Abstract: Grazing is the predominant use way of alpine meadows in the Qinghai-Tibet Plateau,with yaks and Tibetan sheep being the most common grazers. These livestock consume the aboveground portions of plants,leading to reduction in aboveground biomass and subsequently impact on plant community nitrogen pools. This study utilized grazing experimental sites within the Alpine-Grassland Livestock Adaptive Management Technology Platform to investigate the effects of different livestock types on nitrogen pools of alpine grassland communities. The results indicated that under no-grazing condition,alpine grassland aboveground biomass was 180.0 g·m^-2. Tibetan sheep grazing significantly decreased the aboveground biomass of plant communities. In ungrazed treatment,nitrogen content among functional groups was the following order:Legumes (26.4 mg·g^-1) > Forbs (17.0 mg·g^-1) > Grass (12.9 mg·g^-1) ≈ Sedge (11.8 mg·g^-1). Grazing significantly increased nitrogen content in grass and sedge,while had a smaller effect on forbs. The influence of grazing on nitrogen content of the community level was less pronounced than on individual functional groups,due to the inherent stability of plant communities. When subjected to grazing pressure,alpine grassland plant communities obtained more nitrogen from the soil to sustain growth,and grazing further exacerbated nitrogen limitation in these high-elevation ecosystems.

Key words: Grazing, Alpine grassland, Plant community, Functional group, Nitrogen pool

摘要： 放牧是青藏高原高寒草地最主要的利用方式，牦牛和藏羊是青藏高原最常见的放牧家畜，家畜通过采食植物地上部分会使地上生物量减少，进而对植物群落氮库产生影响。本研究依托青海省高寒草地-家畜系统适应性管理技术平台的放牧试验样地，探讨不同家畜类型放牧对高寒草地植物群落氮库的影响。研究结果表明：未放牧处理下高寒草地地上生物量为180.0 g·m^-2，藏羊单独放牧显著降低了植物群落地上生物量。对未放牧处理下不同功能群氮素含量的研究发现：豆科植物(26.4 mg·g^-1)>杂类草(17.0 mg·g^-1)>禾草(12.9 mg·g^-1)≈莎草(11.8 mg·g^-1)。放牧显著增加了禾草和莎草氮含量，对杂类草氮含量影响较小。放牧对群落水平植物地上部分氮含量的影响变化小于对各功能群的变化影响，因为植物群落具有稳定性。当高寒草地植物群落处于放牧压力下，会从土壤中获取更多的氮以维持生长，放牧会进一步加剧青藏高原高寒草地植物生长的氮限制。

关键词: 放牧, 高寒草地, 植物群落, 功能群, 氮库