放牧对小嵩草草甸生物量及不同植物类群生长率和补偿效应的影响

基于小嵩草(Kobresia parva)草甸连续2 a的牦牛放牧试验，研究了暖季和冷季放牧草场地上地下生物量及其分配规律、不同植物类群的绝对生长率生长率，探讨了放牧制度和放牧强度对不同植物类群补偿效应的影响。结果表明，随着放牧强度的增加地上总生物量呈减小趋势，放牧强度对暖季草场地上总生物量的影响极显著（P?0.01），对冷季草场地上总生物量的影响不显著（P?0.05）；两季放牧草场各土壤层地下生物量随放牧强度的增加呈明显下降趋势，放牧强度对暖季放牧各土壤层地下生物量的影响显著（P?0.05），对冷季放牧各土壤层地下生物量的影响不显著（P?0.05）；冷季放牧草场牧草生长季地下生物量与地上生物量的比值随放牧强度的增大而减小，暖季放牧草场对照区地下生物量与地上生物量的比值低于轻度放牧和中度放牧、高于重度放牧；暖季放牧草场各放牧处理不同植物类群均存在超补偿生长，但莎草科和禾本科植物的超补偿生长在8月份，阔叶植物的超补偿生长发生在6月和7月份，禾本科植物的超补偿生长效应强于莎草科植物和阔叶植物，轻度和中度放牧的补偿效应更明显；冷季放牧下不同植物类群也存在超补偿生长，但补偿效应不明现。因此,暖季适度（轻、中度）放牧利用更有利于产生超补偿生长,而重度利用对植被的稳定产生潜在的不利影响。

Influence of grazing on biomass, growth ratio and compensatory effect of different plant groups in Kobresia parva meadow

Alpine meadow is a major vegetation community on the Qinghai-Tibetan Plateau, China. Kobresia parva alpine meadow is regarded as one of the forage bases for yak production because of its high content of proteins, fats and carbohydrates. However, the alpine meadow vegetation degraded as overstocking. Therefore, it is important to study the effects of yak-grazing on Kobresia parva alpine meadow community. In this study, above- and below-ground biomass and their allocation, absolute growth ration, and influence of grazing intensity on compensatory effect of different plant groups were investigated, based on yaks grazing trial for 2 years in Kobresia parva meadow. Our results showed that total above-ground biomass followed a decreasing trend with the increase of grazing intensity. And, the total above-ground biomass showed a significant differences in the warm-season grazing pasture (P?0.01), but not in the cold-season grazing pasture (P?0.05) among grazing intensity. With the increased grazing intensity, the below-ground biomass for different soil depth appeared significantly decreasing trend in both the warm- and the cold-season grazing pastures, and there was significant difference for below-ground biomass of each soil depth in the warm-season grazing pasture (P?0.05), but not in the cold-season grazing pasture (P?0.05) among different grazing intensities. Moreover, the rate of below-ground biomass to above-ground biomass decreased along the increasing of grazing intensity in the cold-season grazing pasture, but, the rate of below-ground biomass to above-ground biomass in the control plot was less than that in the light and moderate grazing plots, and it was higher than that in the heavy grazing plot in the warm-season grazing pasture. Additionally, the over-compensatory growth was existed in the different plant groups for each grazing intensity in the warm-season grazing pasture. Meanwhile, the over-compensatory growth of Cyperaceae and Gramineae plant groups appeared in August, but it appeared in June and July for forbs plant group. Moreover, the compensatory effect of Gramineae plant groups was higher than that of Cyperaceae plant group and forbs plant group. The compensatory effects were more significant in the light and moderate grazing intensities. The over-compensatory growth also appeared for different plant groups in the cold-season grazing pasture, but the compensatory effect was non-significant. So, our results suggested that the modest grazing (the light and moderate grazing) would be beneficial to bring over-compensatory growth in the warm-season grazing pastures, and the heavy grazing would bring potentially disadvantage for vegetation stabilization in studied Kobresia parva meadow.