| Melatonin is one of the effective ways to alleviate the damage of adversity stress on crops. In this study, different oil sunflower varieties YE988, S2102, Longkuiza4 and Oil Supreme 909S were used as experimental materials, and four treatments of CK, K1, K2 and K3 were set up. To explore the effects of different melatonin concentrations on photosynthetic characteristics and yield of oil sunflower under compound saline-alkali stress. The results showed that compared with CK treatment, K1, K2 and K3 treatments could improve the photosynthetic characteristics of oil sunflower under saline-alkali stress, and the net photosynthetic rate increased first and then decreased at the flowering stage. YE988, S2102, Longkuiza4 and Oil Supreme 909S reached 49.38,39.47,38.64,43.16 μmol·m?2·g?1 in K2, significantly increased by 2.9%-53.9%. The yield of K2 reached 5700.77,5855.45,6005.65,6171.96kg/hm-2, respectively, which could be increased by 6.6%-22.3%. K2 treatment significantly increased net photosynthetic rate, maximum photochemical efficiency of PSII, water use efficiency and yield. In summary, spraying melatonin can alleviate the adverse effects of saline-alkali stress on photosynthesis of oil sunflower and improve the saline-alkali tolerance characteristics, and the effect is the best under 10 μmol·L-1 treatment. |