Toxicity of root-applied sulphite in Zea mays

Zea mays was grown in nutrient solution with different concentrations of sulphite and sulphate (0, 5, and 10 mM) at pH 5 or 7, with or without aeration, for five days. Sulphite injured the plants, especially at low pH. Lack of aeration increased the sulphite injury of the plants at the high pH. in the aerated solutions, sulphite concentrations approached zero after five hours, while the unaerated solutions still contained sulphite after four days. Very little sulphite was found in the plants. The results indicate that the toxicity to the plants of the different chemical species of the sulphite in the solution decreases in the following order: SO₂ (aq) > HSO₃ ^– > SO₃ ^2–.