Response Mechanism Of Three Plants To Simulated Acid Rain In The Three Gorges Reservoir Area

The Three Gorges reservoir is one of the main ecological fragile and sensitive areas in the upper reaches of the Yangtze River and has a very important ecological location.In recent years,the frequency of acid rain in this area is getting higher and higher.At the same time,the reduction of total SO2 emissions and the development of transportation in the reservoir area,the NOx gas emissions from automobile exhaust emissions are increasing year by year.The sulfur-nitrogen ratio in the acid rain in the Three Gorges reservoir area has been decreasing year by year,and the Three Gorges reservoir area is facing the problem of accelerated acid rain frequency and acid rain type conversion.In this study,the photosynthetic characteristics and antioxidant enzyme activities of bamboo,Chinese fir and Cyclobalanopsis glauca under different degrees and different types of simulated acid rain stress were studied in a growing season to study the vegetation construction and acid resistance of the Three Gorges reservoir area.The cultivation of tree species provides theoretical basis and scientific basis.The main conclusions are as follows:Under acid rain stress,the malondialdehyde content and the exchangeable Al3+content of Cyclobalanopsis glauca were higher than that of bamboo and Chinese fir,while the CAT activity was lower than the other two species.The SOD activity and seedling height growth of the bamboo were higher than that of Cyclobalanopsis glauca and Chinese fir which indicated that bamboo had stronger buffer capacity against acid rain under acid rain stress and the anti-acid rain buffering capacity of Cyclobalanopsis glauca was weak.Under different acid rain concentrations,the SOD activity,POD activity,CAT activity and APX activity of the three species increased with the increase of acid rain concentration at pH)3.5,and played a protective role under acid rain stress.When acid rain concentration reached pH 2.5,SOD activity and APX activity of the three seedlings decreased,antioxidant system was damaged to a certain extent,and malondialdehyde content reached its maximum.On the other hand,the acid rain treatment at pH 4.5 promoted the synthesis of chlorophyll,the net photosynthetic rate of plants and the growth of plant height,while the net photosynthetic rate,chlorophyll synthesis,seedlings of seedlings under simulated acid rain at pH 2.5 High growth is inhibited.Under different acid rain types,the chlorophyll content of bamboo,Chinese fir and Cyclobalanopsis glauca increased with the increase of N03-concentration in acid rain,and showed the trend of NAR>MAR>SAR.The net photosynthetic rate of the three plants showed that NAR was higher than that of the other two acid rain types.The types of acid rain have little influence on the activities of antioxidant enzymes in three plants,but they also show certain regularity.When the antioxidant enzymes system has not been destroyed under mild acid rain stress,the activities of NAR-type enzymes are significantly lower than those of the other two types of acid rain,which indicates that the active oxygen produced by NAR-type acid rain is less,so the level of protective enzymes used to scavenge reactive oxygen species is lower.Under severe acid rain stress(pH 2.5),the activity of antioxidant enzymes decreased,while the activity of plant enzymes decreased slightly under NAR acid rain treatment.On the other hand,plant growth under NAR acid rain treatment was significantly higher than that under SAR and MAR acid rain treatment.Mild acid rain and the increase of NO3-concentration in acid rain can promote the growth of plant seedling height to a certain extent.The effect of acid rain on ground diameter growth of bamboo and Chinese fir is not obvious,and acid rain significantly inhibited the ground diameter growth of Cyclobalanopsis glauca.The diameter growth of Cyclobalanopsis glauca under pH4.5 treatment showed that NAR acid rain treatment is significantly greater than MAR and SAR acid rain treatment.The biomass of the three species increased with the increase of chlorophyll content,acid rain pH,acid rain NO3-,AQY,LSP and Pmax,and decreased with the increase of Rd,LCP,the four enzyme activities,malondialdehyde content and soil acidity.There was a significant negative correlation between leaf enzyme activity and acid rain pH,but not with NO3-concentration in acid rain.The concentration of NO3-in acid rain is mainly to promote the synthesis of chlorophyll content in plants.