摘要

放牧对草地生态系统的影响是全球畜牧生态学研究的焦点。过度放牧导致草地退化严重，虽然在青藏高原地区已有较多放牧对草地影响的研究，但探究连续四年放牧对高寒草地生态系统影响的定位实验却鲜见报道。本研究在青藏高原东缘选取典型高寒草地，设置了4个牦牛放牧强度(禁牧：无放牧、轻牧：1头/hm2、中牧：2头/hm2和重牧：3头/hm2)以研究其对高寒草地土壤和植物功能的影响。开展四年试验后的结果表明：

放牧处理增加了植物种类，除部分科属重要值随放牧强度的增加而增大外，其余科属均减小；植物α多样性方面，物种丰富度的中牧处理显著高于禁牧处理；Simpson指数Shannon-Wiener指数和Pielou指数放牧处理均显著高于禁牧处理；放牧可以显著降低植物地上生物量。

放牧条件下土壤含水率显著增加；而土壤容重、全磷和有机碳含量对放牧强度均无显著性响应；土壤全氮和pH的响应主要在表层0-20cm，其中全氮为轻牧和重牧处理分别显著高于中牧，中牧处理下的土壤pH为显著高于轻牧；土壤全钾含量在禁牧处理中显著高于放牧处理；而土壤有效氮和速效钾均为中牧处理显著高于禁牧；土壤C:N主要表现在0-10cm土层，其中，中牧处理显著高于禁牧处理，而土壤C:P、C:K和N:P的响应主要在10-20cm土层，均表现为重牧处理显著高于禁牧处理。

综上所述，牦牛放牧强度显著影响土壤含水率、有效养分、植物多样性和植物地上生物量，而对其它土壤理化性质影响较弱。本研究结果为揭示放牧对高寒草地生态系统的影响提供了基础数据。

关键词：青藏高原；放牧强度；植物群落特征；土壤理化性质；

Abstract

Grazing effects on grassland ecosystem is one of the major issues of animal ecology.Overgrazing has caused serious grassland degradation.While there are many studies that addressed the effects of grazing on grassland ecosystems,little information on the effects of yak grazing intensity is revealed.In this study,four yak grazing intensities(no grazing,light grazing:1 yak/ha,moderate grazing:2 yaks/ha,and heavy grazing:3 yaks/ha)were set up in a typical alpine grassland on the eastern Qinghai-Tibet Plateau to test their effects on soil properties and plant growth.After four-years experiment,we found that:

Grazing treatments increased plant species,and the importance values of some families and genera increased with the increase of grazing intensity,but all the other families and genera decreased.In terms of plantαdiversity,the species richness under moderate grazing was significantly higher than no-grazing.Simpson index Shannon-Wiener index and Pielou index were significantly higher under grazing treatments than no grazing.Grazing also significantly reduced aboveground biomass of plants.

soil water content increased significantly under grazing treatments.Soil bulk density,total P and organic carbon showed no significant responses.Soil total N content was significantly higher under light and heavy grazing than that under moderate grazing.Conversely,soil pH was significantly higher under moderate grazing than light grazing.Soil total K content under no grazing was significantly higher than that under grazing treatments.Soil available N and K contents were only significantly higher under moderate grazing than no grazing.Conversely,soil C:N was significantly higher under moderate grazing than no grazing.The soil C:P,C:K and N:P were significantly higher under heavy grazing than no grazing.

In short,yak grazing intensities significantly altered soil water content,available N,K,plant diversities and plant aboveground biomass,but had weak effects on other physiochemical properties.Our results provide basic data for understanding the effects of grazing on grassland ecosystem on the Qinghai-Tibet Plateau.

Key words: Qinghai-Tibet Plateau；Grazing intensity；Soil physiochemical properties；Plant community characters.