Abstract:

Acid rain types in China vary gradually from sulphur-rich acid rain to nitric-rich acid rain gradually in China, however, the systematic researches on the differences of plants resistance under the varied acid rain types are still scarce. In this paper, spruce (Picea asperata) leaves were treated with both sulphur-rich acid (SRA) solution and nitric-rich acid (NRA) solution, and the damage mechanisms of cell membrane and its protective systems in leaves under the acid stresses were compared. The results showed that in a range of acidity from pH5 to pH3, the cell membrane damage and lipid-peroxidation were not remarkable. However, when the acidity of the acid solution increased to pH2.0 and pH1.0, the activities of antioxidant enzymes, chlorophyll content and membrane stability index (MSI) reduced significantly. When the acidity was as higher as pH1.0, the SOD activity reduced more sharply in the NRA stress than that in the SRA stress, while the activities of CAT and POD showed no significant changes. The results also showed that the levels of reactive oxygen species and the ehtylene-producing rate of ethylene were much higher, while the content of polyamines, chlorophyll, carotenoid, proline and soluble sugar were significantly lower under NRA stress than that under SRA stress in spruce leaves when the acidity was as high as pH1.0. These results were closely related with the fact that the oxidative ability of the dilute nitric acid is much higher than that of the dilute sulphur acid, and this difference between the two types of stress is consistent with their decline of membrane stability index (MSI) and the increment of MDA content under the same high acidity (pH2.0, pH1.0). In general in comparison with SRA stress, NRA stress had higher oxidative ability under the acidity of pH2.0 and pH1.0, the protective systems in anti-oxidative enzymes and polyamines were deteriorated more severly, thus the damage caused by NRA stress was aggravated more than SRA stress in the sprue leaves.

Key words: acid stress, nitric-rich acid, Picea asperata, cell membrane, reactive oxygen species, antioxidant systems