Effects of different nitrogen application rates on chlorophyll fluorescence parameters of tobacco leaves under condition of not uncovering plastic film.

Under the condition of not uncovering the plastic film in the whole growth and developmental period of flue-cured tobacco in field,the effects of different nitrogen application rates on the photosynthesis and chlorophyll fluorescence parameters of tobacco leaves were studied.The results showed that the photosynthetic rate,stomatal conductance and transpiration rate of tobacco leaves increased with the increase of nitrogen application rate.Not uncovering the plastic film could reduce fertilizer loss caused by high rainfall,but the chlorophyll fluorescence parameters indicated the growth of flue-cured tobacco was stressed by not uncovering the plastic film.When the application rate of nitrogen fertilizer increased,the PSⅡ maximum photochemical efficiency Fv/Fm and Fv/Fo values increased,the photochemical quenching coefficient qP relevant to the absorbability of leaf to the light energy decreased,the variable fluorescence non-photochemical quenching coefficient qNP increased,and the apparent photosynthetic electron transport rate ETR and PSⅡ actual photochemical efficiency ΦPSⅡ both decreased.