中文摘要：

在青藏高原三江源区草地上,以开顶式温棚模拟增温,在其内部施用不同形态氮素（硝态氮和氨态氮）比例的氮肥,对重齿风毛菊（Saussurea katochaete）的光合速率、叶绿素荧光及其群落总生物量进行研究,旨在为人工管理草场施肥提供指导。结果表明：重齿风毛菊的光合速率随硝态氮比例增加而下降,气孔导度则增加。其他气体交换参数没有规律性变化。光系统II（PSII）光化学量子产量（Φ_（PSII））在硝态氮比例为0%时最大,非光化学瘁灭（NPQ）则随硝态氮比例增大而增大。重齿风毛菊所在群落的总生物量在硝态氮和氨态氮比例平衡时达到最大。结果表明不同比例氮素施肥会对青藏高原草甸植物的净光合速率和群落总生物量产生影响。

英文摘要：

The Qinghai-Tibet Plateau is the region where is sensitive to the global warming.The climate changes affect all aspects of plants in the region and thus affect the productivity of alpine meadow.The open-top chambers were used to simulate the increasing temperature,and the fertilizers with different ratios of nitrate to ammonium were applied in the plots.The gas exchange and chlorophyll fluorescence of Saussurea katochaete Maxim and total biomass of the community were determined.The results showed that net photosynthetic rate of S.katochaete decreased as the ratios of nitrate to ammonium increased,but stomatal conductance increased.Other parameters of gas exchange showed irregular changes.Φ_（PSII）reached the peak when the ratio of nitrate to ammonium was 0%.Non-photosynthesis quenching increased as the ratios of nitrate to ammonium increased.In the community containing S.katochaete,the total biomass reached the peak when nitrate and ammonium was equal.All the results suggested that nitrogen fertilizers of different ratios of nitrate to ammonium might affect net photosynthetic rate of S.katochaete and the community biomass.Nitrogen fertilizer application is of significance to increase productivity of alpine meadow in Qinghai-Tibet Plateau.