Abstract: Soil microorganisms are important regulators of soil nutrient release and retention. The differences in soil physicochemical properties and soil microorganisms under four grazing intensities of sheep grazing (control blank CK:0,light grazing LG:2 sheep·hm^-2,moderate grazing MG:4 sheep·hm^-2,heavy grazing HG:6 sheep·hm^-2) were investigated,and the effects of different grazing intensities on soil microbial nutrient metabolism were analyzed. The results showed that:in general,the soil carbon (C),nitrogen (N) and phosphorus (P) contents decreased under grazing interference,while the microbial C,N and P contents and their stoichiometry changed a little. The activity and stoichiometry of C-acquiring enzyme (β-glucosidase) in heavy grazing treatment were significantly higher than those in other treatments. In addition,the C:P imbalance and N:P imbalance in the moderate and heavy grazing were higher than those of CK,while the C:N imbalance was lower than that of CK,indicating that moderate or heavy grazing can lead to alpine grassland be relatively limited by carbon and phosphorus. The soil microorganisms mainly balanced the nutrients mismatch between themselves and resources by increasing the C-acquiring enzyme secretion under heavy grazing in alpine grassland.

Key words: Grazing intensity, Soil nutrient, Soil microbial biomass, Soil enzyme activity, Ecological stoichiometry

摘要： 土壤微生物是土壤养分释放或固持的重要调节者。本实验以青藏高原高寒草原为研究对象，以藏羊放牧强度控制实验为平台(对照(CK，0)，轻度放牧(LG，2 sheep·hm^-2)，中度放牧(MG，4 sheep·hm^-2)，重度放牧(HG，6 sheep·hm^-2))，开展不同放牧强度下高寒草地土壤和微生物养分变化特征及其对土壤微生物养分代谢的影响研究。结果显示：总体上，土壤碳氮磷含量在放牧干扰下呈减少趋势，而微生物碳氮磷含量及其化学计量的变化幅度较小；重牧的碳获取酶(β-葡萄糖苷酶)活性及化学计量显著高于其余处理。此外，中牧和重牧的C∶P不平衡和N∶P不平衡高于CK，而C∶N不平衡低于CK，这表示在中度或重度放牧下高寒草地主要受到碳、磷的限制。当面对自身与资源之间的养分不匹配时，高寒草地土壤微生物主要通过增加碳获取酶的分泌，来缓解在重牧下的养分限制。

关键词: 放牧强度, 土壤养分, 土壤微生物生物量, 土壤酶活性, 生态化学计量学