Effects Of Simulated Acid Rain On Ecophysiological Characteristics Of Quercus Mongolica And Quercus Variabilis Seedlings

With the acceleration of the process of global industrialization, impacts of acid precipitation, which were caused by atmospheric pollution, on the ecological environment are worsening. Acid rain has become a serious environmental problem globally and got more and more attention. Acid rain is the general term of atmospheric precipitation pH of less than5.6in all its forms, including rain, snow and hail. Acid rain was defined scientifically as acid deposition, including wet and dry deposition. Firstly, acid rain affects terrestrial ecosystems and enters the soil to affect the physical and chemical properties of soil. In terrestrial ecosystems, plants are the main receptors of to acid rain pollution. Therefore, studies of the effects of acid rain on plants are an ecological hotspot. Acid rain affects plants directly by leaching the canopy of forests and leaves. On the other hand, acid rain can cause soil acidification and base cations leaching, which can affect plants indirectly. In the past two decades, acid rain in China expanded continuously to north and the acidity significantly enhanced gradually. In some areas, such as Beijing, Shanxi, Henan and Shandong provinces, the frequency of acid rain, even serious acid rain, achieved the highest value in2008since1993. Monitoring data by years have shown that acid rain pollution in northern China has gotten significantly worse. Thus, studies on growth and physiological characteristics of typical species to acid rain in northern China have important values for understanding the effects of acid rain on forest community and vegetation restoration. Therefore, we chose the one-year-old seedlings of Quercus mongolica and Quercus variabilis to study the effects of simulated acid rain. The two kinds of seedlings were exposed to12simulated acid rain treatments of4different acidity gradients (severe, moderate, slight and control) by3rainfall levels (natural rainfall in summer and increase or decrease by30%). Simulated acid rain was applied to seedlings weekly. Growth, biomass, physiological characteristics and their potting soil were measured in seedlings of Q. mongolica and Q. variabilis. The effects of different pH value and rainfall of simulated acid rain on ecophysiological characteristics were analyzed and discussed.The results showed that potting soil, growth, biomass and physiological characteristics were significantly influenced by simulated acid rain in Q. mongolica and Q. variabilis. But the impacts were different in these two seedlings. By inputting the H+, simulated acid rain reduced the pH of potting soil under both two species. Effects of acid rain on other properties, such as, organic matter, total nitrogen, available P and available K were different etween species. Potting soil under Q. mongolica got more influences. Content of organic matter, total nitrogen and available P were significantly affected, while only available K were affected by simulated acid rain in potting soil under Q. variabilis. Biomass of these two species was reduced by low rainfall significantly, while the allocation to root was increased. With the decline in rainfall, height of seedlings decreased. However, the increase in acidity of acid rain promoted the growth and biomass. So in the perspective of growth, Q. mongolica got some resistance and adaptability to acid rain.Simulated acid rain can affect several physiological characteristics of Q. mongolica and Q. variabilis in different parameters. The high acidity of acid rain damaged the water-retention capacity of leaves and normal physiological activities of roots by increasing the water loss rate and decreasing the root activity of these two species. It also damaged the PS Ⅱ reaction center by hindering the transfer of photoeiectrons of Q. variabilis. Nevertheless, the decline of rainfall increased the chlorophyll content of Q. variabilis and NPQ of Q. mongolica.In conclusion, as the main tree species of deciduous broad-leaved forest in northern China, Q. mongolica and Q. variabilis had varying degrees of buffer capacity and adaptability. By comparising the effects of simulated acid rain on these two species, we found Q. mongolica is the more resistant species to acid rain. Therefore, in the situation of serious acid rain in northern China, we can choose Q. mongolica, which is a kind of typical broad-leaved species and also has resistant to acid rain, as the pioneer and constructive plants for the recovery of acid regions. The results have important implications for recovery of ecosystem’s structure and function in regional environmental stress.