Effects of application nitrogen on photosynthesis and growth of different drought resistance winter wheat cultivars

The net photosynthetic rate(Pn),stomatal conductance(Gs),stomatal limited value(Ls) and aboveground biomass is at different growth stages of two contrasted drought-resistance cultivars of winter wheat treated by five nitrogen levels were investigated in field experiment.The results show that the net photosynthetic rate decreases as the plant growth,the highest Pn of the CK (no N fertilization) is on the jointing stage and those of other treatments (N fertilization) are on the tillering stage.The highest Gs and Ls of all N treatments are on the jointing stage to heading stage.They first increase and decrease finally as plant growing.Reasonable nitrogen supply can increase Pn and Gs and decrease Ls.The Pn and Gs of different cultivars are different with growth stages and nitrogen fertilizations,the Pn and Gs of dryland cultivar are higher than those of watered cultivar at the N180 treatment,and those of the dryland cultivar are higher than those of watered cultivar from the jointing stage to heading stage.The aboveground biomass increases continuously as the plant growing.The effect of nitrogen supply on the aboveground biomass is different between cultivars,which of dryland cultivar increases firstly and decreases finally as the nitrogen supply increase,and which of the watered cultivar decreases continuously.The grain yield of the two cultivars increases firstly and decreases finally with the nitrogen fertilization increase,the highest grain yield of two cultivars is on N180 treatment,so the N180 treatment is the optimize nitrogen supply level in field.