Abstract:

【Objective】 In order to understand the effects of water retention agent on photosynthetic characteristics in flue-cured tobacco, diurnal changes of photosynthetic rate and its physio-ecological factors were researched under different water retention agent application rates.【Method】Diurnal changes of photosynthetic indexes were determined by the LI-6400 portable photosynthesis system. The data were analyzed by Excel2007 and SPSS13.0 with variance analysis , correlation analysis and path analysis. 【Result】 The results indicated that the net photosynthetic rates (Pn), stomatal conductance (Gs) and transpiration rates (Tr) diurnal changes in four treatments all appeared as single peak curves, the majority of peaks appeared at 9：00 or 11：00, and they all didn’t show midday depression. Overall the photosynthetic capacity of tobacco leaf gradually strengthened with water retention agent application rate growing. The net photosynthetic rate of tobacco in the control was affected by transpiration rate and atmospheric relative humidity (RH). The net photosynthetic rate of tobacco in water retention agent treatment was affected by stomatal conductance and atmospheric relative humidity. 【Conclusion】 Water retention agent could enhance the photosynthetic ability of the flue-cured tobacco leaf. When the water retention agent application rate was 45 kg•ha-1, the photosynthetic ability of the flue-cured tobacco was the strongest in four treatments. Rainy season of Yanbian provided enough water for soil which was the main cause of no midday depression phenomenon at maturing stage. Water retention agent influences the net photosynthetic rate mainly by regulating stomatal conductance (Gs) of the flue-cured tobacco.

Key words: water retention agent')">water retention agent, flue-cured tobacco, photosynthetic characteristic, diurnal changes, path analysis