中文摘要：

模拟研究了天然阔叶红松林和天然次生杨桦林不同氮沉降（0、25和50kgN·hm^-2·a^-1）水平下土壤酶活性（纤维素酶、多酚氧化酶和蔗糖酶）的变化趋势．结果表明：氮沉降增加对土壤酶活性的作用与林分类型有关，短期施氮可以显著影响土壤酶的活性；高氮沉降降低了土壤多酚氧化酶活性，且随着多酚氧化酶活性的降低，两种林型土壤纤维素酶和蔗糖酶活性也有降低的趋势．

英文摘要：

A simulation test was conducted to study the change trends of soil cellulase, polyphenol oxidase, and sucrase activities under natural broadleaf-Korean pine （Pinus koraiensis） and secondary poplar （ Populus davidiana） -birch （ Betula platyphylla） mixed forests as affected by 0, 25, and 50 kg · hm^-2 . a^-1 of N deposition. The results showed that the effects of elevated N deposition on test enzyme activities varied with forest type, and short-term nitrogen addition could significantly affect the test enzyme activities. High N deposition decreased soil polyphyneol oxidase activity, and correspondingly, soil cellulase and sucrase activities also had a trend of decrease.