Effects of Nitrogen Application on Chlorophyll Fluorescence Characteristics of Middle Leaves at Topping Stage in Flue-Cured Tobacco

Field experiment was carried out to study effects of different nitrogen application rates on chlorophyll fluorescence characteristics such as photochemical efficiencies, photosystem II efficiencies and fluorescence quenching efficiencies of middle tobacco leaves at the topping stage. Four levels of nitrogen fertilizer(0, 60, 120 and 180 kg/hm2) were applied in field experiment. The results showed that PSII actual photochemical efficiency( ΦPSII), photosynthetic electron transport rate( ETR) and photochemical quenching( q P) were significantl y( P0.05) increased with higher application rates of nitrogen fertilizer. When applying N 0~180kg/hm2 in the field experiment, maximum fluorescence(Fm), variable fluorescence(Fv) and maximum quantum efficiency(Fv/Fm)were significantly decreased, otherwise, non-photochemical quenching(NPQ) significantly increased. Based on this study, an optimum nitrogen rate was conducive to ensure strong photosynthetic capacity of middle leaves at late growth stage in flue-cured tobacco.