Abstract:

To investigate the effects of varying nitrogen(N)application rates on carbon and nitrogen metabolism and the formation of yield and quality in sugar beet,a field experiment was conducted at the Science and Technology Park of Inner Mongolia Agricultural University,Hohhot,Inner Mongolia Autonomous Region.Five N application treatments were implemented with rates of 0(N0),60(N60),120(N120),180(N180),240 kg/ha (N240).Dynamic changes in the main photosynthetic physiological indices,along with key enzymes and products involved in carbon and nitrogen metabolism of sugar beet,were analyzed under different treatments throughout its entire growth stage.The results showed that nitrogen application exerted significantly different effects on the photosynthetic characteristics,activities of key carbon and nitrogen metabolic enzymes and their metabolic products in sugar beet across different growth stages.In terms of photosynthetic characteristics,the SPAD values of all N-applied treatments on June 17 and July 2 were 10.06%—32.45%,4.19%—26.98% higher than those of N0,respectively.The N180 treatment showed the highest SPAD value and Fv/Fm on August 20,and exhibited relatively high SPAD values and Fv/Fm on September 20.Regarding the activities of key carbon and nitrogen metabolic enzymes,the N180 treatment exhibited the highest activities of sucrose phosphate synthase(SPS),sucrose synthase(SS),nitrate reductase(NR),and glutamine synthetase(GS)on July 17,which were 17.20%,20.37%,18.39%,31.30% higher than those of N0,respectively.In addition,the SPS activity on September 20 and SS activity on August 5 in the N180 treatment were also the highest,reaching 15.51,21.59 μg/(g·min),respectively.Regarding carbon and nitrogen metabolites,with the progression of the growth period,the soluble sugar content in taproots and the total nitrogen content in leaves both exhibited an overall increasing trend.The N180 treatment exhibited the highest total nitrogen content in both leaves and taproots on August 5,and the highest soluble sugar content in leaves on September 20.In terms of yield and quality,with the increase in nitrogen application rate,taproot yield showed an overall increasing trend,while sugar content exhibited an overall decreasing trend.Under the N180 treatment,the taproot yield reached 106.46 t/ha(31.00% higher than N0),the sugar content was 13.43%(0.63 percentage points lower than N0),and the sugar yield was the highest at 14.30 t/ha(25.11% higher than N0).Correlation analysis indicated that the activities of key enzymes(SPS,SS)of carbon metabolism were positively correlated with sugar yield,and carbon metabolites were negatively correlated with sugar yield overall.The activities of key enzymes(NR,GS)of nitrogen metabolism were positively correlated with sugar yield,and the total nitrogen content of taproots was positively correlated with sugar yield overall.In conclusion,a nitrogen application rate of 180 kg/ha optimized the photosynthetic performance of sugar beet leaves,promoted the coordination of carbon and nitrogen metabolism in leaves and taproots,balanced taproot yield and sugar content,and thus increased sugar yield.

Key words: Sugar beet, Nitrogen application, Photosynthetic performance, Carbon metabolism, Nitrogen metabolism, Sugar yield

CLC Number: 

• S566.3

• S143.1氮肥