Effect of photoperiod on agronomic traits and photosynthetic physiological indexes of tobacco seedlings

<bold>Objective</bold> To investigate the effects of different photoperiod treatments on agronomic traits and photosynthetic physiological indexes of tobacco seedlings，and to provide a theoretical basis for the optimization of the light environment in the tobacco seedling stage. <bold>Method</bold> The seedlings of Zhongyan 100，K326，Yunyan 87 and CB-1 were treated with three photoperiods of 6 h，10 h and 14 h from the small cross stage to the five-leaf and one-beart stage.The experiment was conducted in a two-factor split-plot experimental design，with photoperiod treatments as the main factor and varieties as the subfactors.The entropy value method was used to analyze the photoperiod sensitivity of the agronomic traits of tobacco seedlings，to determine the chlorophyll content，and to analyze the energy distribution characteristics of PSII（photosystem II）using OJIP（fast chlorophyll fluorescence induction kinetics）curves，and to carry out the correlation analysis between the agronomic traits and photosynthesis physiological indexes. <bold>Result</bold> ①With the extension of light duration，the agronomic traits indicators of the four varieties of tobacco seedlings showed an increasing trend.②With the extension of light time，the chlorophyll content of all four varieties showed an increasing trend.③With the extension of light duration，ABS/RC（light energy absorbed per unit reaction center），TR_o/RC（energy captured per unit reaction center for reduction of primary electron acceptor QA），ET_o/RC（energy captured per unit reaction center for electron transfer），and DI_o/RC（energy dissipated per unit reaction center）of the four varieties of tobacco seedlings gradually decreased，and RS/CS_o（number of reaction centers per unit area）gradually increased，and PI_ABS（performance index based on absorbed light energy）gradually increased.④The agronomic traits of tobacco seedlings under different photoperiodic treatments showed significant positive correlations with chlorophyll content and RS/CS_o，and significant negative correlations with ET_o/RC，DI_o/RC，ABS/RC and TR_o/RC. <bold>Conclusion</bold> Under the treatment of 6-14 h of light time，the extension of light time can significantly promote the growth and photosynthesis of tobacco seedlings.Correlation analysis shows that the extended light time promotes chlorophyll synthesis and light reaction process，improves light energy utilization efficiency and promotes the growth of tobacco seedlings.