围封沙质草甸土壤种子库与幼苗库的特征

采用野外定点取样和萌发实验相结合的方法,研究了科尔沁沙地围封沙质草甸土壤种子库和幼苗库的特征.结果表明:土壤种子库总密度为13854±1651有效种子数/m2,而幼苗库的总密度为808±164株/m2,仅为土壤种子库总密度的6%,土壤种子库与幼苗库总密度之间存在显著的差异 F=36.0,n=219,P<0.001 .土壤种子库与幼苗库的植物种数分别为37和44,其中一、二年生草本植物分别占种子库与幼苗库植物种数的62%和50%,而多年生草本植物所占的比例分别为24%和41%,灌木所占的比例很小,分别为14%和9%.土壤种子库与幼苗库种类组成上的相似性系数为0.667,表现出较小的异质性.土壤种子库密度与幼苗库密度之间存在显著的相关性,其间关系可用三次曲线来描述.     

科尔沁沙质草地放牧和围封条件下的土壤种子库

该文研究了科尔沁沙质草地在放牧和围封条件下土壤种子库密度、组成及其与地上植被的关系。结果表明:1)放牧草地植物种数22种,围封草地植物种数30种,围封使土壤种子库植物种数增加了36%;2)放牧草地土壤种子库密度为16 149±1 900有效种子数·m^-2, 围封草地土壤种子库密度为20 657±3 342有效种子数·m^-2,比放牧草地增加了28%。放牧和围封草地种子库组成密度均以一年生植物为主(分别占99%和98%的比例),多年生植物所占的比例很小;3)放牧草地种子库的Shannon-Wiener指数和丰富度指数分别为0.836 3和4.954 9,明显小于围封草地的0.968 2和7.226 0,表明自由放牧导致物种多样性下降;4)放牧和围封草地土壤种子库密度与地上植被密度均存在显著的相关性(p<0.001)。表明了随着土壤种子库密度的增加, 地上植被密度随之增加,放牧草地地上植被密度78%的变异可归结为土壤种子库密度的变异, 而围封草地地上植被密度58%的变异可由土壤种子库密度的变异来解释。     

放牧和围封条件下克氏针茅草原土壤种子库的比较

应用幼苗萌发法对比研究了我国北方农牧交错区克氏针茅(Stipa krylovii)草原在放牧和围封条件下土壤种子库的差异。围封样地的土壤种子库中记录有16个物种,其中禾草类6种,非禾草类10种;若以生活型划分,则全部为多年生植物;若以单子叶或双子叶植物划分,则单子叶植物9种,双子叶植物7种。放牧样地的土壤种子库中记录有13个物种,其中禾草类4种,非禾草类9种;多年生植物12种,一二年生植物1种;单子叶植物5种,双子叶植物8种。放牧样地土壤种子库的密度为(3 664±1 087)粒·m^-2,围封样地土壤种子库的密度是(5 139±1 848)粒·m^-2,差异显著。采用Sorensen指数计算土壤种子库与地上植被的物种相似性,围封样地和放牧样地分别是0.711 1和0.611 1。两个地点的全部种子中, 81.0%属于冷蒿(Artemisia frigida)、克氏针茅、星毛委陵菜(Potentilla acaulis)、糙隐子草(Cleistogenes squarrosa)和砂韭(Allium bidentatum)5种优势植物,16.2% 属于二裂委陵菜(P. bifurca)、菊叶委陵菜(P. tanacetifolia)、猪毛蒿(A. scoparia)、冰草(Agropyron cristatum)和羊草(Leymus chinensis)5种常见植物,而其余9种植物的种子数只占2.8%。此外,通常作为优良牧草的豆科植物的种子数仅占0.6%。上述结果表明,在放牧条件下由于土壤种子库中一些重要物种的缺失或数量很少以及极不均匀的分布,可能会降低退化克氏针茅草原的自然恢复速度。我们建议采取补播这些重要物种并结合其它恢复措施来加快退化克氏针茅草原的恢复进程。     

