EFFECT OF NITROGEN LEVEL ON PHOTOSYNTHETIC CHARACTERISTICS IN FUNCTIONAL LEAVE OF SUGAR BEET (Beta Vulgaris L.)

The effects of different nitrogen levels(0,60,120,180 and 240kg/hm2) on dynamic changes of chlorophyll content and photosynthetic characteristic of the 15th leaf(functional leaf),and on beet yield,sucrose content and sucrose yield of two sugar beet varieties(Tianyan 7 and Tianyan 8) were investigated.The results showed that: chlorophyll content,photosynthetic rate(Pn),transpiration rate(Tr) and stomatal conductance(Gs) were all expressed in single peak curve,the peak was observed on the 21st day after leaf unfolding.At the certain leaf age(21st leaf age),chlorophyll content,photosynthetic rate(Pn) increased steadily with increasing of nitrogen levels in the range of 0 ～ 120kg/hm2.Taking Tianyan 7,as an example,chlorophyll content and photosynthetic rate(Pn) were highly positive correlated to the beet yield,the correlation coefficients were R = 0.83**,R = 0.93**;and chlorophyll content and Pn were also significantly positive with the sucrose yield,the correlation coefficients were R = 0.85* and R = 0.86*.The correlation of transpiration rate(Tr) and stomatal conductance(Gs) with the sucrose content and sucrose yield were similar to photosynthetic rate(Pn).The correlation between internal CO2 concentration(Ci) and the other photosynthetic characteristics were significantly negative.On the 21st leaf age,the correlation between the chlorophyll content,photosynthetic rate(Pn) of two varieties and beet yield were significantly positive.