鄂尔多斯草地退化过程中植被地上生物量空间分布的异质性

应用地统计学方法分析研究了鄂尔多斯草地荒漠化过程中植被地上生物量空间分布的异质性。发现从本氏针茅(Stipa bungeana)、本氏针茅 油蒿(Artemisia ordosicn)、油蒿、油蒿 牛心朴子(cynanchum komarovii)、牛心朴子群落的5个退化系列群落中,植被地上生物量空间格局异质化程度及其相关范围变化非常明显。变异函数的基台值(C0 C)在5个退化群落中的变化表明,在本氏针茅群落中,植被地上生物量空间分布异质性较低(0．48),本氏针茅 油蒿群落增强(19．47),油蒿群落显著增强(1522),油蒿 牛心朴子群落减弱(171．6),牛心朴子群落显著减弱(4．164)。变异函数的相关范围(A0)表明,在本氏针茅群落空间相关范围较小(53．9cm),本氏针茅 油蒿群落增加(77．8cm),油蒿群落减小(51．7cm),油蒿 牛心朴子群落增加(62．9cm),牛心朴子群落增加(94．6cm)。空间变异比分析表明,由空间自相关因素引起的空间异质性占主要部分(74．2％～80．7％)。空间分布格局图(Kriging map)分析进一步显示,退化群落中植被地上生物量格局变化显著。从本氏针茅群落退化到油蒿群落的中度荒漠化过程中,植被地上生物量空间分布的异质性的增强。由油蒿群落退化到牛心朴子群落的严重荒漠化过程中,植被地上生物量空间分布的异质性减弱。     

基于植物分布地形格局的植物功能型划分研究

提出基于植物分布的地形格局划分植物功能型（ＰＦＴｓ）的思路, 并以位于中国亚热带北部的大老岭地区为研究区域进行案例研究。通过大量的森林群落调查获得该地区５５种主要的常绿阔叶树在不同地形部位群落中的数量特征：采用去势典范对应分析（ＤＣＣＡ）方法：１．海拔、坡面、坡形、坡位、坡向、坡度等６个地形特征指标与群落生境的热量、水分和光照条件的关系;２．５５种植物在多维地形梯度上的分异格局。然后利用排序得分对     

陕西子午岭生态因素对植物群落的影响

为探讨生境对植被格局分布的影响,对黄土高原马栏林区60块样地进行植被学调查的基础上,采用17个环境指标刻画植物群落的空间位置、地形和土壤特征;利用双向指示种分析(TWINSPAN)划分了该区不同演替阶段的植物群落类型;利用前向选择法(forward selection)及Monte Carlo检验对不同演替阶段植物群落物种组成影响显著(p＜0.05)的环境因子进行筛选;利用去势典范对应分析(DCCA)排序方法分析不同演替阶段植物群落分布格局与环境的关系;利用偏典范对应分析(partial CCA)定量分离环境、空间及其交互作用对植被格局总体变异的影响.结果表明:(1)马栏林区的植物群落可划分为13个类型,分别属于4个不同的演替阶段;(2)对演替初期阶段群落影响显著的环境因子是土壤含盐量和碱解氮,对演替过渡阶段群落影响显著的环境因子是海拔和腐殖质厚度,对演替亚顶级阶段群落影响显著的因子是海拔、坡向、枯落物厚度、腐殖质厚度和pH值,而对演替顶级阶段群落分异影响显著的因子是海拔、坡向、pH值和速效磷;(3)不同演替阶段群落的生态学特性和分布规律与环境空间的生态梯度格局吻合较好;(4)随着演替的进行,环境因子单独对植物群落的影响越来越大,而样地位置单独作用和样地位置与环境因子的交互作用之和越来越小.     

三峡大老岭森林物种多样性的空间格局分析及其地形解释

在对三峡大老岭地区森林的大量群落样方调查基础上,研究地形因子和取样尺度对群落不同层次α多样性水平及其空间格局的影响。结果表明：①受地形、人为或自然干扰的影响,大老岭森林群落的α多样性存在海拔１０００ｍ以下、海拔１１００￣１７００ｍ和活拔１７００ｍ以上３段不同的水平与变化特征;②对海拔１０００ｍ以上样方群落的１６种多样性指数的ＤＣＣＡ分析表明,群落乔、灌、草各层的多样性在多维地形因子梯度上表现出不同     

