阿拉善高原荒漠植被组成分布特征及其环境解释 Ⅳ.土壤种子库特征研究

阿拉善荒漠土壤种子库种子密度主要受到水、热变化梯度的影响而呈现水平地带性分布规律。土壤种子库的分布主要集中在0～5cm的土层中,深层土壤很少有种子库的存在。阿拉善土壤种子库共统计到26种植物种子,分属9科22属,以禾本科最多;生活型以一年生草本植物种子的比例最高,达到51.36%。极端干旱环境条件下不存在有效的土壤种子库。土壤种子库多样性(Simpson指数)在东阿拉善草原化荒漠区为最高,在0.546～0.917之间;西阿拉善荒漠区次之为0.417～0.915;额济纳绿洲区为0.855,说明阿拉善荒漠区从东到西,土壤种子库物种多样性指数呈现下降的趋势。土壤种子库相似性研究表明,阿拉善荒漠不同区域的土壤种子库相似性差异较大,东阿拉善荒漠化草原植被区,相似性系数范围为0.17～0.67,西阿拉善典型荒漠区为0～0.75,额济纳戈壁荒漠区和东、西阿拉善土壤种子库的相似性系数范围是0～0.4。说明阿拉善荒漠区,由于生境和植被的异质性程度高,导致土壤种子库之间的差异性显著。阿拉善荒漠的土壤种子库和地上植被组成上差异显著,地上植被的优势种以旱生、中生灌木、半灌木为主,土壤种子库中以一年生、多年生草本为主,没有统计到灌木种子的存在,表明土壤种子库对于灌木层片更新和演替的贡献非常小。这些发现对了解干旱荒漠植被自然修复特点具有重要的潜在贡献。

Environmental Effects on Distribution and Composition of Desert Vegetations in Alxa Plateau:Ⅳ. Soil seed banks

Soil seed banks in Alxa desert present horizontal zonality mainly affected by water and heat gradients. Soil seed banks concentrate in the 0～5 cm soil layer, with very less seed banks exist in deeper soil layer. Twenty-six seeds in Alax desert have been checked and belong to 9 families and 22 genera, in which Gramineae was dominant family. Annual plant seeds make up 51.36% of all life forms. No effective seed banks appear under the extremely arid environment. Biodiversity of seed banks is the most(0.546～0.917) in steppe-desert of eastern Alxa, less in desert regions of western Alxa(0.417～0.915), and 0.855 in Ejin oasis, showing decreasing trend form east to west. Because of high heterogeneity of habitat and vegetation, the differences of seed banks similarity are obvious among regions in Alxa desert, ranging from 0.17～0.67 in steppe-desert of eastern Alxa, 0～0.75 in typical desert of western Alxa, and 0～0.4 in gobi desert of Ejin. Besides, the difference between species compositions of seed banks and aboveground vegetation is significant. The dominant species of aboveground vegetation are xerophytic and mesophytic shrubs or subshrubs, but that of seed banks are annual and perennial grasses without shrub seeds, which indicate that soil seed banks have little contribution to regeneration and succession of shrub layers.