荒漠草原区4种植物群落土壤种子库特征及其土壤理化性质

土壤种子库作为地上植被更新的潜在种源,在植被自然恢复和演替过程以及生态系统建设中起着重要作用。以宁夏盐池县荒漠草原区4种植物群落为研究对象,通过对封育16年后植物群落土壤理化性质的变化与其土壤种子库的特征之间的关系的探讨,揭示荒漠草原植物群落的土壤种子库分布特征和演替趋势,以及土壤质量的改变如何影响土壤种子库特征。研究结果表明：（1）不同植物群落土壤种子库物种组成及种子密度不同,同一物种在不同植物群落土壤种子库中出现时种子密度也存在差异;禾本科、菊科、藜科植物种在4种植物群落土壤种子库中出现比例均较高,分别占到26.19%、21.43%和19.05%,占总物种数的66.7%;灰绿藜、冰草、碱蓬在4种植物群落土壤种子库中均有出现。（2）4种植物群落土壤种子库中多年生植物和一年生植物种子居多,灌木、半灌木植物种较少。（3）4种植物群落土壤种子库中物种数和种子密度均表现为：芨芨草群落 > 苦豆子群落 > 油蒿群落 > 盐爪爪群落;且随着土层的加深,4种植物群落土壤种子库中物种数和种子密度均呈递减趋势。（4）4种植物群落土壤种子库中Shannon-Wiener指数、Simpsin指数、Pielou指数和Patrick指数均表现为芨芨草群落 > 苦豆子群落 > 油蒿群落 > 盐爪爪群落。此外,芨芨草群落土壤种子库与油蒿群落土壤种子库相似性最高,油蒿群落与盐爪爪群落的最低。（5）土壤种子库物种多样性特征指数与土壤pH、含水量、碱解氮呈正相关,与土壤电导率呈负相关,其中土壤pH和电导率对种子库物种多样性的影响较大。荒漠草原封育以后,土壤种子库中植物种数、种子密度和物种多样性均呈增加趋势,且以多年生植物和一年生植物种子居多;禾本科和豆科植物的物种数和种子密度大于菊科和藜科,这表明围封后牧草品质改善,植物群落正向演替。     

塔里木河下游不同退化区地表植被和土壤种子库特征

对塔里木河下游不同退化程度的4个典型断面进行了植被和土壤种子库的取样调查,采用种子萌发试验研究了不同退化区植被和土壤种子库的特征,结果表明:(1)塔里木河下游地表植被表现为严重的逆行演替,具体体现为胡杨林都为过熟林,几乎没有胸径在10cm以下的幼林;植被盖度、密度和多样性指数均维持在一个较低的水平上;随退化程度不断加重,地表植被中草本植物的相对密度、相对盖度和相对频度逐渐降低,而灌木和乔木的相对密度、相对盖度和相对频度逐渐增加;(2)研究区土壤种子库的基本特征是:土壤种子库种类贫乏、密度低、多样性指数和相似性系数不高;(3) 随退化程度的加重,土壤种子库物种数不断减少、密度明显下降、优势种组成趋于单一、表层种子库比例升高、1年生草本植物占优势逐渐向多年生草本植物和灌木植物转变及土壤种子库物种组成与地上植被物种组成上差异显著.     

腾格里沙漠东南缘苔藓结皮对荒漠土壤种子库的影响

对腾格里沙漠东南缘沙坡头人工植被区和天然植被区苔藓结皮种子库进行了研究.结果表明,土壤种子库密度随着苔藓结皮的发育呈现增加的趋势,天然植被区是24年生人工植被区的3.4倍.种子库中共发现12种植物种子,分属于6科,其中1年生草本植物占70%以上.人工植被区未发现有多年生草本的植物种子,天然植被区多年生草本占20%,半灌木植物在人工植被区和天然植被区分别占20%和10%.人工植被区土壤种子库物种丰富度指数相对较低,而天然植被区物种丰富度指数是人工植被区的2倍;人工植被区土壤种子库物种多样性指数随着结皮的发育略有下降,天然植被区的多样性指数最高,为0.693;人工植被区土壤种子库物种相似性指数为1,相对较高,而人工植物区与天然植被区的物种相似性指数为0.4.苔藓结皮的出现增加了地表粗糙度,有利于对种子的捕获,同时显著地改善了土壤环境,有利于更多植物的定居.     

