Effects Of Nitrogen Supply On Photosynthesis And Utilization Efficiency Of Photosynthetic Nitrogen In Flue-cured Tobacco Leaves

The utilization of nitrogen in tobacco leaves is related to photosynthesis involved light harvest,electron transfer and carboxylation Photosynthetic nitrogen utilization efficiency（PNUE,photosynthetic rates per unit nitrogen）reflects the nitrogen distribution in the photosynthetic process.Thus,this study focused on improving the photosynthetic and photosynthetic nitrogen efficiency of tobacco leaves by optimizing the nitrogen distribution in photosynthetic apparatus.In this study,solution culture experiments and open field experiments were carried out to investigate the effects of different nitrogen supply on leaf development,chlorophyll content,photosynthetic characteristics,photosynthetic nitrogen utilization efficiency,nitrogen content and proportion of different components of flue-cured tobacco in K326,NC55,Yunyan 87 and Zhongyan 100.The distribution characteristics of nitrogen in photosynthetic apparatus were estimated to clarify the mechanism of variation of photosynthesis and nitrogen use efficiency in different nitrogen supply intensities in tobacco leaves.Moreover,according to the role of chlorophyll content and component in leaf photosynthesis,the method of rapid and accurate quantitative estimation of chlorophyll content in flue-cured tobacco leaves was studied;The main results are as follows:1.Through nutrient solution experiment and field nitrogen supply experiment,the change characteristics of leaf nitrogen content and chlorophyll content,leaf photosynthetic rate characteristic parameters,chlorophyll fluorescence,CO₂ response curve of four flue-cured tobacco varieties in indoor culture and field were analyzed:（1）The net photosynthetic rate was significantly affected by the initial carboxylation efficiency,stomatal conductance and mesophyll conductance.The non-stomatal limit increased significantly in low nitrogen,which cause the photosynthetic limit increased significantly,stomatal limit was the main factor in the decrease of photosynthetic rate in high nitrogen,.（2）The net photosynthetic rate of leaves was positively correlated with the nitrogen content of carboxylation system,bioenergetics system and light harvesting system,but not with the nitrogen component.（3）The PNUE was significantly affected by leaf nitrogen components,as well as the different growth periods;the proportion of nitrogen distribution in carboxylation system,bioenergy system,photosynthetic system and non photosynthetic system determined the PNUE of flue-cured tobacco at seedling stage,while the change of photosynthetic nitrogen efficiency in field was mainly related to the nitrogen distribution in carboxylation system,bioenergy system and light harvesting system.（4）The content of chlorophyll was used as an important parameter to calculate the nitrogen component of the photosynthetic system.The photosynthetic rate of the leaf was significantly related to the nitrogen content of the photosynthetic system.The variations of PNUE were mainly caused by the nitrogen component of the photosynthetic in flue-cured tobacco of high nitrogen in the field.Also,the change of chlorophyll content affected the photosynthetic rate and PNUE of the leaf.2.The digital images of leaves were obtained from the solution culture experiments of different varieties and nitrogen supply,and the data sets of visible spectrum parameters and chlorophyll content of leaves were established.（1）The results showed that NRI,R/（G+B）,（R-B）/G,（G-R）/（R+G+B）,（R-B）/（R+G+B）,ExR and chlorophyll content were selected from 14 color indexes of normalized color index,specific color index and normalized difference color index system,which were the best candidate for color index.（2）The results showed that R/（G+B）had the highest prediction accuracy for chlorophyll content,so R/（G+B）was selected as the best color index for chlorophyll content estimation.The best prediction equations of Chl.a,Chl.b and Chl were y=-22.916x+14.353,y=-4.6338x+3.1192 and y=-27.549x+17.473,respectively.