Abstract: Two sorghum cultivars, one alkaline tolerant (Siza 25) and one alkaline sensitive (Longza 9), were grown in nutrient solution in a controlled environment facility. The effects of different levels of mixed alkaline (NaHCO₃∶Na₂CO₃=9∶1) stress on sorghum seedlings were assessed by measuring osmotic regulation substances and ion balance in the leaves and roots. The results showed that the concentrations of osmolytes, i.e. proline, soluble protein, soluble sugar and free amino acid, in both leaves and roots were significantly enhanced with the increase of mixed alkaline concentration and pH value. The concentrations of osmolytes increased in both leaves and roots, being higher in Siza 25 than in Longza 9 and higher in leaves than in roots. With the increase of mixed alkaline concentration, the concentration of Na⁺ in leaves and roots increased in both cultivars, but the concentrations of K⁺ and Ca²⁺ decreased. In addition, the reductions in K⁺ and Ca²⁺ concentrations were less in Siza 25 than in Longza 9. K⁺ concentration was the highest in leaves and Na⁺ concentration was the highest in roots, implying that there was a difference between the kinds and quantities of ions in balancing the osmotic potential in leaves and roots. Roots were more adversely affected by alkali stress and its ability of osmotic regulation and ion balance was weaker than leaves, suggesting that sorghum roots are more sensitive to alkali stress than its leaves.

Key words: hydrological connectivity, flow length, riparian buffer zone., vegetation pattern, scenario simulation