高寒草地植物群落关键种对不同放牧家畜组合放牧的响应

如何通过合理的利用方式提高高寒草地管理水平，实现其可持续利用一直是草地生态学领域的研究热点。为明确不同放牧家畜组合下高寒草地植物群落关键种的演替规律及其驱动因素，基于中等放牧强度设置了不同放牧家畜组合放牧样地（牦牛单牧、藏羊单牧、牦牛藏羊1 ： 2混牧、牦牛藏羊1 ： 4混牧、牦牛藏羊1 ： 6混牧）以及围封样地，并在连续放牧处理7年后系统分析了不同放牧家畜组合下植物群落特征与土壤理化性质变化，以期确定最优放牧组合。结果表明：（1）不同放牧家畜组合均会显著降低高寒草地植物盖度，但对其物种丰富度与多样性指数的影响并不显著。（2）牦牛藏羊1 ： 2混牧下植物群落特征与禁牧处理下植物群落特征较为相似，且牦牛藏羊1 ： 2混牧下的植物群落稳定性最强、组织水平最高。（3）牦牛单牧与1 ： 2混牧下关键种为矮生嵩草；藏羊单牧下关键种为天山针茅；1 ： 4混牧下关键种为星毛委陵菜；1 ： 6混牧与围封下关键种为赖草。（4）围封能够显著降低土壤容重，藏羊单牧则会显著增加土壤容重与土壤速效氮、磷含量。（5）土壤速效氮、容重与含水量是驱动不同放牧家畜组合下植物群落关键种演替的重要理化因子。综上所述，中等放牧强度下，牦牛藏羊1 ： 2混牧是青藏高原高寒草地较为理想的利用方式。此外，相较于单纯增加草地物种丰富度或多样性，建立植物群落物种之间的有效关联是提高青藏高原高寒草地管理水平的另一关键途径。

Response of keystone species changes in alpine grassland plant communities to different herbivore assemblage grazing

How to improve alpine grassland management level and achieve its sustainable use through reasonable utilization has been a hot research topic in the field of grassland ecology. In order to clarify the succession patterns of keystone species of alpine grassland plant communities under different herbivore assemblage grazing and their driving factors, this study set up grazing plots (Yak grazing alone, Tibetan sheep grazing alone, Yak and Tibetan sheep 1:2 mixed grazing, Yak and Tibetan sheep 1:4 mixed grazing, Yak and Tibetan sheep 1:6 mixed grazing) and enclosure plots with different herbivore assemblages based on moderate grazing intensity, then systematically analyzed the changes of plant community characteristics and soil physicochemical properties under different herbivore assemblage after 8 years of continuous grazing treatment, hope to determine the optimal grazing combination. The results showed that:(1) Grazing significantly reduced plant coverage, but the effect of different herbivore assemblages on plant coverage and species richness was not significant. (2) The plant community characteristics during 1:2 mixed grazing were similar to those of plant communities with enclosure. At the same time, the plant community during 1:2 mixed grazing pocessed the highest community stability and organization level. (3) The keystone species showed obvious succession under different herbivore assemblages. The keystone species was Kobresia humilis under the treatments of yak only and yak:sheep as 1:2. The keystone species was Leymus secalinus under the treatments of enclosure and yak:sheep as 1:6. It was Stipa sareptana and Potentilla acaulis in sheep only and yak:sheep as 1:4, respectively. (4) Enclosure could significantly reduce soil bulk density, while Tibetan sheep grazing alone could significantly increase soil bulk density and soil available nitrogen and phosphorus content. (5) Soil available nitrogen, bulk density and water content were the key physical-chemical factors driving the changes of keystone species in plant communities under different herbivore assemblages. In summary, 1:2 mixed grazing of yak and Tibetan sheep under moderate grazing intensity is a best way to utilize alpine grasslands on the Tibetan Plateau. In addition, establishing effective associations between plant community species is another key way to improve the management level of alpine grasslands on the Tibetan Plateau compared to simply increasing the species richness or diversity of grasslands.