密度对濒危物种疏花水柏枝幼苗存活与生长的影响

疏花水柏枝(Myricarialaxiflora)原产于三峡库区长江干流的河滩,三峡水库的蓄水淹没了其所有的野生种群,使之濒临绝灭。通过一系列的密度处理实验,我们研究了不同密度下疏花水柏枝幼苗的存活率、幼苗总生物量、地下生物量、地上生物量、一级枝数、二级枝数、一级枝长度的变化,揭示了密度对一年生幼苗存活与生长的影响。结果显示,随着密度的增加,疏花水柏枝种群内部的竞争加剧,幼苗的死亡率增加,特别是当密度大于250ind./m2时,死亡率显著上升,上述体现植株生长状况的各指标值也随密度的增加而显著减小。表明疏花水柏枝一年生幼苗的存活与生长受到密度的影响。文中还建立了密度影响下疏花水柏枝各构件部分生长发育的回归模型,解释了密度对它们的调节作用。最后对疏花水柏枝种群重建中的相关问题进行了分析讨论,以求为回归引种实践提供参考。     

三峡库区特有植物疏花水柏枝的调查研究

疏花水柏枝是三峡大坝建成后唯一１种痊全部被淹没的库区特有植物物种。在实地系统调查的基础上,阐述了疏花水柏枝的形态特征,分布现状,生长环境和群落结构等特点;从生物学,生态学角度分析了它在长江沿岸消涨带内汛期被洪水淹没的生长特性。     

大型水库消落带中西来稗种子耐淹性沿高程梯度的种内分化

大型水库消落带中西来稗种子耐淹性沿高程梯度的种内分化 在水文节律稳定、每年蓄水时间很长且水位涨落落差很大的水库中,生长在水库库岸消落带不同高程区域中的植物每年要面对长时间的不同强度的水淹,这种每年发生持续的水淹胁迫可能会导致水库库岸消落带中生长的植物的种子耐淹能力发生种内分化。西来稗(Echinochloa crusgalli var. zelayensis)是在三峡水库消落带中自然生长的优势一年生植物,在三峡水库消落带植被及消落带生态环境保护中发挥着重要作用。本研究的目的在于探究三峡水库消落带中生长的西来稗种子的耐淹能力是否已发生种内分化,以及此分化的发生是否与较弱的种子扩散能力有关。在本研究中,采集来自三峡水库消落带不同高程区域中生长的西来稗种子,在三峡水库即将蓄水时将所有采集的种子放置于三峡水库消落带中4个不同高程位置接受不同深度不同时长的水库蓄水水淹,同时把所有采集的种子也放置于不会被水库蓄水淹没的非消落带河岸上作为对照处理;测定种子在水中的漂浮持续时间和蓄水期间水库水位上涨速度以量化在水库蓄水水位上涨时种子的扩散能力,水库蓄水结束水退后检测放置于水库消落带和非消落带河岸上的种子的种子完好率、种子萌发能力和成苗率。研究结果发现,在经历三峡水库蓄水水淹后,西来稗种子的完好率和最终成苗率随种子母株在消落带中所处的高程的增加而显著降低,表明在三峡水库成库运行七年后,在三峡水库消落带中生长的西来稗的种子耐淹能力已发生了种内分化。三峡水库蓄水水位上涨时西来稗种子在水中较短的漂浮持续时间和水库蓄水时较慢的水位上升速度限制了西来稗种子的水媒传播和扩散距离,从而有利于西来稗种子的耐淹能力发生种内分化。     

三峡库区消涨带特有植物疏花水柏枝(Myricaria laxiflora)的自然分布及迁地保护研究

疏花水柏枝为三峡库区消涨带特有植物,三峡工程的兴建将导致其野生居群全部灭绝。作者对该植物的地理分布、自然生境和群落结构进行了系统调查,发现疏花水柏枝分布于三峡库区重庆市巴南区至湖北省宜昌县间12个县级单位的长江干流消涨带,共31个居群9万余株,比原已知的分布区增加了7个县级区域18个居群8万余株。调查中发现该物种具有喜温湿、耐水淹和生长反季的生长习性,具有种子多、易扦插的繁殖优势和自然居群中物种少、水淹前后物种组成有差异的群落结构特点。同时,较系统地回顾了目前关于疏花水柏枝迁地保护的研究进展,探讨了其特殊的生态适应策略、起源进化和传播的可能途径以及濒危机制,并对下一步的保育研究提出了建议。     

