Abstract:Acid deposition is among the primary environmental problems on a global basis. With the winter wheat cultivar YM 12 under field experiment subject to a range of such pollution intensities as pH = 1.5, 2.5, 3.5, 4.5 and 5.6 (the last being for CK) in the rains, we investigated their stress on nutrition qualities of grains consisting of amino acid, protein, soluble sugar, reduced sugar, starch as well as total acidity so as to provide theoretical basis for preventing and controlling the impact of acid rain on crops in China. Results suggest that for acid rain at pH ≤ 4.5 the synthesis is suppressed of total free amino acid and the inhibition is the stronger, the higher the acidity; the contents of protein (including soluble part and total) decrease progressively as a function of increasing acidity, with greater decline at pH = 1.5; at pH ≤ 4.5, the synthesis of soluble sugar is inhibited more strongly; at pH ≤ 2.5, the synthesis of reduced sugar is prevented more significantly; with the increase in acidity in the rain the total acidity and acid-sugar ratio show a tendency of first intensification and then decline, peaking at pH = 3.5; at pH ≤ 3.5 the composition of starch is greatly prevented, affecting amylopection more pronouncedly, thereby resulting in the decrease in the ratio of amylopection to amylase.