Abstract: Fertilization is one of the main ways to improve grassland fertility in many grassland restoration measures. To explore the suitable amount of nitrogen (N) in alpine degraded grassland,four levels of nitrogen:N1 (10 kg·hm^-2),N2 (20 kg·hm^-2),N3 (30 kg·hm^-2),N4 (40 kg·hm^-2) were set as fertilization gradients. The effects of nitrogen application on the species diversity,productivity,and forage quality of the alpine degraded grassland community were studied. The results showed that with the prolongation of nitrogen application years,the number and diversity of species at different nitrogen application levels decreased significantly,but there was no significant difference among different nitrogen application levels. Nitrogen application increased the aboveground biomass of edible herbage,and the overall performance of N3 and N4 were higher than other levels. The aboveground biomass of each functional group had no significant difference among nitrogen application levels and the same nitrogen application level in different years. Nitrogen application significantly increased the crude protein and ether extract content of forage (P<0.05). With the increase of nitrogen application level,the contents of crude protein and ether extract showed an increasing trend,and the crude protein content of N4 level increased by 41.55%. Based on the principal component analysis and combined with the change characteristics of grassland communities,the nitrogen application rate of alpine degraded grassland was preliminarily set at 30 kg·hm^-2~40 kg·hm^-2. The results of this study can provide a theoretical basis for the sustainable restoration and management of alpine degraded grasslands.

Key words: Fertilization, Aboveground productivity, Species diversity, Forage quality

摘要： 施肥是众多草地恢复措施中提高草地肥力的主要方式之一，为了探讨高寒退化草地适宜的氮（N）添加量，以高寒退化草地为研究对象，设置不同施氮水平N1（10 kg·hm^-2），N2（20 kg·hm^-2），N3（30 kg·hm^-2），N4（40 kg·hm^-2），分析添加氮素对高寒退化草地群落物种多样性，生产力及牧草品质的影响。结果表明：随着施氮年份的延长，各施氮水平的物种数及多样性均明显降低，但各施氮水平间差异不明显；施氮增加了可食牧草地上生物量，总体表现为N3和N4水平高于其他水平，各功能群地上生物量在各施氮水平间以及同一施氮水平不同年份间的差异都不显著；施氮显著增加了牧草粗蛋白和粗脂肪含量（P<0.05），随着施氮水平的增加，粗蛋白和粗脂肪含量均呈增加趋势，其中N4水平粗蛋白含量提高了41.55%。通过主成分分析以及结合草地群落变化特征，将高寒退化草地施氮量初步定为30~40 kg·hm^-2。本研究结果可为高寒退化草地的可持续性恢复和管理提供一定的理论基础。

关键词: 施肥, 地上生产力, 物种多样性, 牧草品质