三峡库区多年高水位运行对消落带狗牙根生长恢复的影响

为深入了解三峡库区多年高水位运行对消落带优势植物生长恢复的影响,分别于2008年和2017年定量调研了库区长寿段消落带狗牙根(Cynodon dactylon)种群的变化,探讨了库区高水位运行对消落带狗牙根萌发、生长和物质分配的影响。结果表明,多年的高水位运行导致不定芽形成和萌发显著被促进,形成更多的分株;高水位运行导致狗牙根分株的株高、茎宽和叶片数被显著抑制,而叶长和种群的总叶片数被显著促进,且随着消落带水位的降低叶长呈降低趋势,而叶宽和总叶片数呈增加趋势;高水位运行导致狗牙根种群匍匐茎和地下茎的茎长、茎节数和总茎长均被显著促进,且随着消落带水位降低匍匐茎茎长和茎节数呈显著的降低趋势,而地下茎茎长和茎节数呈增加趋势;高水位运行导致狗牙根地下茎储存的干质量呈增加趋势,而分株和匍匐茎的干质量呈降低趋势,而且在种群物质分配中地下茎所占的比例呈增大趋势,低水位狗牙根种群的分株和高水位种群的匍匐茎所占的比例也呈增加趋势。因此,狗牙根不仅具有很强的耐淹和生长恢复能力,也具有很强的拓殖能力,可以作为库区中低位消落带恢复和重建的主要原生物种。     

三峡大坝下游残存疏花水柏枝种群结构和动态

在三峡大坝下游的湖北宜都关洲设立1个40 m×40 m的固定样地,利用高度分级,比较2008与2009年两年间的疏花水柏枝（Myricaria laxiflora）种群数量动态,并运用点格局的Ripley＇s K函数分析了其空间格局变化及种群更新特征。结果表明,疏花水柏枝幼苗数量较少,种群更新存在一些障碍。空间分布格局与空间尺度及植株的大小密切相关。种群总体呈集群分布,各大小级多在9 m时出现最大的聚集强度,随着大小级的增加,聚集强度有减弱的趋势。幼苗与中株有较强的正关联。由于种群现有生境变化较大,应考虑迁地保护,并对原生种群加强长期动态监测;同时,开展疏花水柏枝适应机理研究,实施科学保护。     

三峡库区两种特有植物天然生境与迁地生境土壤特征的比较

对库区特有的濒危植物荷叶铁线蕨、疏花水柏枝天然生境和迁地保护区生境及其土壤性质进行了调查分析和比较,结果表明：荷叶铁线蕨适宜于温暖湿润且排水良好的条件下发育的酸性淋溶土,养分含量高,多为粘土。疏花水柏枝适宜于亚热气候下弱碱性、养分含量低的冲积性砂砾质初育土、能耐一定程度的盐分。中国科学院武汉植物研究所内的迁地保护区土壤为湖滨沉积物上发育的中性粘土、主要养分和盐分含量介于两种天然生境土壤之间。微量元     

