中文摘要：

本文以黄土高原丘陵区陕北延安燕沟流域为例，研究了退耕地土壤有机碳、全氮和酶活性对植被恢复过程的响应。结果表明，随植被恢复年限的增加，植被盖度、多度和物种数均呈现先增加后减少然后又增加的趋势。同当年对照农地相比，随着植被恢复年限的增加，表层（0～20cm）土壤有机碳、全氮、蔗糖酶、脲酶和碱性磷酸酶活性均明显增加，过氧化氢酶活性随植被恢复年限的增加变化不明显。同对照农地相比，表层土壤有机碳、全氮、蔗糖酶、脲酶和碱性磷酸酶活性分别增加了35％～184．6％、5．7％～157．4％、89．6％～566％、32．9％～331．2％和0．18％～184．8％。表层土壤有机碳和脲酶活性对植被恢复的响应是在植被恢复初期（0～8年），随植被恢复年限的增加而增加，植被恢复8～29年期间，随植被恢复年限的增加而减少，而植被恢复29a以后，又随植被恢复年限的增加而增加。而表层土壤全氮、蔗糖酶和碱性磷酸酶活性对植被恢复的响应是在植被恢复初期（0～16年），随植被恢复年限的增加而增加，植被恢复16～29年期间，随植被恢复年限的增加而减少，植被恢复29a以后，又随植被恢复年限的增加而增加。表层土壤蔗糖酶、脲酶和碱性磷酸酶活性与有机碳和全氮呈极显著的相关关系，而表层土壤过氧化氢酶活性与有机碳和全氮相关性不明显。

英文摘要：

Taking the Yangou watershed located at hilly-gully region of the Loess Plateau as an example, the responses of soil organic carbon, total nitrogen and enzymatic activity on abandoned lands to vegetation restoration were studied. The results showed that with an increase of vegetation restoration years, change tendency of vegetation coverage, vegetation abundance, and amount of species was increasing in the beginning of vegetagion restoration （4-16 years）, then decreasing （16-29 years or 16-55 years）, and later increasing again （after 29 years or 55 years）. Compared to cropland, topsoil （0-20 cm） organic carbon, total nitrogen, invertase activity, urease activity, and alkaline phosphatase activity significantly increased with an increase of vegetation restoration years, but change of soil catalase activity with an increase of vegetation restoration years was not obvious. Compared to the cropland, topsoil organic carbon, total nitrogen, invertase activity, urease activity, and alkaline phosphatase activity increased by 35 % - 184.6 %, 5.7 % - 157.4 %, 89.6 % - 566 %, 32.9 % -331.2 %, and 0.18 96-184.8 %, respectively. The responses of topsoil organic carbon and urease activity to vegetation restoration were that in the beginning of vegetation restoration （0-8 years）, both of them increased with an increase of vegetation restoration years; during 8-29 years of vegetation restoration, both of them decreased with an increase of vegetation restoration years; after 29 years of vegetation restoration, both of them increased again with an increase of vegetation restoration years. The responses of topsoil total nitrogen, invertase activity, and alkaline phosphatase activity to vegetation restoration were that in the beginning stage of vegetation restoration （0-16 years）, three of them increased with an increase of vegetation restoration years; during 16-29 years of vegetation restoration, three of them decreased with an increase of vegetation restoration years, and after 29 years of vegetation resto