中文摘要：

以腾格里沙漠东南缘天然植被区藓类结皮和无结皮土壤为对象,采用野外原状土柱封顶埋管法对无机氮库和净氮转化速率的季节动态特征进行研究.结果表明：藓类结皮和无结皮土壤有效氮含量和净氮转化速率存在明显的季节变化特征,不同月份间差异显著.在非生长季,3和10月土壤有效氮含量和净氮转化速率显著高于其他月,氮矿化过程以固持态为主,两样地间土壤净氮转化速率无显著差异;在生长季,土壤有效氮含量和净氮转化速率显著增加,6—8月时达到峰值,分别为17.18 mg·kg-1和0.11 mg·kg-1·d-1.两样地土壤净硝化速率和净氮矿化速率在各月间差异显著,均表现为藓类结皮土壤〉无结皮土壤.土壤铵态氮和硝态氮含量4和5月时表现为藓类结皮土壤（2.66和3.16 mg·kg-1）〉无结皮土壤（1.02和2.37mg·kg-1）;6—9月则表现为无结皮土壤（7.01和7.40 mg·kg-1）〉藓类结皮土壤（6.39和6.36mg·kg-1）.藓类结皮的繁衍与拓殖能够调节土壤有效氮含量、促进土壤氮矿化过程,是影响土壤氮素循环的重要生物因素.

英文摘要：

Seasonal variations of soil inorganic nitrogen （N） pool and net N transformation rate in moss-covered soil and in the bare soil were comparatively observed by incubating intact soil columns with parafilm capping in the field in a natural vegetation area of Shapotou, southeastern fringe of the Tengger Desert. We found pronounced seasonal variations in soil available N content and net N transformation rate in both moss-covered soil and bare soil, with significant differences among differ- ent months. In non-growing season, soil available N content and net N transformation rate were sig- nificantly higher in March and October than in other months. Furthermore, immobilization was the dominant form of N mineralization, and no significant difference in net soil N mineralization rate was found between the two sampling soils. In growing season, soil available N content and net N trans- formation rate markedly increased and reached their peak values during June to August （ 17.18 mg · kg-1 and 0.11 mg ·kg-1 · d-1, respectively）. Both soil net nitrification and N mineralization rates in moss-covered soil were significantly higher than in bare soil. Soil ammonium and nitrate N content in April and May were higher in moss-covered soil （2.66 and 3.16 mg · kg-1, respectively） than in bare soil （ 1.02 and 2.37 mg · kg-1 , respectively） ; while the tendency was the converse in June and September, with 7.01 mg · kg-1 for soil ammonium content and 7.40 mg · kg-1 for nitrate N content in bare soil, and they were 6.39 and 6.36 mg · kg-1 in moss-covered soil, respectively. Therefore, the existence and succession of moss crusts could be considered as one of the important biological factors affecting soil N cycling through regulating soil available N content and promoting soil N mineralization process.