Uniconazole and nitrogen fertilization trigger photosynthesis and chlorophyll fluorescence, and delay leaf senescence in maize at a high population density

Reducing the leaf senescence rate could improve the grain yield in maize. In the present study, maize seeds were treated with uniconazole at concentrations of 0 and 25 mg kg-1, and nitrogen was applied at 0, 150, and 225 kg ha-1 to maize crop planted at a density of 105,000 plants ha-1. Applying uniconazole and nitrogen reduced the leaf senescence rate by increasing the leaf area per plant, chlorophyll content, net photosynthetic rate, stomatal conductance, and transpiration rate. Uniconazole and nitrogen increased the electron transport rate, photochemical quenching coefficient, variable fluorescence, maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII photochemistry. Uniconazole and nitrogen reduced the intercellular carbon dioxide concentration, nonphotochemical quenching coefficient, and malondialdehyde content but increased the soluble protein content and antioxidant enzyme activities. Applying uniconazole at a concentration of 25 mg kg-1 and nitrogen at a rate of 150 kg ha-1 obtained the maximum grain yield in maize.