Abstract: To clarify the effects of different salt stress conditions on the growth and function of photosynthetic apparatus in Sorghum bicolor seedlings, we evaluated the influences of different Na⁺ concentrations of two neutral salts (NaCl and Na₂SO₄) and two alkaline salts (NaHCO₃ and Na₂CO₃) on the seedling growth and functions of photosystem Ⅰ (PSⅠ) and photosystem Ⅱ (PSⅡ) in sorghum variety “Longza No. 17” using hydroponics and simulated salt stress method. The results showed that all the four salt stresses at different concentrations inhibited the growth of sorghum seedlings. The inhibitory effect of the two alkaline salts, especially Na₂CO₃, was significantly stronger than that of both neutral salts. The neutral salt NaCl had the lowest effect on the growth of sorghum seedlings. The PSⅡ activity in the leaves of sorghum seedlings was inhibited and the maximum PSⅠ redox potential (△I/I_o) decreased under all salt stress conditions. The decrease in PSⅡ activity was mainly reflected by the reduction in the activity of oxygen-evolving complex (OEC) on the donor side of PSⅡ and the blockage of electron transfer from Q_A to Q_B on the receptor side of PSⅡ. Especially, the donor side was more sensitive to salt stress than the receptor side of PSⅡ. In addition, under the four salt stress conditions, the ability of PSⅡ reaction center to harvest and utilize light was reduced, as well as the concentration of reaction centers (expressed as per unit leaf area) and the ratio of excitation energy to absorb energy. The absorbed- light energy of PSⅡ reaction center was mainly dissipated in the form of heat energy. The effects of the four salt stress conditions on the growth and function of photosynthetic apparatus were in order as follows: Na₂CO₃>NaHCO₃>Na₂SO₄>NaCl. Therefore, in addition to salt damage, the influence of total alkalinity and the degree of alkalization should be considered while planting sorghum in saline and alkali soils.

Key words: Artemisia ordosica, soil water, rainfall pulse, infiltration characteristics