中文摘要：

以腾格里沙漠东南缘的荒漠化草原为对象，设置添加0、1．75、3．5、7和14gN·m^-2·a^-15个氮素水平，研究了施氮对该地区土壤理化性质和土壤酶活性的影响．结果表明：施氮导致表层（0—10cm）和下层（10～20cm）土壤中总氮、NO3^--N、NH4＋-N和有效氮的累积，土壤pH下降，对土壤有一定的酸化作用．施氮明显抑制了土壤酶活性，且不同酶活性在氮素投加水平、土层深度和年际间有所差异．土壤酶活性与土壤氮素水平、土壤pH及土壤水分之间存在显著相关关系．

英文摘要：

To investigate the impacts of nitrogen （N） enrichment on soil physico-chemical property and soil enzyme activities in desert ecosystems, a field experiment by adding N at 0, 1.75, 3.5, 7, or 14 g N . m^-2 . a^-1 was conducted in a temperate desert steppe in the southeastern fringe of the Tengger Desert. The results showed that N addition led to accumulations of total N, NO3--N, NHa＋-N, and available N in the upper soil （0-10 em） and subsoil （10-20 cm）, however, reduc- tions in soil pH were observed, causing soil acidification to some extent. N addition pronouncedly inhibited soil enzyme activities, which were different among N addition levels, soil depths, and years, respectively. Soil enzyme activities were significantly correlated with the soil N level, soil pH, and soil moisture content, respectively.