Effects of Nitrogen Fertilization on Chlorophyll Fluorescence Parameters of Flag Leaf and Grain Filling in Winter Wheat Suffered Waterlogging at Booting Stage

Waterlogging has great influence on yield of winter wheat in some areas of China.Nitrogen(N) application is believed to be able to improve photosynthesis of flag leaf and increase final yield.To understand the response of chlorophyll fluorescence parameters of wheat flag leaf to waterlogging stress at booting stage and the effect of N fertilization,we carried out a field experiment from autumn of 2008 to summer of 2010 using winter wheat cultivar Wanmai 54.The waterlogging stress was imposed for 7 d at booting stage.Four N treatments were designed for waterlogging stress and the control(normal watering) of which N application rate was 240 kg ha-1 in all treatments but with different proportions at land preparation,jointing,and booting stages.The results showed that the maximum chlorophyll content of flag leaves occurred at the booting stage.Under normal watering condition,Fv/Fm,Fv/Fo,and qp showed high-low variation,and the maximum values were observed between May 3 and May 11.However,under waterlogging stress at booting stage,Fv/Fm,Fv/Fo,and qp showed low-high-low curve.Compared to control treatment,waterlogging at booting stage significantly decreased Fv/Fm,Fv/Fo,qp,and ΦPSII(P0.05),and NPQ significantly increased(P0.05).With the delay of N fertilization,Fv/Fm,Fv/Fo,qp,and ΦPSII increased significantly compared to the forward N fertilization treatments.Postpone of N supply improved photosynthetic capacity by increasing photosynthetic pigment contents,and enhancing photosynthetic efficiency under water deficit.The chlorophyll content was positively correlated with Fv/Fm,qp,and ΦPSII,(P0.05),but negatively correlated relationship with NPQ(P0.01).From the chlorophyll fluorescence rapid light curves,we found that,compared to normal watering,waterlogging stress at booting stage significantly decreased the maximal relative electron transport rate(ETRmax),initial slope(α),and half saturation point of light intensity(Ek).Postpone of N fertilizer application alleviated the photodamage to PSΙΙ caused by water stress,and the compensation effect of late N fertilization occurred earlier than that of early N fertilization,which resulted in longer filling period,higher mean filling rate,and ultimately increased 1000-grain weight.