Abstract: Different intensities of salt- or alkali stress were established by mixing different concentrations of NaCl and Na₂SO₄ or NaHCO₃ and Na₂CO₃, respectively, and wheatwheatgrass (Triticum aestivum L. Agropyron intermedium) seedlings were grown under the stresses for 12 days. The pH value and the Na⁺, K⁺, free Ca²⁺, Cl^-, SO₄^2-, NO₃^-, H₂PO₄-, and organic acid concentrations in the fresh shoots of stressed wheatwheatgrass seedlings were determined, aimed to approach the characteristics of pH and ion balance in wheatwheatgrass under salt- or alkali stress. The results showed that intracellular pH was relatively stable under both stresses. Cl^- concentration increased sharply and organic acid concentration changed less under increasing intensity of salt stress, while it was, in adverse under increasing intensity of alkali stress. Under both stresses, the cations in the fresh shoots were mainly Na⁺ and K⁺, but the anions were different. Under salt stress, inorganic anions were the dominant components and contributed 61.3%-66.7% to the total negative charge, while under alkali stress, the contribution of organic acid to total negative charge increased from 38.35% to 61.6% with increasing stress intensity, and became the dominant component. It was concluded that organic acid accumulation might be a key physiological response of wheat-wheatgrass for its keeping pH and ion balance under alkali stress.

Key words: transgenic crop, root exudates, crop residue, soil microorganisms, safety assessment.