Abstract: In order to develop methods for bioremediation of acid soils,hydroxyl release from roots of wheat seedlings in a hydroponic experiment as affected by form of nitrogen fertilizer under acidic conditions was investigated with an automatic titration system.Results show that pH of the nutrient solutions,4.0 in initial pH and 15:1,3:1 and 1:1 in NO₃^-/NH₄⁺  molar ratio separately,increased after 6 days of wheat culturing.The higher the molar ratio,the greater the increase in solution pH.Correspondingly,the absorption of nitrate by wheat and the release of hydroxyl from wheat roots also increased with the rising molar ratio.These findings suggest that the preferential absorption of nitrate by wheat and subsequent release of hydroxyl from wheat roots cause increase in solution pH.In solutions the same in NO₃^-/NH₄⁺ molar ratio,being 3:1,and varied in initial pH,the increases in solution pH and hydroxyl release followed the order of:initial pH 4.0>initial pH 4.5>initial pH 5.0,suggesting that lower pH condition favors nitrate uptake by wheat and hydroxyl release from wheat roots.A 10-hour pH-stat experiment shows that wheat roots released more hydroxyl under pH-stat conditions than under non-pH-stat conditions.The higher the molar ratio,the greater the difference.It is,therefore,feasible to develop a new method for bioremediation of acid soil based on the preference of wheat to absorb nitrate and release hydroxyl from roots under acidic conditions,that is to say,to increase the release of hydroxyl by regulating nitrate content in the soil and hence to increase soil pH.

Key words: wheat, NO₃^-/NH₄⁺ molar ratio, hydroxyl release, soil acidification, bioremediation method