青藏高原东缘封育和退化高寒草甸种子库差异

摘要

采用幼苗萌发法研究了青藏高原东部高寒草甸封育和退化地区土壤种子库的差异.结果表明:(1)两个样地总共有10161株幼苗萌发,分属55个物种,23个科.封育样地多年生植物比例高于退化样地,禾草和单子叶植物比例在两个样地间差异不大.(2)退化样地土壤种子库种子密度((6105±1530) m-2)显著高于封育样地((3883±798) m-2),而物种丰富度差异不显著.所研究区域拥有较为丰富的种子库资源,退化地区资源更丰富,说明恢复不存在种子限制问题,土壤种子库可以成为植被恢复的潜在资源.(3)种子密度和物种丰富度在垂直分层上差异显著,且随着深度的增加而显著减小.(4)用Srensen coefficient指数计算出土壤种子库和地上植被之间的相似性在整体上较低,封育样地(45.3%)略高于退化样地(40.4%),两个样地地上植被之间的相似性为50%,而种子库之间相似性高达84.6%,说明种子库起到一个"缓冲器"的作用.(5)Shannon-Wiener多样性指数分析显示,无论在地上植被或种子库中,物种多样性都是封育样地显著高于退化样地.过度放牧不仅导致地上植被的生物多样性丧失,而且使种子库中的物种多样性降低,而封育管理可以维持地上植被和种子库中的物种多样性.%We used the direct germination method to examine the difference in the soil seed bank between an enclosed and a degraded alpine meadow in the eastern Tibetan Plateau. The main results and conclusions were: (1) A total of 10161 seedlings germinated in the two sites, belonging to 46 species and 23 families. The proportion of perennials was higher in the enclosed site than in the degraded site, but the proportion of grasses and monocotyledons was not different between the two sites. (2) The mean seed density in the degraded site ((6105±1530) viable seeds m-2) was significantly higher than in the enclosed site ((3883±798) m-2), but there was no difference in species richness between the two sites. The larger seed bank in the degraded area indicates that restoration of this habitat is not seed limited, and the soil seed bank has the potential to be a source for restoration. (3) Species richness and seed density decreased significantly with depth. (4) We used S rensen′s coefficient to evaluate the relationship between the presence of species in the germinable seed bank and the aboveground vegetation. This relationship was weak, though stronger for the enclosed site (45.3%) than for the degraded site (40.4%). However, the similarity of seed bank between the two sites was high (84.6%), indicating that while grazing pressure has a dramatic effect on vegetation, the impact of these changes is buffered by the soil seed bank. (5) The Shannon-Wiener index in the enclosed site was significantly greater than in the degraded site, both for the seed bank and for the aboveground vegetation. Thus, overgrazing reduces both the species diversity of aboveground vegetation and the diversity of the seed bank. Management by enclosing pastures could maintain the species diversity of both the seed bank and the aboveground vegetation.