【作者】 马妙君；

【导师】 杜国祯；

【作者基本信息】 兰州大学 ， 生态学， 2009， 博士

【摘要】 土壤种子库时期是植物种群生活史的潜种群阶段，反映了植被的演化进程，是植物群落的进化记忆。同时又是植被经历干扰后恢复的主要资源，在重塑和维持物种多样性以及退化生态系统的恢复与重建方面扮演着重要角色。目前，种子库的研究已成为植物生态学研究不可缺少的一部分。然而，对青藏高原高寒草甸种子库的研究处于空白状态，我们通过研究该地区种子库大小，物种组成，以及与地上植被间的关系，了解该地区土壤种子库分布格局，探讨种子库对地上植物群落构建中的作用，此外，本研究还可以对高寒草甸的管理，高寒地区退化生态系统的恢复与重建提供理论依据。我们得出以下主要结果：1)青藏高原东部高寒草甸拥有丰富的种子库资源，可萌发的种子库密度为674 seeds．m^-2-9779 seeds．m^-2。2)种子库种子密度随着干扰强度的增加而显著升高，而物种丰富度没有差异。种子密度和物种丰富度随着土壤深度的增加而减小。在种子库和地上植被中，多年生物种的比例随着干扰的增加而减小。在干扰地区大部分物种都具有持久性种子，说明这是对当前干扰的一种适应性对策。3) DCA结果显示，重度干扰地区的种子库与其地上植被物种组成相似性很高，说明种子库对地上植物群落构建中起到重要作用。此外，在重度干扰地区的种子密度高达6105 seeds．m^-2，其植被恢复不存在种子限制问题，所以种子库很有潜力成为地上植被恢复的资源。然而，在封育，对照，轻度干扰地区的种子库与其地上植被物种组成相似性低，说明种子库对地上植被的贡献较低，我们推测地上植物群落的更新很有可能依赖于种子扩散和克隆生长。4)随着演替年龄的增大，种子库种子密度显著降低（符合假说）；种子库物种丰富度和物种多样性显著增加（与假说相反）；种子库与地上植被之间的相似性逐渐降低。地上植被与土壤表层种子库的相似性最高，随着土壤深度的增加而逐渐减小。演替初期物种产出大量长寿命的种子，在土壤中保持活力超过20年。不同演替阶段种子库一直被演替初期的物种所占据，演替后期物种对种子库贡献较小。5) NMDS分析结果表明，地上植被的物种组成表现出明显的演替趋势，而种子库物种组成变化很小。在演替初期，种子库对地上植物群落构建起到很大的作用，随着演替的进程，种子库作用逐渐减小，随着多年生克隆物种的增加，我们推测，在演替的后期，地上植物群落的更新主要依靠克隆生长和种子扩散。6)随着海拔的升高，不论是在整体还是各个分层上，瞬时种子库还是持久种子库中，种子库种子密度和物种丰富度显著降低。多年生物种比例随着海拔的升高在地上植被中逐渐增加，而在种子库中差异不大。高海拔地区拥有更高的种子库种子消耗率。7)大部分物种在不同的海拔上都具有持久种子库。23．6％的物种的种子库对策随不同的环境而改变。我们的结果不支持假说“种子库对策是物种的固有特征”。8)基于在三个海拔水平上的结果，发现青藏高原东部高寒草甸持久种子库趋向于拥有更小的种子。种子大小和频度之间呈负相关关系，随着海拔的升高，负相关趋势有所增加，但不显著。说明种子库在更高海拔地区趋向于拥有更小的种子。种子大小和种子频度随着土壤深度的增加没有呈现出统一的规律。因此，我们认为种子大小的分布和土壤深度没有关系。9) Sorensen相似性分析结果显示，种子库与地上植被之间的相似性随着海拔的升高而降低。NMDS分析结果显示，在整体上，种子库与其地上植被的物种组成相似性低，随着海拔的增高，其相似性逐渐降低，说明在更高的海拔地区，种子库对其地上植被的贡献减小。更多还原

