27%?17.96%),and the1000 grain weight and seed setting rate of Yixiangyou2115 were higher than those of Qyou6(14.33%?7.65%);In 2020,the effective panicles and grains per panicle of Huanghuazhan were higher than those of Qyou6(8.08%?13.06%)and Yixiangyou2115(14.05%?20.42%),the 1000 grain weight of Yixiangyou2115 was higher than that of Qyou6 and Huanghuazhan(13.93%?34.40%),and the seed setting rate of Yixiangyou2115 and Huanghuazhan was higher than that of Qyou6(15.01%?15.96%).8.Relationship between photosynthetic nitrogen use efficiency and Related parametersIn addition,correlation analysis showed that at booting stage,photosynthetic nitrogen use efficiency of rice leaves was significantly or extremely significantly negatively correlated with ETR,and significantly or extremely significantly positively correlated with Pn,FPE,and seed setting rate;At heading stage,chlorophyll a,b,Pn,ETR,q P,Y(NO)?and effective panicle number were significantly or extremely significantly negatively correlated,while ?PS?,Fv/Fm,PL,PR,PB,PP,FAE,PFP,FRE,and 1000 grain weight were significantly or extremely significantly positively correlated;At maturity stage,Ci,q N,Y(NPQ),FRE and FPE were significantly or extremely significantly negatively correlated,while Pn,?PS?,Fv/Fm and effective panicle number were significantly or extremely significantly positively correlated.In conclusion,nitrogen nutrition plays a significant role in regulating the synthesis of photosynthetic pigments,photosynthetic function,fluorescence characteristics and the distribution of leaf nitrogen content in the photosynthetic system.There was a significant positive correlation between nitrogen supply level and photosynthetic pigment content,Moderate application of nitrogen fertilizer can improve the self-protection energy of functional leaves in rice,the opening degree of the PSII reaction center,and enhance the electron flow of the PSII reaction center lateral to the oxidation of PSII,thereby improving the PSII electron transport capacity,ultimately contributing to the improvement of the PSII quantum yield,to improve the efficiency of light energy conversion inside the leaf,and at the same time,it is beneficial to increase the stomatal conductance,increase the rate of transpiration,promote the opening of leaf stomata,increase the photosynthetic rate,and promote leaf uptake of CO2 to participate in photosynthesis.In this study,we further confirmed that Harvest yield was greatly affected by the number of available panicles and grain number per panicle,as well as confirmed that differences in leaf nitrogen content in photosynthetic system allocation were important factors affecting photosynthetic nitrogen use efficiency in rice leaves.