Abstract: In this paper,we investigated species composition,seed density,distribution characteristics,influencing factors of soil seed bank in subalpine grassland of Loess Plateau. There are 31 species of aboveground plants in research area,belong to 14 families and 25 genera,and there are 32 species of soil seed bank plants,which belong to 14 families and 31 genera. 83.45% of the soil seed bank in subalpine grassland was distributed in shallow layer soil (0~5 cm). With the aggravation of grassland degradation,the proportion of perennial plants in aboveground and underground seed banks decreased,and the density and richness of soil seed banks decreased significantly (P<0.001). There were more annual plants above ground in extremely degraded plots,which were consistent with that in underground seed banks. The species composition between aboveground vegetation and underground seed bank in plots with mild and moderate disturbance weas significantly different (P<0.01). In conclusion,the degradation of subalpine grassland has a great impact on the soil seed bank,and soil pH and soil moisture are the main environmental factors affecting seed bank density and richness. Because of the low density of the soil seed bank,artificial assistance is needed to restore vegetation in extremely degraded grassland rather than natural renewal.

Key words: Soil seed bank, Subalpine grassland, Land degradation, Diversity

摘要： 本试验对黄土高原亚高山草地不同退化程度下土壤种子库的物种组成、种子密度、分布特征以及影响因素进行了研究。结果表明，研究区地上植物有31种，分属于14科、25属；种子库植物有32种，分属于14科、31属；种子库的83.45%都分布于浅层土壤中（0~5 cm）。随着草地退化程度的加重，地上植被和地下种子库中多年生植物的比例减少，种子库密度与丰富度都显著下降（P<0.001）；极度退化样地的地上一年生植物增多，物种组成与地下种子库相似；轻度和中度干扰的样地中，地上植物与种子库的物种的组成具有显著差异（P<0.01）。总之，亚高山草地退化对土壤种子库产生了较大的影响，其中土壤pH与水分是影响种子库密度与丰富度主要的环境因素。极度退化草地种子库密度极低，地上植被靠自然更新很难恢复，需人工辅助。

关键词: 土壤种子库, 亚高山草地, 土地退化, 多样性