Study on the responses of wintering plants to stresses caused by acid snow

酸雨（酸雨或酸雾）是影响生态系统和农业的环境问题。酸性雪也可能是越冬植物的环境胁迫因子，因为酸性沉淀物局部集中在雪中，冰晶与芽接触的时间可能比雨中的酸性沉淀物长。以冷驯化冬小麦（Triticum aestivum L.）叶片为试材，分别进行了模拟低温下酸沉降物作为酸性雪胁迫的“平衡”和“延长”硫酸冻结试验。在pH为4.0、3.0和2.0的硫酸溶液中，采用冰植平衡法对叶片进行冷冻处理，结果表明，用pH为2.0的硫酸溶液处理的叶片存活率明显降低。在硫酸溶液（pH 2.0）中过冷至-4 ℃和-8℃后，不加冰种的叶片样品受到的伤害较小。在-4 ℃和-8℃条件下，用硫酸（pH 2.0）处理7 d，其存活率下降幅度大于清水处理。另一方面，在-4和-8℃下用硫酸（pH 2.0）长时间过冷7天对叶片样品的损害较小。结果表明，细胞外冻融过程中的酸性条件促进了小麦叶片的冻害，这是由于雪晶中的酸性物质和冻融过程中的酸性物质共同作用的结果。为了进一步了解越冬植物对酸雪胁迫的反应，人们正在研究酸雪胁迫对植物的伤害机制。

Acid precipitation (acid rain or acid mist) is an environmental problem that has affected ecosystems and agriculture. Acid snow might be also an environmental stress factor for wintering plants since acid precipitates are locally concentrated in snow and the period in which ice crystals are in contact with shoots might be longer than that of acid precipitates in rain. In this study, 'equilibrium' and 'prolonged', freezing tests with sulfuric acid, which simulate situations of temperature depression and chronic freezing at a subzero temperature with acid precipitate as acid snow stress, respectively, were carried out using leaf segments of cold-acclimated winter wheat (Triticum aestivum L.). When leaf segments were frozen in the presence of sulfuric acid solution (pH 4.0,3.0 or 2.0) by equilibrium freezing with ice-seeding, the survival rate of leaf samples treated with sulfuric acid (pH 2.0) decreased markedly. Leaf samples after supercooling to -4 and -8℃ in the presence of sulfuric acid solution (pH 2.0) without ice-seeding were less damaged. When leaf samples were subjected to prolonged freezing at -4 and -8℃ for 7 days with sulfuric acid (pH 2.0), the survival rates of leaf samples exposed to sulfuric acid decreased more than those of leaf samples treated with water. On the other hand, leaf samples were less damaged by prolonged supercooling at -4 and -8℃ for 7 days with sulfuric acid (pH 2.0). The results suggest that an acid condition in the process of extracellular freezing and/or thawing promotes freezing injury of wheat leaves, because of the combined effects of acid substances concentrated in snow crystals and freeze-thaws in an acid solution concentrated by freezing. For further characterization of the responses of wintering plants to acid-snow stress, studies on the mechanism of injury caused by acid-snow stress are in progres.