三峡水库消落带植被高程梯度分异及其对生境胁迫的响应

三峡水库蓄水运行形成的极端生境胁迫深刻改变了消落带植被结构和功能。在消落带横向断面高程梯度上,植被生境具有典型的空间异质性。选取三峡水库典型自然恢复消落带,通过野外调查和室内分析,揭示了消落带自然演替植被的群落构成、物种多样性和生物量随高程梯度的分异特征,系统分析了极端淹水、侵蚀-沉积、土壤环境等生境胁迫类型对消落带植被高程梯度分异的影响。结果表明：①研究消落带适生植被以草本为主,共有15科25种23属,其中禾本科种类较多,但单属单种、单优群落现象明显;一年生和多年生草本分别占52%和48%,且一年生草本多在消落带上部定居,多年生草本主要在消落带下部聚集。②物种多样性指数与高程呈正相关趋势,在145-150m范围内较低,在160-170m范围内较高。③植被生物量为199.68-1211.2g/m²,总体呈现随高程增加而显著增加的趋势;受多种生境因子的复合胁迫影响,生物量随高程存在局部波动。④水库水位变动形成淹水时长、出露时令、淹水强度等是影响消落带植被生物量高程梯度分异的主导因子;侵蚀/沉积过程改变土层厚度、根层土壤持水能力和肥力条件,对植被生长产生重要影响;土壤水分和氮是植被生长的限制性因子。因此,优势生境适宜性物种选育、土壤基质保育和植被格局功能优化是三峡水库消落带植被恢复和生态功能重建的重要任务。     

国产柽柳科3属6种植物营养枝的解剖观察

对国产柽柳科3属6种植物(琵琶柴、沙生柽柳、山川柽柳、多枝柽柳、刚毛柽柳、疏花水柏枝)营养枝解剖结构的比较研究表明：其当年生营养枝在表皮是否具毛、皮层细胞的形态结构、维管束排列方式、形成层的发生、髓部面积及内含物等性状上存在差异,并根据这些差异列出了分属检索表。所选6种植物生态型各不相同,其中琵琶柴为地带性超旱生小半灌木,柽柳为非地带性的潜水性旱、中生灌木,疏花水柏枝为湿、中生灌木。通过比较这6种植物的解剖结构,发现随着生境由湿生向旱生变化,营养枝解剖结构也发生了相应的变化,并与生境形成了良好的适应。     

三峡库区水位调度对消落带生态修复中物种筛选实践的影响

三峡库区消落带形成后面临多个生态学问题, 对消落带进行生态修复的实践是解决这些问题的关键。筛选物种是生态修复的关键, 但多年的群落学观察结果与采用模拟淹水试验、短期定位观测等方法所获结果不一致。产生这种差异的主要原因是许多模拟淹水试验方案在淹水季节性、水淹周期和水淹深度等方面的设计与三峡库区实际调水节律不一致。对重庆忠县4年的水位变化记录进行整理分析发现, 实际调水节律与理论调水方案之间差异巨大; 海拔146、152、158、164、170和176 m处, 非生长季淹水时间分别为294、266、223、167、101和0天, 生长季淹水时间分别为68、20、11、1、0、0天。海拔164 m以下, 出现生长季频繁淹水胁迫。目前许多模拟淹水试验方案只考虑生长季短期浅淹胁迫, 而未考虑非生长季长期深淹胁迫。研究表明生长季淹水和非生长季淹水、深淹和浅淹胁迫对植物适应性的影响有明显差异。模拟淹水试验仅考虑一次淹水过程, 不足以反映种的长期适应性。并且, 模拟淹水试验仅考虑了种的水淹耐受性, 而未考虑现实生境中的种间关系和群落组配过程。因此, 模拟淹水试验对物种筛选实践的指导意义有限。在未来进行物种筛选时, 需重视: 1)非生长季淹水胁迫下物种适应机制; 2)植物出露后的恢复生长、扩展和拓殖能力; 3)消落带形成多年后, 植物群落调查、实地种植植物的长期观察。根据消落带不同区域受水淹胁迫的程度, 筛选反映植物生活史对策的关键功能性状, 并进行植物功能型组划分, 以研究消落带不同区域物种分布、种群和群落动态、景观格局规律, 这对于消落带生态修复实践具有重要的指导意义, 是今后三峡库区消落带生态系统研究的一个发展方向。     

Species-level phylogeographical history of Myricaria plants in the mountain ranges of western China and the origin of M. laxiflora in the Three Gorges mountain region