丹江口水库水滨带植物群落空间分布及环境解释

探讨了环境因素对丹江口水库(南水北调中线水源地)水滨带植物群落空间分布的影响。通过对水滨带植物群落和环境因素的实地调查,用双向指示种分析(TWINSPAN)对201个水滨带植物群落进行分类;结合地形、土壤和水文因素用除趋势典范对应分析法(DCCA)分析环境因素对水滨带植物群落的影响;并对环境因素的解释能力进行定量分离。结果表明:(1)水滨带植物群落包括7种类型,分别是萹蓄群落、苘麻群落、细叶水芹+狗牙根群落、狗牙根群落、响叶杨-狗牙根群落、杜梨-白刺花-狗牙根群落和侧柏-牡荆-三穗苔草群落;(2)海拔和水淹影响对水滨带植物群落空间分布具有主导作用。海拔升高,水淹影响减弱,植物群落呈现由草本植物群落向木本植物群落变化的格局;(3)土壤因素的解释能力大于地形因素,水文因素的解释能力最小。各类环境因素之间存在交互作用,地形、水文和土壤因素三者间的交互作用最大,地形和土壤因素之间的交互作用最小。环境因素共解释水滨带植物群落空间分布的21.99%,未解释部分为78.01%。结果证明环境对植被的解释能力是由植被的复杂程度决定的,植被越复杂,环境的解释能力越低。     

岷江上游干旱河谷植物群落分布的环境与空间因素分析

为了探讨土壤环境因子对植物群落物种数量、结构格局的影响 ,通过对岷江上游干旱河谷灌丛植被的大量群落学调查 ,采用了群落中 9个土壤特征指标 ,利用去势典范对应分析 (DCCA)排序方法 ,分析了不同群落类型中不同层次的物种数量结构的空间格局 ;定量分离了土壤、空间及其交互作用等因素对不同层次群落格局总体变异的影响。结果表明 :以水分为主导的多种环境因子耦合梯度决定着植物群落结构格局。环境因子对群落的影响程度在不同层次有差异 ,在灌木层中 ,单纯环境因子对植被格局的解释占 2 8.0 2 % ,环境 -空间耦合因子占 8.90 % ,空间因子独立占 10 .69% ,其他因子占 52 .3 9% ;而在草本层中 ,单纯环境因子对植被格局的解释占 2 0 .64% ,而环境 -空间耦合因子仅占 0 .83 % ,空间因子独立占 5.10 % ,其他因子占 73 .43 % ,草本的可解释性远远低于灌木。但无论是灌木层还是草本层 ,在诸多因子中 ,土壤水分始终在影响群落物种数量结构的空间格局分布中起着主导作用     

西双版纳20公顷样地热带森林植被数量分类与排序

为了区分热带森林的群落特征并了解其群落特征与地形因子之间的相互关系,以西双版纳20 hm2森林动态监测样地为研究对象,对样地内500个森林群落样方采用Cluster聚类分析方法进行分类和采用除趋势对应分析(DCA)、典范对应分析(CCA)方法进行排序。结果表明:(1)西双版纳热带森林动态监测样地森林群落分为2个类型:热带季节雨林和热带山地常绿阔叶林;(2)植被类型的划分与CCA排序的结果相吻合,CCA排序轴第一、二轴呈现了海拔和凹凸度的梯度变化,并且两者总体上可以对83.9%的植被分布格局进行解释,表明海拔和凹凸度因子对该地区植被类型的分布起着决定性作用;(3)对优势物种的DCA和CCA排序表明不同物种对地形的要求存在差异,其分布格局同样主要受海拔和凹凸度的影响;(4)聚类分析与DCA和CCA排序的结果,同时表明了该地区森林植被的垂直分布格局。此方法可有效解释植被分布格局与地形之间的内在联系,为热带森林的管理和保护提供科学依据。     

