酸性沉降与日本森林衰退

酸性沉降物包括干沉降物和湿沉降物，日本把pH值低于5.6的降水称为酸性降水。近年来，日本降雨的pH值为3.80～5.50。酸性沉降对森林生态系统的物质循环会产生一定的影响。人工模拟酸雨实验结果表明，pH值低于4时可减少杉木苗细根伸长和个体生长，而日本酸雨pH值多为4以上，可见酸雨直接造成杉木苗枯萎的可能性并不大，但酸雾的危害不可忽视；酸性沉降物与臭氧的协同作用越来越引起人们的关注。酸性沉降不仅对林木生长产生直接影响，而且通过土壤还对林木产生间接影响。对土壤酸化作为森林衰退可能原因之一也开展了深入研究，但目前有关森林衰退原因仍未得出一个肯定的结论。

Acid Deposit and Forest Decline in Japan

Acid deposits are fallen into two categories, the dry and wet. In Japan the precipitation with pH value less than 5.6 is called acid precipitation. In recent years, a lot of research has been carried out in the acid deposits related to forest decline in terms of the acid rain and matter cycling of forest ecosystem, the effects of acid deposit on forest tree growth and forest soil acidification. The experimental results of artificially simulated acid rain has shown that the elongation of fibrous roots of Cunninghamia lanceolata seedlings can be reduced if the pH value of acid rain is less than 4 even though the acid rain does not directly damage the seedlings. However,the effect of acid deposit associated with ozone is increasingly receiving more attention. The acid deposits have not only directly affected on tree growth but also indirectly through the acidification of forest soil which is probably one of the facts that cause forest decline.