Effects Of Simulated Acid Rain On Growth And Physiology Of Four Tree Species Seedlings

Guangxi province is one of the most vulnerable areas of acid deposition and acid pollution. Acid rain can affect the normal metabolism of plants, resulting in a series of physiological and biochemical processes lose balance in plants. Therefore, to study on the mechanism of acid rain adaptation in these species in Guangxi district and the physiological changes of trees in acid condition, can provide reference for the research on the tolerance of the tree species, and provide a theoretical basis for the cultivation of important timber tree species and rare species in Guangxi. The paper studied the effects of acid rain in 4 different pH solutions (pH 3.0, pH 4.0, pH 5.0 and pH 5.6, pH 6.0 (contrast)) and treating E. grandis ×E.urophylla No.9, Erythrophleum fordii Oliv, Dalbergia odorifera T.Chen, Aquilaria sinensis (Lour.) Gilg which are planting in this area, the effects and the change regulation of acid rain on tree growth, cell membrane permeability and antioxidant enzyme system were studied. The result showed that:1. With the decrease of acid rain pH, relative growth yield and stems relative growth yield of the seedlings of the four species were all decreased. Under the simulated acid rain pH 3.0, the above ground biomass of E. grandis ×E.urophylla No.9 was significantly higher than that in the control; in pH 5.0, the below ground biomass and total biomass slightly greater than that in the control; in pH 5.6, the root shoot ratio was the highest. Under the simulated acid rain pH 5.6, the relative growth yield and root shoot ratio of Erythrophleum fordii Oliv were significantly higher than that in the control. Under the simulated acid rain pH 5.0, the relative growth yield of Dalbergia odorifera T.Chen were significantly higher than that in the control, and the root shoot ratio was the highest. In different concentrations of acid rain treatment, each growth index of Aquilaria sinensis (Lour.) Gilg were significantly lower than that in the control.2. With the decrease of acid rain pH, the chlorophyll a/b of four species in general showed that decreased first and then increased, the effect on the indexes of chlorophyll of different tree species of different acid rain pH was different, total chlorophyll content of four specie were significantly greater than the control at pH 3.0 and pH 4.0 and pH 5.0 and pH 5.6.3. With the decrease of acid rain pH, the cell membrane permeability and the content of MDA of the seedlings of the four species were all increased. The cell membrane permeability was positively correlated with the content of MDA in Erythrophleum fordii Oliv. Under the simulated acid rain pH 3.0, the cell membrane permeability and the content of MDA of four species was significantly higher than that in the control, and with the decrease of acid rain pH, the cell membrane permeability of E. grandis ×E.urophylla No.9 and Erythrophleum fordii Oliv were always increased, Dalbergia odorifera T.Chen showed the trend was increase-decrease-increase, and Aquilaria sinensis (Lour.) Gilg showed the trend was first increased and then decreased. From pH 5.6 to pH 4.0, the content of MDA in four species changes slowly; but from pH 4.0 to pH 3.0, was increased considerably. And at the same pH the cell membrane permeability of Aquilaria sinensis (Lour.) Gilg was higher than that in the other three species.4. With the decrease of acid rain pH, the activity of SOD, APX, CAT of E. grandis×E.urophylla No.9 were increased firstly and then decreased and the highest point were at pH 4.0, the activity of POD was always increased. The activity of SOD and APX in Erythrophleum fordii Oliv were increased firstly and then decreased, the highest point were at pH 4.0, the activity of POD and CAT were always increased. The activity of SOD, POD and CAT in Dalbergia odorifera T.Chen were decreased firstly and then increased, the activity of APX was increased firstly and then decreased, the highest point were at pH 4.0. The activity of APX and CAT of Aquilaria sinensis (Lour.) Gilg were increased firstly and then decreased, and the highest point were at pH 4.0, the activity of SOD and POD were always increased.5. The average membership degree of E. grandis xE.urophylla No.9 is maximum, is 0.760. The second is Dalbergia odorifera T.Chen, the average membership value of Aquilaria sinensis (Lour.) Gilg and Erythrophleum fordii Oliv are relatively small. The order of the four species against acid rain capacity was:Eucalyptus urophylla 9> Dalbergia odorifera> Aquilaria sinensis> Erythrophleum fordii.In summary, mild acid rain can also promote the accumulation of biomass and chlorophyll content in E. grandis ×E.urophylla No.9, and to promote the high growth and increased the root shoot ratio in Erythrophleum fordii Oliv and Dalbergia odorifera T.Chen. The effect of growth of Aquilaria sinensis (Lour.) Gilg was larger, and under mild acid rain can cause significant influence. At pH 4, the cell membrane permeability and the content MDA of the four tree species were significantly higher than the control, and the variety of antioxidant enzymes activity also reached the highest, which showed that the simulated acid rain had a serious damage to the cell membrane of the four tree species. Among them, the ability of E.grandis ×E.urophylla No.9 to resist acid rain stress is the strongest, the second is Dalbergia odorifera T.Chen, the ability of Aquilaria sinensis (Lour.) Gilg and Erythrophleum fordii Oliv to resist acid rain stress are relatively poor.