Abstract: In order to explore the suitable amount of nitrogen(N) and phosphorus (P) in the light degraded alpine grassland in the surrounding area of Qinghai lake,screen the optimized combination of N and P,urea and diammonium phosphate were used for this study and conducted with a randomized block design. Three levels of N (35,70,140 kg·hm^-2) and three levels of P (26,52,65 kg·hm^-2) were set with the combinations of N and P levels:N1P1 (35,26 kg·hm^-2),N1P2 (35,52 kg·hm^-2),N1P3 (35,65 kg·hm^-2),N2P1 (70,26 kg·hm^-2),N2P2 (70,52 kg·hm^-2),N2P3 (70,65 kg·hm^-2),N3P1 (140,26 kg·hm^-2),N3P2 (140,52 kg·hm^-2),N3P3 (140,65 kg·hm^-2) as 9 fertilization gradients,with no fertilization as a control. The effects of N and P combined application on the community characteristics of grassland community were studied for the year and the following year of fertilization. The results showed that,the combined application of N and P significantly (P<0.05) increased the coverage,height and important values of Gramineae and Leguminosae. The diversity of plant communities in alpine grassland were reduced,but not significant(P>0.05). The aboveground biomass of plant communities increased by 59.22%~205.67% and 73.41%~180.10% in the year and the following year of fertilization;Compared with the current year,the aboveground biomass increased by 2.72%~17.34% in the following year. The optimal N and P additions for plant growth in this area were 70~140 kg·hm^-2 and 26~52 kg·hm^-2. In summary,artificial fertilization is a rapid and effective measure for the improvement of light degraded grassland in natural alpine grassland,which can effectively improve grassland biomass and facilitate grassland vegetation restoration.

Key words: Nitrogen, Phosphorus, Alpine steppe, Diversity, Biomass

摘要： 为探讨环青海湖区域轻度退化高寒草原适宜的氮（N）、磷（P）添加量，筛选区域N，P合施的优化方案，本试验选用尿素与磷酸二铵，采用随机区组设计，设置3个氮元素水平（35，70，140 kg·hm^-2）和3个磷元素水平（26，52，65 kg·hm^-2），氮元素和磷元素水平组合为：N1P1（35，26 kg·hm^-2），N1P2（35，52 kg·hm^-2），N1P3（35，65 kg·hm^-2），N2P1（70，26 kg·hm^-2），N2P2（70，52 kg·hm^-2），N2P3（70，65 kg·hm^-2），N3P1（140，26 kg·hm^-2），N3P2（140，52 kg·hm^-2），N3P3（140，65 kg·hm^-2）9个施肥梯度，以不施肥为对照，研究N、P合施当年和次年对该草原群落特征的影响。结果表明：N、P合施显著（P<0.05）增加禾本科、豆科植物的盖度、高度和重要值。施肥不同程度降低了高寒草原植物群落多样性，但差异性不显著（P>0.05）。施肥当年与次年地上生物量分别增产59.22%~205.57%，73.41%~180.10%，次年比当年增产2.72%~17.34%。该区域最适宜植物生长的N、P添加量分别为70~140 kg·hm^-2，26~52 kg·hm^-2。综上所述，人工施肥是天然高寒草原轻度退化草地改良一种快速有效的措施，能够有效的提高草地生物量，同时也有利于草地植被的恢复。

关键词: 氮, 磷, 高寒草原, 多样性, 生物量