Myricaria species in China occur mostly in the major high-altitude mountain areas in and around the Qinghai-Tibetan Plateau. The one major exception to this is M. laxiflora which is restricted to the Three Gorges mountain region. In this study, we investigate species-level phylogeographical patterns of Myricaria species in western China and the origin of M. laxiflora . The results show that most chloroplast haplotypes are species-specific, except for one haplotype which is shared by three widespread species. Higher haplotype diversity within the Qinghai-Tibetan Plateau region supports the hypothesis that the Himalayas are the centre of origin for Myricaria . The phylogeny of Myricaria was geographically structured, and an estimated Bayesian chronology suggested the main divergence events occurred during the Late Pliocene and Early Pleistocene (~1.46–2.30 million years ago). The overall phylogeographical pattern was characterized by vicariance events and regional demographical expansion, reflecting a major influence of geological and climatic events on the evolution of Myricaria species. Our data suggest that M. laxiflora has an ancient origin, but has experienced recent population expansion through the Three Gorges Valley. The origin of M. laxiflora was estimated to be during the Early Pleistocene but its demographical expansion was more recent at about 0.015 million years ago. This highlights the unique phylogeographical history of the Three Gorges mountain region, and the deep imprint of the watercourse connections of the Yangtze River Valley on the phylogeographical structure of the species in this region.     

三峡库区消涨带特有濒危植物丰都车前Plantago fengdouensis的迁地保护

丰都车前(Plantago fengdouensis)为近年在三峡库区消涨带发现的一特有植物。通过多年的调查,发现该种仅分布于重庆市忠县、丰都县和巴南区等3个长江江心岛上,总共290株。随着三峡水库的逐步蓄水,丰都车前的自然分布区将于2006年全部水淹,使其成为因三峡工程建设而导致自然生境和野生居群全部毁灭的唯一的草本植物。为保护这一即将野外灭绝的稀有植物,在对其地理分布、生态学和群落学调查的基础上,对其形态特征、年生长周期和生殖值与同属植物车前(P.asiatica)和北美车前(P.virginica)进行了调查、试验和比较研究,表明丰都车前果期长、种子不适宜长距离传播和生殖值低以及长江水淹干扰是其狭域分布和数量稀少的主要原因。同时探讨了其迁地保护策略,并提出了下一步的研究和保护建议。     

Reproductive allocation,seed dispersal and germination of <Emphasis Type="Italic">Myricaria laxiflora</Emphasis>, an endangered species in the Three Gorges Reservoir area

Myricaria laxiflora is an endangered plant that grows in the flood zone along the Yangtze River in the Three Gorges area from 70 m to 155 m above sea level. To understand the spatial distribution patterns of the species and to provide information for developing conservation strategies, we used field surveys to study its seed reproduction and dispersion, and used growth chambers to study seed germination. Results showed that M. laxiflora produced many flowering branches, inflorescences and seeds. Seeds were very small and output was high although biomass allocation to reproduction was low (∼4%). Reproductive allocation was strongly correlated with the biomass of stems and leaves. Seeds were dispersed either by the wind or the river current. Wind-dispersed seeds usually settled within 25 m from parent plants leading to a clumped distribution of individuals in populations. Water-dispersed seeds often landed and established on strands of firth where the fine sediment and gentle sloping were available. Seedlings that emerged from water-dispersed seeds were distributed along the water flood line. The life-span of M. laxiflora seeds was about 7 days. Seeds could germinate within 24 h when they absorbed adequate amounts of water. Soil water content was a key factor limiting the establishment ability of M. laxiflora. Experiments showed that the minimum soil water content for germination to occur was 10% on sand or 17% on sandy soil substrates, and the optimal conditions were on saturated soils. The water content of sandy soils on the riverbank was lower than 10% in autumn, the dry season, and seeds were able to germinate only on sandy beaches that were intermittently inundated by the fluctuating river current. These characteristics of seed dispersal and germination limit the ability for M. laxiflora to expand its distribution. These results provide information essential for the conservation and reintroduction of this endangered species.     

