Effects Of Acid Rain On The Physiological Characteristics Of Metasequoia Glyptostroboides

Recent years, in the southwest of China acid rain problem is appeared and becomes more and more serious with the growth of economies. The main features are high frequency, stronger acidity and heavy pollution. It results damages to plants, ecological balance, and also takes huge pecuniary loss. In this paper, the acid rain (pH2.0,3.0,4.0,5.6 (CK)) influences to the growth of Metasequoia glyptostroboides Hu et Cheng is simulated and the acid rain sensitivity of Metasequoia is described, too. It is of great meaningful for trees selecting and environmental monitoring of landscaping, and also provides the basis for relict plant protecting. The conclusions are as follows:(1) The experimental results show that the Metasequoia leaves brown spots appeared after spraying of acid rain (pH≤4.0). and with the increase in the number of acid rain spraying, spot size would be bigger and bigger, spot color would gradually deepened and new leaves was significantly higher than the old leaves in the degree of impairment.(2) Simulated acid rain exerted pressure on the growth of Metasequoia at some extent in the case of convergence of nutritional resources, light, moisture and other factors. The plant height of simulated acid rain treatments decreased more than 10% Compared with the control group and the acid treatment (pH=2.0) was particularly affected. With the treatment of acidity increased, it also showed a decreasing trend in the net photosynthetic rate, stomata conductance, intercellular CO2 concentration, transpiration rate. Possible reason was that Metasequoia adjusted to the appropriate opening stomata by sensing the environment to avoid excessive transpiration of moisture, reduce the absorption of pollutants and maintain the absorption and fixation of CO2 to adapt environmental stress.(3) The speed of Metasequoia antioxidant enzymes scavenging reactive oxygen radicals for the treatments of pH4.0 acid rain was less than the rate of MDA formation, resulting in significant accumulation of MDA; Content of various protective enzymes increased to prevent cell membrane integrity from extravasations intracellular electrolytes, the gradient under the leave of pH< 4.0 had increased in membrane permeability, membrane structure had been damaged, membrane permeability increases, it caused the cell electrolyte leakage; The amount of gradients despite the fluctuations in chlorophyll content measured under the leave of pH< 4.0 higher than those of the Metasequoia leaf chlorophyll content measured before the acid rain spraying, and always lower than the control Metasequoia leaf chlorophyll content. The acid rain could affect the content of chlorophyll of Metasequoia. It could decline the photosynthetic capacity and nutritional status. The change of chlorophyll a and b had the same trend for the total chlorophyll during the entire stress with the increase of rain intensity rising, while the chlorophyll a/b values on the whole did not change significantly, indicating similar sensitivity of chlorophyll a and b. SOD activity increased with the increase in the number of acid rain increased first and then decreased. The acid treatment (pH≤3.0) had caused too serious injuries to the Metasequoia unable to fully repair. The acid treatment (pH4.0) began to adapt treatment to actively repair the damage which caused by acid rain. POD activity in all treatments increased with the increase in the number of acid rain and then declined. It means that Metasequoia could active protection mechanism to start the enzyme activity increased sharply at the beginning of acid rain spraying, but with the increase in the number of stress, POD activity inhibited certain decreased. Metasequoia start CAT enzyme activity of protective mechanisms positively to maintain the upward trend after acid rain spraying. It means that CAT enzyme system present sensitive state after acid rain spraying.(4) In process of restoration of degraded ecosystems, the basis and prerequisite of selecting plant species is plants' resistance and ability to adapt to the environment. In this study, we preliminarily discussed the effect of acid rain on physiological characteristics of Metasequoia, and the final results show that the acid rain (pH> 4.0) can be used as acid rain damage threshold of Metasequoia. One more, Metasequoia cannot be used as landscaping and ecological restoration in polluted area because of its sensitivity to acid rain. And also, as a rare relict plant, Metasequoia should be implemented appropriate protective measures.