what is the effect of acid rain on the growth of seedlings??

The effect of acid deposition on a particular ecosystem depends largely on its acid sensitivity, its acid neutralization capability, the concentration and composition of acid reaction products, and the amount of acid added to the system. As an example, the major factors influencing the impact of acidic deposition on lakes and streams are
(1) the amount of acid deposited;
(2) the pathway and travel time from the point of deposition to the lake or stream;
(3) the buffering characteristics of the soil through which the acidic solution moves;
(4) the nature and amount of acid reaction products in soil drainage and from sediments; and
(5) the buffering capacity of the lake or stream.
Acid precipitation may injure trees directly or indirectly through the soil. Foliar effects have been studied extensively, and it is generally accepted that visible damage occurs only after prolonged exposure to precipitation of pH 3 or less (for example, acid fog or clouds). Measurable effects on forest ecosystems will then more likely result indirectly through soil processes than directly through exposure of the forest canopy. Many important declines in the condition of forest trees have been reported in Europe and North America during the period of increasing precipitation acidity. These cases include injury to white pine in the eastern United States, red spruce in the Appalachian Mountains of eastern North America, and many economically important species in central Europe. Since forest trees are continuously stressed by competition for light, water, and nutrients; by disease organisms; by extremes in climate; and by atmospheric pollutants, establishing acid deposition as the cause of these declines is made more difficult. Each of these sources of stress, singly or in combination, produces similar injury. However, a large body of information indicates that accelerated soil acidification resulting from acid deposition is an important predisposing stress that in combination with other stresses has resulted in increased decline and mortality of sensitive tree species and widespread reduction in tree growth.
Soil biology can be seriously damaged by acid rain. Some tropical microbes can quickly consume acids but other microbes are unable to tolerate low pHs and are killed. The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins and leach away essential nutrients and minerals.
Acid rain can slow the growth of forests, cause leaves and needles to turn brown and fall off and die. In extreme cases trees or whole areas of forest can die. The death of trees is not usually a direct result of acid rain, often it weakens trees and makes them more susceptible to other threats. Damage to soils (see above) can also cause problems. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.
Other plants can also be damaged by acid rain but the effect on food crops is minimized by the application of fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands. Acid Rain depletes minerals from the soil and then it stunts the growth of the plant.
I hope this can help with your understanding. =)

你不是 twins，何來＜十億＞？

acid rain = acid + rain
acid will eat the plant and water help spread of acid