河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响

采用种子萌发法,研究了河水漫溢对塔里木河下游荒漠河岸林地表植被与土壤种子库的影响.结果表明：塔里木河下游漫溢区地表植被分属8科13属14种,非漫溢区为10科21属26种植物;与非漫溢区相比,漫溢区地表植被中出现了一些浅根系和喜湿的草本植物;漫溢区单位面积物种数、植被盖度、植株密度、物种多样性指数和丰富度指数均比非漫溢区有明显增加.漫溢区土壤种子库中有物种19种,比非漫溢区增加了5种;漫溢区土壤种子库总密度比非漫溢区增加了3.94倍;与非漫溢区相比,漫溢区1年生草本植物种子的比例增加了23.07%,而灌木植物种子比例减少了20.99%;多年生草本的变化则不明显;河水漫溢提高了土壤种子库的生物多样性.漫溢区和非漫溢区土壤种子库与地表植被的共有物种分别为18和9种,土壤种子库与地表植被的相似性系数分别为0.842和 0.667.     

松嫩平原碱化草甸两个群落土壤种子库动态

对松嫩平原碱化草甸中星星草 羊草群落和星星草群落土壤种子库组成的季节动态进行了研究.结果表明:在4-9月,2个群落的土壤种子库均以多年生草本植物为主,星星草 羊草群落共出现12种,而星星草群落为10种,并均以星星草占最大比例,分别为66.8%～92.9%和75.3%～97.7%.种子库相似性系数在6月最大.星星草 羊草群落种子库密度在7月份最大,为(26 560.0±7 256.9)粒·m-2,星星草群落在8月最大,为(25590.0±6 443.7)粒·m-2;而2个群落的物种多样性指数和均匀度指数则分别在7月和8月最小.     

科尔沁草甸草地放牧和割草条件下土壤种子库研究

研究了科尔沁沙地草甸草地在放牧、割草两种利用方式下的土壤种子库的大小、组成及其与地上植被的关系．结果表明,在自由放牧下,土壤种子库密度为6158±1647粒·m^-2,在割草利用下,土壤种子库密度为8312±2540粒·m^-2．放牧干扰下,种子库组成以矮小、短命的一年生植物为主,其中一二年生植物占81．66％,占比例最大的前4种植物分别为虎尾草(38．55％)、灰绿藜(15．42％)、毛马唐(14．95％)和狗尾草(9．83％),多年生植物种子密度仅为1129±302粒·m^-2;割草干扰下,一二年生植物占68．08％,其中狗尾草占52．7％;而割草地多年生植物种子密度为2653±811粒·m^-2．放牧地土壤种子库密度与地上植物相关不显著;割草地土壤种子库密度与地上植物多度显著相关(r=0．76,P<0．01)．放牧地种子库的Shannon—Wiener指数、丰富度指数分别为2．96和2．98,明显小于割草地的3．10和5．09,表明自由放牧更易使物种多样性下降．     

石羊河中游沙漠化逆转过程土壤种子库的动态变化

在石羊河中游,应用空间代替时间的方法,选择流动沙丘以及封育恢复5a、15a和25a的沙漠化逆转过程序列,研究了沙漠化逆转过程土壤种子库的变化特征。结果表明:石羊河中游沙漠化土地土壤种子库由4科12种植物组成,种子库主要分布于表层0-5cm。在沙漠化逆转过程中,土壤种子库物种数趋于增加,物种组成以1年生草本植物占优势逐渐向多年生草本植物和半灌木植物转变;种子库密度、表层土壤种子比例、物种多样性指数、与地上植被的相似性呈现先增大后降低趋势;沙漠化土地生态恢复间隔的时间越长,土壤种子库间的相似性程度越低;沙漠化土地与地带性植被区种子库的相似性逐渐增大,但是恢复25a沙漠化土地也仅达到0.36。研究认为,沙漠化逆转过程也是沙漠化土地土壤种子库向地带性植被土壤种子库演变的过程,而且是一个十分缓慢的过程,该研究有助于丰富干旱区土壤种子库的理论和指导干旱内陆河流域沙漠化土地的生态恢复实践。     

