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<p><span lang="EN-GB" style="font-size: 12.0pt; font-family: Garamond Premr Pro">Two neutral salts (NaCl and Na₂SO₄) and alkaline salts (NaHCO₃ and Na₂CO₃) were both mixed in 2:1 ratio, and the effects of saline and alkaline stresses on growth and physiological changes in oat seedlings were explored. Result showed that biomass, water content and chlorophyll content decreased while cell membrane permeability significantly increased under alkaline stress. Saline stress did not have obvious effect on pH value in tissue fluids of shoot and root, but alkaline stress increased pH value in root tissue fluid. The contents of Na⁺, Na⁺/K⁺, SO₄^2- increased more, and K⁺, NO₃^-,H₂PO₄^- decreased more under alkaline stress, the Cl^- content increased obviously under saline stress but had little change under alkaline stress. The increments of proline and organic acid were both greater under alkaline stress, but organic acid content kept the same level under saline stress. Alkaline stress caused more harmful effects on growth and physiological changes in oat seedlings especially broke the pH stability in root tissue fluid. Physiological adaptive mechanisms of oat seedlings under saline stress and alkaline stress were different, which mainly took the way of accumulating organic acid under alkali stress but accumulating Cl^- under saline stress.</span></p>