| Guangxi is one of the regions with serious acid rain pollution,where are many mountains and basins.Its climate is humid,the air pollutant diffusion ability is relatively poor,often cause serious acid rain harm.Acid rain has a lot of adverse effects on the growth,and lead to the damage of plant membrane system and the disturbance of plant physiological metabolism.Alnoides(Betula Betula)is a kind of excellent native tree species in the tropical and subtropical regions of China,which is characterized by fast growth,strong resistance,high quality and high value.Study on the growth and physiological changes of the Alnoides under the action of acid rain is of great significance to the cultivation and promotion of the Guangxi and other areas.In this study,1 year old.Betula alnoides seedlings as the research object,set the pH 2.0,pH 3.0,pH 4.0,pH 5.0,pH 5.6 five simulated acid rain concentration,using pH 6.0 as control,seedlings growth and leaf chlorophyll contents,gas exchange parameters,osmotic adjustment,cell the membrane permeability and antioxidant system were studied.The main results are as follows:1.The seedlings of Betula Betula did not show any serious symptoms under the simulated acid rain.With the decrease of pH value of simulated acid rain,seedling height and relative growth rate,biomass,root shoot ratio decreased,and the decrease amplitude is increasing;the diameter and relative growth rate,aboveground biomass,total biomass decreased first and then increased and then decreased.Under simulated acid rain pH 5.6 treatment,seedling height and relative growth rate,aboveground biomass,underground biomass,total biomass,root shoot ratio were the largest,respectively 7.91%,3.97,0.82 g/strains,4.79 g/strains,0.21,but the difference was not significant with the control.2.With the decrease of pH value of simulated acid rain,the content of chlorophyll a,stomatal conductance decreased;chlorophyll b content,chlorophyll content,net photosynthetic rate,intercellular CO2 concentration and transpiration rate increased first and then decreased;chlorophyll a/b decreased first and then increased and then decreased.Under simulated acid rain pH 5.6 treatment,the content of chlorophyll a,chlorophyll a/b reached the maximum,respectively 6.18 mg/g and 2.38,there were significant differences with the control.In simulated acid rain solution of pH 5.0,the content of chlorophyll b,total chlorophyll content was significantly higher than that of other treatments.Under simulated acid rain treatments,the net photosynthetic rate,stomatal conductance,intercellular CO2 concentration and transpiration rate were significantly lower than the control;Under simulated acid rain pH 4.0 treatment,the transpiration rate was maximum,which was 0.37 mmol/(m2·s),there was no significant difference with the control.The effects of simulated acid rain on stomatal conductance of the leaves were higher than that of net photosynthetic rate,intercellular CO2 concentration and transpiration rate.There was a significant positive correlation between the relative growth of seedling height,underground biomass,root shoot ratio and chlorophyll a content,total chlorophyll content,chlorophyll a/b,net photosynthetic rate,stomatal conductance,intercellular CO2 concentration;and there was a significant positive correlation between relative biomass,aboveground biomass,total biomass and chlorophyll a/b,net photosynthetic rate,stomatal conductance and intercellular CO2 concentration.3.Under the simulated acid rain treatment,Alnoides seedling leaves soluble protein content was significantly lower than that of control.With the decrease of pH value of simulated acid rain,soluble sugar content and soluble protein content increased first and then decreased;proline content generally showed an increasing trend,and the increase is larger.Under simulated acid rain pH 4.0 treatment,soluble sugar content was maximum,was 81.70 mg/g,and little difference with the control;the proline content of simulated acid rain of pH 2.0 was 3.07 ?g/g,was significantly higher than that of control and other treatment of simulated acid rain.There was a significant negative correlation between free proline content and seedling height relative growth,ground diameter relative growth rate,aboveground biomass,underground biomass,total biomass;There was a significant positive correlation between soluble protein content and relative growth rate.4.With the decrease of pH value of simulated acid rain,relative conductivity,MDA content and SOD,POD and CAT activity of Alnoides seedlings were gradually increased,and the increase range was increasing,APX activity increased first and then decreased,PPO and GR activity showed an increase-decrease-increase trend.The content of MDA and relative conductivity of different simulated acid rain treatments were significantly higher than the control,and SOD,POD,CAT,APX,PPO and GR activity were higher than the control,but in simulated acid rain solution of pH 5.6 showed no significant difference with the control.The highest APX activity in simulated acid rain solution of pH 4.0,which was 354.84 U/(min g),significantly higher than the control and other treatment of simulated acid rain;PPO and GR activity respectively in simulated acid rain pH 2.0,pH 3.0 reached maximum,respectively 176.63,17.34 U/(min g),highly significant other than that of the control and treatment of simulated acid rain.Relative growth of seedling height and ground diameter volume relative growth,aboveground biomass,underground biomass,total biomass,root shoot ratio and cell membrane permeability,MDA content,SOD,POD,CAT,APX,PPO,GR antioxidant enzyme activity has significant negative correlation.In summary,mild simulated acid rain could promote the accumulation of biomass,chlorophyll content and free proline of Alnoides seedling,promote the growth of seedlings and the root shoot ratio increased;with the decrease of pH value of simulated acid rain and its active oxygen content of leaves increased,resulting in lipid peroxidation increased,the increase of MDA content,the soluble protein content of sugar soluble decreased and the degree of plant injury increased,increased the activity of antioxidant enzymes,which synergistic effect against the damage caused by acid rain. |
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