Ectogenesis and the case against the right to the death of the foetus

Ectogenesis, or the use of an artificial womb to allow a foetus to develop, will likely become a reality within a few decades, and could significantly affect the abortion debate. We first examine the implications for Judith Jarvis Thomson’s violinist analogy, which argues for a woman’s right to withdraw life support from the foetus and so terminate her pregnancy, even if the foetus is granted full moral status. We show that on Thomson’s reasoning, there is no right to the death of the foetus, and abortion is not permissible if ectogenesis is available, provided it is safe and inexpensive. This raises the question of whether there are persuasive reasons for the right to the death of the foetus that could be exercised in the context of ectogenesis. Eric Mathison and Jeremy Davis have examined several arguments for this right, doubting that it exists, while Joona Räsänen has recently criticized their reasoning. We respond to Räsänen’s analysis, concluding that his arguments are unsuccessful, and that there is no right to the death of the foetus in these circumstances.     

On the diversity of the Cladocera in the tropics

The mythical concept of an impoverished tropical cladoceran fauna is refuted. On a planetary scale, around half of the cladoceran species presently known occur exclusively in the tropics-subtropics, often with considerable restriction to particular geographical subzones. On a regional (political) scale, the situation is often unclear because of the continued fragmentary nature of studies, and because political units are not a good basis for biogeographical comparisons. At the finest level of resolution (lake-perlake comparisons), there appears to be an upper limit of c. 50 cladoceran species per individual lake. No significant difference between lakes in the temperate zone and in the tropics could be established here. Daphnia is largely absent from the tropics, but is replaced by more Sidids, Moinids, and Bosminids, such that the average cladoceran community in the limnetic zone of a tropical lake is not characterized by less species but rather by lower population densities. This, in turn, is considered a consequence of higher prevalent predation levels in the tropics.     

Tubular networks in the terminal endings of the visual receptor cells in the human,the monkey,the cat and the dog

Summary A tubular network was found in the terminal endings of the visual receptor cells in the human, the monkey (Macaca mulatta), the cat and the dog. These tubules are arranged in close groups in the vicinity of the synaptic lamellae and the invaginated dendrites. According to the form, diameter, density of the tubules and to the consistence of the network formed by them one can distinguish at these places an initial type (type I), a transitory (type II) and a vesicular one (type III). In the the type III branching, bizarre forms are frequent. The diameter of all the tubules reaches 500–600 Å, their density and walls being the same as in the synaptic vesicles.Similar networks also occur in the axons of the visual receptor cells of the monkey.

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Zusammenfassung In den Endigungen der Photorezeptorzellen von Mensch, Affe (Macaca mulatta), Katze und Hund kommen aus Tubuli bestehende Komplexe vor. Organellenartig in geschlossenen Gruppen angeordnet, liegen sie in Nähe der synaptischen Lamellen und der invaginierten Dendriten. An diesen Stellen kann man nach Form, Durchmesser, Dichte und Konsistenz der von den Tubuli gebildeten Komplexe drei Typen unterscheiden: 1. einen initialen (Typus I), 2. einen Übergangstypus (Typus II) und 3. einen vesiculären Typus (Typus III). In letzterem kommen häufig verzweigte, bizarre Formen vor. Der Durchmesser sämtlicher Tubuli erreicht 500–600 Å. Ihre Dichte und ihre Wand gleicht denen der synaptischen Vesikel.Ähnliche Komplexe fanden wir auch in den Axonen der Photorezeptorzellen vom Affen.

