从空间分布特征认识珍稀植物领春木的种群动态

领春木(Euptelea pleiosperrnum)系第三纪孑遗植物和东亚特有种,目前已被列为国家Ⅲ级重点保护植物.基于空间定位数据以最近邻体距离统计研究了神农架地区领春木的空间分布特征,比较幼苗(DBH≤2.5cm)、幼树(2.5～7.5cm)和成树(＞7.5cm)各径级(代表各生活史阶段)形成的时间序列上的空间格局差异,进而探讨空间格局与立苗、补员、种内竞争等种群动态过程的相互关系.结果显示,在邻域尺度上,领春木的空间格局呈聚集态;幼苗(或幼树)的大小与其距离最近幼树(或成树)的远近没有相关性,幼树(或成树)周围一定距离以内出现同等大小个体的概率约等于幼苗(或幼树)出现的概率,且幼树与最近幼苗(或成树与最近幼树)的平均距离与幼树之间(或成树之间)的平均最近邻体距离没有显著差异;任意个体的大小、任意个体与相应最近邻体的大小之和与相应的最近邻体距离均为显著的正相关关系,但幼树间的最近邻体距离并不大于幼苗随机死亡产生的最近邻体距离,成树间最近邻体距离也不大于幼苗+幼树随机死亡产生的最近邻体距离.这些结果表明,领春木的聚集分布可能与种子散布、生境异质性对立苗格局的作用有关;已定植的大个体可能不限制其邻域内小个体的布局与生长,但是长期的补员过程与邻体间的相互作用不无关系;邻体间存在一定程度的竞争作用,但是竞争强度并未充分激化至发生距离依赖的死亡.     

PCR快速检测伪狂犬病病毒野毒感染

根据已发表的伪狂犬病病毒(PrV)gE、gI基因的序列,设计并合成了一对引物,以PrV容A株细胞培养毒为模板,筛选最佳反应条件和试剂工作浓度,建立了区分PrV野毒株和疫苗弱毒的鉴别PCR方法。该方法能从PrV容A株(RA)、上海株(SH)、鲁A株(LA)中扩增出一条848bp的片段,但Bartha-K61株没有扩增出该片段。测序结果表明PCR扩增产物和方法的特异性。对正常细胞与其它6种引起猪病毒性疫病相关病毒进行检测,结果均为阴性,没有出现交叉反应。对PrV容A株细胞毒提取物DNA进行检测,其最低检出量为5pg。PCR对感染野毒的发病猪不同组织器官检测发现,淋巴结检出率最高,依次为脾、脑(海马角)、肺、肾、肝等。对2003～2004年期间江苏、浙江、安徽、福建、上海等省市的37个大中型猪场送检的172份病料进行PCR检测病料阳性率为20．34％(35／172),猪场阳性率为40.54％(15／37)。实验结果表明所建立的PCR技术可用于伪狂犬病野毒感染的快速鉴定和流行病学调查。     

Effects of disturbance intensity and frequency on early old‐field succession

Abstract. Early old‐field succession provides a model system for examining vegetation response to disturbance frequency and intensity within a manageable time scale. Disturbance frequency and intensity can interact with colonization and competition to influence relative abundance of earlier and later successional species and determine, respectively, how often and how far succession can be reset. We tested the joint effects of disturbance frequency and intensity on vegetation response (species richness, abundance, canopy structure) during the first six years of succession by clipping the dominant species (D) or all species (T) in spring and fall of each year (S), once per year in summer (Y1), each two years in summer (Y2), or each four years in summer (Y4). Vegetation response reflected disturbance effects on expansion of a later monospecific dominant perennial herb, Solidago altissima, and persistence of the early, richer flora of annuals. A more abundant and taller top Solidago canopy developed on plots clipped each 2 yr or less frequently. Plots clipped yearly or seasonally were richer, but had less abundant, shorter, and differently stratified canopy. Disturbance mediated the relative abundance of early and later successional species; however, frequency and intensity effects were not completely congruent. Persistence of a richer early successional flora increased through the most frequent disturbance (S), and was magnified by disturbance intensity. Disturbance as extreme as clipping all vegetation twice yearly did not cause a drop in species richness, but maintained the early successional community over the first six years of succession. We conclude that clipping disturbance influenced the rate of succession, but the early community could rebound through the range of disturbance frequency and intensity tested.     

