Abstract: 【Objective】 The impacts of salt stress on the photosynthesis and chlorophyll fluorescence parameters of sorghum seedlings were studied for providing a foundation for sorghum cultivation, breeding and artificial regulation of salt stress.【Method】 Salt tolerant cultivar (Liaoza 15) and salt sensitive cultivar (Longza 11) were incubated in the nutrient solution at humidity of 60%, light/dark of 12 h/12 h, illumination of 134 μmol•m-2•s-1 and 28℃/25℃ of day/night. NaCl was added into the solution at 3-leaf stage and NaCl concentration levels at 0, 50, 100, 150 and 200 mmol•L-1, respectively. The response of sorghum seedlings to NaCl stress was assessed by measuring the photosynthesis and chlorophyll fluorescence parameters of seedlings. 【Result】 Low NaCl concentration (50 mmol•L-1) increased the chlorophyll content, and high NaCl concentration (100-200 mmol•L-1) reduced the content substantially. Salt stress reduced Pn, Gs, Tr, Fm, Fv/Fo, Fv/Fm, Fv′/Fm′ and qP, and increased Fo and NPQ. Low NaCl concentration (50 mmol•L-1) reduced Ci, and high NaCl concentration (100-200 mmol•L-1) increased it. The adverse impact of salt stress on Liaoza 15 was less than on Longza 11. 【Conclusion】 The small reduction in net photosynthesis rate caused by 50 mmol•L-1 NaCl stress was considered to be a result of non-stomatal restriction; but increased stomatal restriction with increased NaCl concentration resulted in more severe reductions in photosynthesis. Under salt stress, salt tolerant cultivar could protect the photosynthetic organs more effectively than salt sentitive cultivar and thus improve the production of sorghum in salt affected areas.

Key words: sorghum, salt stress, photosynthesis, chlorophyll fluorescence