     

Assessing the Physiological State of the Fucoids from the Barents Sea Littoral by the End of the Polar Night

Methods of amperometry and potentiometric titration were used to follow dark respiration (DR) and apparent photosynthesis (AP) in the fucoids Ascophyllum nodosum (L.) Le Jol, Fucus vesiculosus L., and F. serratus L. from the Barents Sea littoral by the end of the 40-day-long polar night. The macroalgae were shown to manifest species-specific low rates of photosynthesis and respiration. However, in spite of their low photosynthetic status due to the effects of subzero temperature and prolonged low or zero illumination, the macroalgae have been able to restore DR and AP to the initial level already by the day 9; the ability to restore AP depended on the level of illumination. The study of the changes in the carbonate–bicarbonate system in the light and darkness demonstrated that the macroalgae grown in darkness, in contrast to those grown in twilight, could absorb bicarbonate in darkness; however, they lost this capacity after two-day-long illumination at an irradiance of 7 mol/(m² s). Bicarbonate uptake in darkness and the capacity to restore the systems of photosynthesis and respiration in fucoid cells are discussed in the context of algal energy metabolism under the polar night conditions.     

Arranging the elements of the potassium channel: the T1 domain occludes the cytoplasmic face of the channel

The voltage-gated potassium channel is currently one of the few membrane proteins where functional roles have been mapped onto specific segments of sequence. Although high-resolution structures of the transmembrane portions of three bacterial potassium channels, the tetramerization domain and the cytoplasmic ball are available, their relative spatial arrangement in mammalian channels remains a matter of ongoing debate. Cryo-electron microscopic images of the six transmembrane voltage-gated Kv channel have been reconstructed at up to 18 Å resolution, revealing that the T1 domain tetramerizes and is suspended below the transmembrane segments. However, the resolution of these images is insufficient to reveal the location of the third piece of the puzzle, the inactivating ball domain. We have used the aberrant interactions observed in a series of chimæric channels to establish that an assembled T1 domain restricts access to the cytoplasmic face of the channel, suggesting that the N-terminal ball and chain may be confined in the space between the T1 domain and the transmembrane portion of the channel.     

Separation of the pineal vesicle from the wall of the third ventricle during the post-hatching development of the chicken

Summary According to light- and electron-microscopic observations the pineal organ of the 3-day-old chicken consists of a prominent end vesicle and a tapering parenchymal stalk. During this stage the pineal lumen is in open communication with the third ventricle. However, in the 40-day-old chicken, which still possesses a well-developed end vesicle, the proximal portion of the pineal stalk displays regressive changes leading to local fragmentation. At this stage the pineal stalk is reduced, and the pineal lumen is missing. In 1-year-old chickens the parenchyma of the proximal portion of the stalk is further diminished, and in 3-year-old domestic fowl is completely displaced by bundles of collagenous fibers, only some nerve fibers being present. This post-hatching pineal development may reflect the sequence of changes leading from pineal sense organs to pineal glands.This work was supported by a grant-in-aid for Scientific Research from the Ministry of Education, Science and Culture of Japan     

On the Dependence of the Quadratic Risk of the Classical Predictor and the Prediction-Horizon

When constructing predictors on the basis of the linear model of time series of various indicators often the question arises on the dependence of forecasting accuracy and the changing prediction horizon. The dependency of the quadratic risk of the classical predictor and the time horizon is considered.     

中国植物区系与其它地区区系的联系及其在世界区系中的地位和作用

基于吴征镒将中国全部种子植物３２３８个属的分布区划分为１５个大类型和３４个变型的基础上,简要地讨论了中国植物区系与其它地区区系的联系,以及它在被子植物起源方面的作用。主要论点如下：（１）与热带亚洲区系的联系。这种联系主要通过第７类型（热带亚洲分布）及其５个变型来体现的。本文列举了１０个科,龙脑香料、狭义隐翼科、交让木科、五隔草科、五列木科、肉实树科、心翼果科、八宝树科、兰花蕉科和四数木科,来说明这