Abstract: To clarify the alleviating roles of uniconazole as a plant growth regulator on stresses, we examined the effects of uniconazole on photosynthetic rate, intrinsic property, chlorophyll parameters, and phenotype of soybean cultivar “Kenfeng 14” under flooding stress. The results showed that flooding stress at flowering stage (R1) decreased maximum net photosynthetic rate at seedfilling stage (R6) of soybean, but had no effects on the chlorophyll contents, the maximum electron transport rate, eigenabsorption crosssection of photosynthetic pigment molecule from ground state i to excited state k as a result of light illumination, and minimum average lifetime of photosynthetic pigment molecules in the excited state. Spraying uniconazole increased the chlorophyll contents and the effective light absorption crosssection of lightharvesting pigment molecules, but decreased the minimum average lifetime of photosynthetic pigment molecules in the excited state which made more photosynthetic pigment molecules in the ground state. Compared to the floodingstressed plants received no uniconazole, spraying uniconazole increased the electron use efficiency by 45.5%, maximum net photosynthetic rate by 79.0%, and the maximum electron transport rate by 39.2%. The flooding stress decreased the chlorophyll fluorescence parameters of F_v/F_o and F_v/F_m, whose values were improved by the application of uniconazole. Both flooding stress and uniconazole treatments decreased the height, leaf area and digital biomass of soybean. However, the application of uniconazole enhanced the values of leaf hue and NDVI, and improved the growth of soybean. In conclusion, the application of uniconazole effectively alleviated the adverse impacts of flooding stress on soybean and improved the flooding tolerance of soybean.

Key words: zonal soils, inorganic nitrogen, organic nitrogen, distribution, influence factors.