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

酸雨(酸雨或酸雾)是一个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一个环境胁迫因素，因为酸性沉淀物局部集中在雪中，冰晶与树梢接触的时间可能比雨水中的酸性沉淀物长。本研究以冷驯化冬小麦(Triticum aestivum L.)叶片为材料，进行了模拟降温条件下的平衡冻结试验和模拟酸雪胁迫条件下的低温长期冻结试验。当叶片切段在含有硫酸(pH 4.0、3.0或2.0)的溶液中冰冻时，用pH 2.0的硫酸处理的叶片样品的存活率显著下降。在无冰播的硫酸溶液中，过冷至-4和-8℃后的叶片样品受到的伤害较小。当叶片样品在-4和-8℃下用硫酸(pH 2.0)长时间冷冻7d时，硫酸处理的叶片样品的存活率比用水处理的叶片样品的降低幅度更大。另一方面，叶片样品在-4和-8℃下用pH值为2.0的硫酸持续过冷7天，对叶片的损伤较小。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，这是由于雪晶中聚集的酸性物质和冻结后浓缩的酸性溶液中的冻融共同作用的结果。为了进一步表征越冬植物对酸雪胁迫的反应，对酸雪胁迫伤害机制的研究正在进行中。

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.