【Abstract】 The soil seed bank is one of the life history stages of plant populations, which iscalled subpopulation stage, and it is evolutionary memory of plant community whichreflects the evolution of the process of vegetation. Seed bank may function as a typeof genetic memory of a population, and play an important role in communitydynamics and regeneration. Seed bank is the major resource of vegetation restorationafter disturbance, and play a significant role in restoration and reconstruction ofdegraded ecosystem. At present, research of soil seed bank has become a recognizedand indispensable part of plant ecology now and has been an active research area. Sofar, no studies of seed banks from Oinghai-Tibet plateau exist. We through investigatethe size of seed bank, species composition, and relationship of seed bank andaboveground vegetation, attempting to find the distribution pattern of seed bank inthese areas, the role of seed bank in the process of plant communities construction.Moreover, this study provides a theoretical basis for restoration and reconstruction ofdegraded ecosystem in alpine areas.The result showed:1) There rich seed bank resources exist in the alpine meadow of easternQinghai-Tibet plateau. The mean viable seed density was 674 seeds.m^2- 9779seeds.m^-2.2) The density of buried seeds increased significantly with increasing disturbance,but no difference in species richness. Seed density and species richness decreasedwith depth. The proportion of perennial species decreased with decreasing disturbanceboth in seed bank and vegetation. A large portion of species with persistent seeds inthe disturbed areas indicate that it is a strategy of adaptation to current disturbance.3) Detrended Correspondence Analysis （DCA） showed significant differences ofspecies composition between seed bank and vegetation except the seriously disturbedsite. Our results suggest that the establishment of new species in severely disturbedareas is more dependent on the seed bank. The mean seed density was 6105 viableseeds.m^-2 in severely disturbed area, indicating that restoration of disturbed areas isnot seed limited, so the seed bank had a high potential for restoration of species-richvegetation. Oppositely, the restoration in less disturbed and mature meadows does notrely on seed banks, and the establishment of the vegetation in these communities is more likely to rely on seed dispersal and species with vegetative reproduction.4) The seed density in seed banks decreased with successional age, but speciesrichness and diversity increased. Hypotheses about changes in seed bank duringsuccession, predicting decreasing species richness and diversity, were not confirmed.The hypothesis that density of buried seeds declined during succession was confirmed.Similarity between the seed bank and vegetation decreased gradually with successionin the whole. The Vegetation is more similar to the seed bank in the shallow layer thanto the seed bank in the deeper soil, which shows that the vegetation contributes less tothe seed bank as soil depth increases, species of the later successional stagescontributed little to the seed bank. Most of species from early successional stageproduced longer-lived seeds, which stayed viable in the soil for a long period （morethan 20 years）. The seed bank was mainly composed of first successional speciesduring the whole successional range.5) The result of NMDS showed that during the course of succession, thevegetation showed a clear successional trend. However, this trend is not reflected inseed bank, and the species composition of seed bank is unvaried during thesuccessional process. We conclude that seed bank play an important role onvegetation in the early succession stage. In the later succession stages, the proportionof perennial was increase, seed bank’ role become weaker and weaker, so thecommunity regeneration is likely relies on vegetative reproduction and dispersal.6) The buried seed bank density and species richness decreased with the altitudeincrease whatever in the total or each separate soil layer, transient seed bank orpersistent seed bank. The proportion of perennial species increased with altitudeincrease in aboveground vegetation, but no difference in seed bank. The higheraltitude areas have higher seed bank depletion.7) The persistent seed bank was the most frequent strategy at all three altitudes.There 23.6% species in seed bank changed their strategy in different environment.The hypothesis "the seed bank strategy is a species’ inherent trait, i.e.," was notconfirmed in our study.8) Based on the results from three altitudes, we found the seed from persistentseed bank tend to have smaller seeds than species with transient seeds. Seed size wasnegatively correlated with seed frequency, and the tendency increased with altitudeincrease, but the correlation was not significant. This indicated that the smaller seedstend to exist in higher altitude area. The result showed there no relationship between seed size and seed frequency with soil depth increased, so we think there norelationship between seed size distribution and soil depth.9) The result of Sorensen indicated that the similarity of Seed bank andvegetation decreased with altitude increase. The result of NMDS showed that thespecies composition of seed bank and vegetation was low in the whole, and thesimilarity decreased with altitude increase, indicating that the contribution of seedbank to aboveground vegetation community was smaller in higher altitude areas.更多还原