三峡库区消涨带特有濒危植物丰都车前Plantago fengdouensis的迁地保护

丰都车前(Plantago fengdouensis)为近年在三峡库区消涨带发现的一特有植物。通过多年的调查,发现该种仅分布于重庆市忠县、丰都县和巴南区等3个长江江心岛上,总共290株。随着三峡水库的逐步蓄水,丰都车前的自然分布区将于2006年全部水淹,使其成为因三峡工程建设而导致自然生境和野生居群全部毁灭的唯一的草本植物。为保护这一即将野外灭绝的稀有植物,在对其地理分布、生态学和群落学调查的基础上,对其形态特征、年生长周期和生殖值与同属植物车前(P.asiatica)和北美车前(P.virginica)进行了调查、试验和比较研究,表明丰都车前果期长、种子不适宜长距离传播和生殖值低以及长江水淹干扰是其狭域分布和数量稀少的主要原因。同时探讨了其迁地保护策略,并提出了下一步的研究和保护建议。     

Can the soil seed bank contribute to revegetation of the drawdown zone in the Three Gorges Reservoir Region?

The drawdown zone of the Three Gorges Reservoir Region was assumed to be completely formed in 2009 and the water level would range from ~145 m in flood season (summer) to ~175 m during non-flood season (winter). The soil seed bank is an important propagule source for vegetation restoration. In order to evaluate the potential of the soil seed bank to revegetate the drawdown zone of this region, we examined the quantitative relationships between the germinable soil seed bank and the established vertical and horizontal vegetation patterns. A total of 45 soil samples at four sites was collected to examine seed bank density, species richness, and composition using the seedling-emergence method. Forty-five species (from 20 families) germinated from the soil seed bank, and the average seed density was 4578 m⁻². The seed bank was dominated by annual plants, suggesting reestablishment of some above-ground species was plausible. However, most established woody plants and perennials were absent from the seed bank indicating a low probability of reestablishment for non-annuals through the seed bank. Thus, due to low species compositional similarity to extant vegetation and the dominance of annual plants, the soil seed bank had a low potential to restore pre-dam vegetation in the drawdown zone of the Three Gorges Reservoir Region, but its potential as a propagule source should be considered regarding the management of the drawdown zone for vegetation cover.     

三峡库区水库蓄水对崖沙燕种群的影响

2003年三峡水库蓄水至139m高程,在蓄水前(2000年)和蓄水后(2003～2006年)对长江主河道尾水点所在的丰都至忠县江段和上游河道区域,以及支流河道的巫山县大宁河139m水位尾水点的崖沙燕(Riparia riparia)种群分布和数量进行了调查。结果表明,在水库蓄水至139m之后崖沙燕的种群数量明显减少。影响崖沙燕种群数量的关键因素是丧失繁殖地。随着三峡大坝工程的全面竣工和运行,三峡库区的崖沙燕有可能将会成为少见物种。     

High interpopulation genetic differentiation and unidirectional linear migration patterns in Myricaria laxiflora (Tamaricaceae), an endemic riparian plant in the Three Gorges Valley of the Yangtze River

Myricaria laxiflora is restricted to the riverbanks of the Yangtze River valley and will be completely lost owing to the construction of the Three Gorges Dam. Genetic diversity and structure of nine natural and one ex situ populations were investigated using amplified fragment length polymorphisms (AFLPs). A moderate level of gene diversity was found in natural populations, while the ex situ population had the highest. The F statistics calculated by different approaches consistently revealed a high genetic differentiation among natural populations, contributing >45% of the total gene diversity. The Bayesian-based analysis differentiated nine independent populations in accordance with the sites sampled. Estimates of gene flow by F(ST) and coalescent-based simulation analysis indicated a restricted recurrent gene exchange among populations (Nm = 0.290-0.401), whereas genetic distance-based clustering and coalescent-based assignment analyses revealed significant genetic isolation among populations. The migration pattern in M. laxiflora is best explained by a classical metapopulation model, but with a unique unidirectional direction underlined by hydrochoric force that drove dispersal of seeds and propagules from upstream toward downstream populations. Previous efforts in preserving genomic integrity in ex situ conservation were evaluated, and the results provide valuable information to formulate conservation guidelines for successfully reintroducing M. laxiflora to the wild.