Establishment and growth of hawthorn in floodplains in the Netherlands

Dendrochronology was used to assess the influence of soil conditions, elevation and related inundation, climate fluctuations and vegetation cover on the establishment and growth of hawthorn in non-grazed river floodplains. Presence of forest influences the discharge capacity of the floodplain, therefore forest development needs to be considered in management plans. Although ring detection in hawthorn is difficult, clear dynamics in establishment and growth of this shrub species were found. Establishment was mainly influenced by inundation (length and height). The effect of inundation on establishment is location dependent; positive due to transport and deposition of seeds in higher areas, and negative due to drowning of young plants in lower locations. Extreme climatic events were found to influence establishment including a drought in 2003 and relatively low and high precipitation in 2004–2006 and 2007 respectively. These events combined with almost no inundation caused some anomalies in the time series for hawthorn establishment. Once above a certain height, hawthorn is able to withstand various abiotic disturbances occurring in these dynamic river floodplains. Excavated areas are enhancing forest development following hawthorn establishment and therefore these areas should be limited in size (e.g. by deeper and narrower excavations and thus a steeper transition towards the grasslands).     

A 31p and 15N NMR study of the extraction of uranyl nitrate by Di-2-ethylhexyl phosphoric acid

Low temperature ³¹P and ¹⁵N NMR spectroscopy was used to investigate the species forming in the organic layer following the extraction of uranium from nitric acid solutions with di-2-ethylhexyl phosphoric acid. It was found that uranium is extracted from neutral solutions as the 1:2 complex UO₂A₂ regardless of what anion is present. For dilute nitric acid solutions, the uranium is extracted both as associated and mixed nitrato species. As the nitric acid concentration of the aqueous layer increases, the mixed nitrato complex, UO2(NO₃)A·HA, becomes predominant.     

Seed size and shade-tolerance: a comparative analysis of North American temperate trees

Large seed size is a trait associated with plant species of mature, closed habitats, and is thought to supply an ample nutrient reserve necessary for seedling establishment. While this relationship has been shown for annuals and short-lived perennials, it is poorly documented for trees. A comparative method was used to determine whether North American temperate tree species which typically establish in shady conditions have larger seeds than those requiring more open conditions. Both angiosperms (hardwoods) and gymnosperms (conifers) were involved in the study. A significant relationship was found between large seed mass and shade-tolerance for angiosperms, but not for gymnosperms. These contrasting results seem to relate to unique evolutionary opportunities or constraints in different taxa. The absence of a relationship for gymnosperms is discussed in terms of character traits which might prevent seed size selection in response to shade. The finding for angiosperms underlines the importance of the regeneration niche in promoting coexistence among temperate hardwood species through seed size differentiation. Received: 18 March 1997 / Accepted: 26 November 1997     

Host specificity, establishment and dispersal of the gorse thrips, Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), a biological control agent for gorse, Ulex europaeus L. (Fabaceae), in Australia

Sericothrips staphylinus was released as a biological control agent for Ulex europaeus in New Zealand and Hawaii following tests on ca. 80 plant species which showed it was narrowly oligophagous. To determine the suitability of S. staphylinus for release in Australia, further host specificity tests were conducted on 38 species and cultivars of Australian plants. These tests confirmed that S. staphylinus would feed only on U. europaeus in Australia and, following formal approval, was released in Tasmania during January 2001. To develop an optimal release strategy for S. staphylinus under Australian conditions, a field trial based on an earlier New Zealand study was conducted by replicating releases of 10, 30, 90, 270 and 810 adults. Results showed that population growth, reproduction rate and the number of S. staphylinus recovered 14 months after release can be non-linear functions of release size and establishment could be achieved with as few as 10 thrips. As S. staphylinus is easily cultured ca. 250 thrips were chosen as the minimum number for release because, based on a negative binomial model, this release size produced close to the maximum population growth. Surveys in early 2007 recovered S. staphylinus from 80% of 30 sites in Tasmania, the post release period ranging from 1 to 6 years. However, densities were low (<1 thrips/cm of tip growth) with no evidence of visible plant damage. The maximum dispersal range was 180–250 m after 38 months. At all the other sites, dispersal was estimated at less than 120 m. It is possible that S. staphylinus populations are still in the lag phase of their establishment before starting to increase rapidly and disperse. However, the survey results support a recent Tasmanian study which indicated that S. staphylinus is a sedentary, latent species characterised by steady densities and low levels of damage to its host plant. Its efficacy as a biological control agent on gorse may be restricted primarily by ‘bottom up’ effects of plant quality limiting its rate of natural increase and an inability of the thrips to reach large, damaging populations under field conditions.