地形对植被生物量遥感反演的影响——以广州市为例

目前植被生物量遥感反演研究中的地形校正主要是校正地形变化对地表反射率的影响,较少考虑地形起伏引起的像元面积与实际地表面积的差异,而这种差异将导致植被生物量估算结果的偏差.在生物量遥感反演的基础上,结合地表面积计算模型和物质守恒定律,建立了生物量地形校正模型,定量分析和讨论了地形起伏对广州市植被类型面积提取和生物量准确估算的影响.结果表明:地形校正前后全市针叶林、阔叶林、草地、灌木林和园地面积分别增加6.18％、3.70％、2.86％、1.92％和1.29％;在综合分析区域生物量遥感反演中的各种不确定性的基础上,建立的各植被类型的生物量模型均具有较高精度,相关系数均接近或者超过0.9,可以满足生物量反演的要求;全市植被生物量呈现出东、北高,西、南低的分布格局,像元实际代表的林地(阔叶林和针叶林)平均生物量为61.86t/hm2,高于珠三角区域生物量平均值,但与亚热带林的顶级群落生物量水平有较大差距,林地生物量还有较大的增长空间;经过校正地形变化引起的像元面积和实际地表面积差异对生物量提取结果的影响后,植被总生物量比校正前增加了5.82％,5种植被类型的总生物量有不同程度的增加,阔叶林、针叶林、草地、灌木林和园地分别增加了7.74％,4.76％、3.34％、2.50％和1.58％.与其它的表面积计算模型相比,利用的像元地表面积模型具有较高的精度,可以满足生物量遥感估算中地形校正的需要.     

黄土丘陵区地形、土壤水分与草地的景观格局

在黄土丘陵区,地形因素和土壤水分是决定草地景观格局的主要因素,同时草地景观格局在不同尺度上影响着景观中的流.地形因素、土壤水分和草地结构在不同尺度上有着密切的联系,研究它们之间的关系对于了解生态系统的过程十分重要.针对黄土高原异质化的草地群落结构,选取黄土丘陵区经过20多年自然封育形成的天然草地,从坡面尺度对景观格局进行了调查研究,在地形因素、土壤水分和草地结构中选取了有代表性的指标14个,用多元统计分析对选取的指标进行了主成分分析和聚类分析.聚类分析将样方分成3种植被类型,不同植被类型的海拔、坡度、20～140cm土壤含水量以及物种丰富度和生物多样性存在显著性差异.相关分析表明：海拔对0～300cm土壤含水量影响显著;海拔对草地群落盖度,坡位、坡向对草地群落的物种丰富度和生物多样性有着重要影响;而草地群落的物种丰富度和生物多样性与0～100cm土层的含水量关系密切.     

三峡大老岭地区主要木本植物分布的地形格局

基于对三峡大老岭地区山地森林群落的深入调查,选择样方乔本层重要值大于１．００的１９０种木本植物,依次根据生活型和植物在群落中的地位分成常绿针叶树种,常绿阔叶树种、落叶阔叶的建群树种、伴生种和珍稀树种共６组,采用ＤＣＣＡ排序分析各组植物种在复合地形梯度上的空间格局特征;然后分别统计常绿或落叶的乔木或藻木４组物种沿具体海拔高度的整体分布特征,研究反映了６个生态种组之间在山地地形上鲜明的格局差异,并显示     

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.     

Feeding the vertebrate retina from the Cambrian to the Tertiary

The retina of the vertebrate eye is metabolically active and requires nutritive support. During the last 540 million years it has evolved into forms as complicated and nutritionally demanding as those found in avian or primate eyes. Diffusion from the choroid is generally able to supply the metabolic needs of thin retinae. However, when the thickness exceeds the limits of diffusion, structures are needed to supplement the vascular supply from the choroid. These supplemental nutritive devices include the choroidal gland, the falciform process and preretinal vascular plexus of fish, the conus papillaris of lizards, the pecten oculi of birds, the intraretinal vessels of mammals and a few novel systems that remain difficult to classify. These vascular systems are among the most variable features of the vertebrate eye. Here, we review classical and recent findings regarding such retinal nutrition systems, propose a three category classification for them based on histologic origins and speculate on the evolutionary forces which drove their development.     

Observations on the permeability of the choriocapillaris of the eye

Summary The choriocapillaris is a fenestrated capillary bed located posterior to the retinal pigment epithelium. It serves as the main source of supply to the photoreceptors, retinal pigment epithelium, and other cells of the outer retina. The permeability of these capillaries to intravenously injected ferritin (MW — approx. 480,000; mol. diam. 11 nm) was examined in the mouse, rabbit, and guinea pig, each of which is characterized by a different type of retinal vascularization. In all three species, the bulk of the ferritin remained in the capillary lumina, where it appeared to be blocked at the level of the diaphragmed fenestrae. Some ferritin was present in endothelial cell vacuoles. The results confirm previous work on the rat choriocapillaris and indicate that the barrier function of the choriocapillary endothelium is present even among species in which the retinal circulation differs significantly.Supported by NIH grant EY03418