长白落叶松人工林天然更新幼苗分布格局及其研究方法的比较

长白落叶松是东北东部地区主要造林树种之一．该文研究了55a生长白落叶松人工林天然更新幼苗的空间分布格局．测定了样地内（30m×18m）所有天然更新幼苗的坐标、地径和苗高．在幼苗坐标点图的基础上,进行了23个取样尺度（离散尺度）下的相邻格子法的空间格局分析：采用Poisson分布、负二项分布和正二项分布拟合幼苗的离散分布,方差均值比、Morisita指数和最近邻体法确定了空间分布格局,C-指数、Green指数和负二项参数K值度量了它们的聚集强度．利用更新幼苗的坐标点图,采用地统计学中自々半方差分析方法和空间点格局方法（采用Ripley二次分析法）研究了尺度连续变化条件下更新幼苗空间分布格局和聚集强度的变化并确定了其聚集规模,利用最近邻体法的计算方法分析了更新幼苗的自然定植特点．结果表明：1）更新幼苗所有离散尺度下（样方面积从1m^2到18m^2）均呈聚集分布．连续尺度下,在0—10．5m的半径区间内呈聚集分布,在10．5—12．3m的半径区间内呈随机分布．2）离散尺度下（样方面积从1m^2到18m^2）,聚集强度随尺度的增加而增加．连续尺度下,在0．10．5m的半径区间内,聚集强度随尺度的增加表现出先增加后降低的趋势,在半径（尺度）为4．2m处聚集强度最大．3）此次调查的样地范围内天然更新幼苗呈现聚集状态生长的平均最大聚集斑块（聚集规模）的半径为4．79m．4）天然更新幼苗之间的平均距离为0．30-0．42m,更新幼苗生长在与母树相距2．99—3．26m之外的空间．5）相邻格子法（传统的样方方法）和空间点格局分析法对格局的判别和格局强度的确定基本一致,但是空间点格局分析法能够反映出尺度连续变化条件下格局和格局强度的变化．它与最近邻体法和地统计学方法等以种群分布的坐标点图为数据源的     

秦岭太白红杉种群空间分布格局动态及分形特征研究

采用相邻格子样方法采集数据,应用计盒维数和信息维数研究了太白红杉种群空间格局的分形特征,结果表明,太白红杉种群有较高的计盒维数(1.8087)和信息维数(1.7931),表明其对空间占据程度较高.用分布系数法和Morisita格局指数法检验格局类型,发现不同年龄组太白红杉种群均呈聚集分布.运用Greig-Smith的方法研究格局规模,发现太白红杉种群在128m²和512m²处聚集,不同年龄组在不同规模尺度聚集.以区组分布格局强度(PI)检测聚集强度,发现太白红杉种群格局强度随尺度变化程度较高,个体分布不均匀,随着年龄的增大,其聚集强度呈下降趋势.太白红杉种群的空间分布格局特征是其对严酷生境长期适应的结果.     

祁连山红腹牧草蝗雌雄虫空间格局及关联性

应用地统计学的方法,研究了祁连山北坡石羊河上游,6—10月之间红腹牧草蝗Omocestus haemorrhoidalis(Charpentie)雌雄虫的空间分布格局、动态变化及空间相关性。结果表明:红腹牧草蝗雌雄虫的半变异函数为球状模型与高斯模型,二者空间分布类型相同,均呈聚集分布;随时间的变化均呈现"扩散-聚集-扩散-聚集"的动态特征,7—8月之间雌虫的变化强度明显强于雄虫;二者的模糊贴近度指数在0.53～0.71之间,且指数随红腹牧草蝗的生长呈逐渐增加到减少的变化特征,表明雌雄虫在数量与空间上有较强的跟随关系,且跟随关系随红腹牧草蝗的生长发生明显的阶段性变化。     

基于加权Ripley's K-function的多尺度景观格局分析——以江苏盐城滨海湿地为例

以1987,1992,1997,2002,2007年的遥感影像为例,首次尝试使用加权Ripley's K-function的多尺度格局分析方法,计算了20年来景观异质性在江苏盐城滨海湿地的时间变化和空间分布趋势。通过对研究区的样带划分以及景观类型的点状化处理,建立滨海湿地样带图层和1987—2007年间各类型景观的点格局数据库,从而分析滨海湿地不同类型景观的空间聚集特征变化。基于加权Ripley's K-function的计算表明,在各级空间尺度和时间变化上,各类型湿地的斑块都呈现出空间聚集分布状态,且1987年以来,不同湿地类型的聚集空间特征尺度和空间分布强度均出现了大幅的增减变化,除互花米草滩之外的自然湿地的聚集空间特征尺度和强度都有明显下降甚至少到无法被检测到,而人工湿地却呈现聚集特征尺度和强度的双增长,且该聚集程度有逐渐增强的趋势。分析表明,既考虑样点的空间位置信息又考虑样点分布范围的加权Ripley's K-function方法能很好地表征湿地景观在多尺度上的变异,且与传统空间景观指数等分析方法的结论在一定程度上保持一致。     

苜蓿籽蜂幼虫空间分布型及抽样技术的研究

应用多个聚集度指标和Iwao、Taylor回归分析方法,对苜蓿籽蜂Bruchophagus roddi幼虫的空间分布型进行研究。结果表明其空间分布型为负二项分布,个体间相互排斥,其基本成分的空间分布格局为聚集分布,其聚集是由昆虫行为或环境条件引起的,聚集强度随着种群密度的升高而增加。应用 Iwao抽样模型建立了籽蜂幼虫的田间理论抽样数公式：N=(0.5833/m+2.3370)/D∧2。      

茂兰喀斯特常绿落叶阔叶混交林树种的空间分布格局及其分形特征

分析种群的空间分布格局有助于推断格局形成的潜在生态过程和机制,是生态学研究的重要内容。采用4种格局强度指数(聚块性指数、格林指数、扩散系数和负二项参数)以及分形维数中的计盒维数(D_b)和信息维数(D_i)对贵州茂兰国家级自然保护区亚热带喀斯特常绿落叶阔叶混交林中30种乔木的种群空间分布格局及其分形特征进行了分析,同时分析了不同生长阶段(幼树、中树和成树)空间分布的分形维数变化,比较了2种分形维数与5种种群结构参数和4种格局强度指数间的相关关系。结果表明:(1)30种树种中,除皱叶海桐(Pittosporum crispulum)和油柿(Diospyros oleifera)外,其余28种乔木树种的种群空间分布格局均呈现聚集分布,这种普遍的聚集性与喀斯特生境的高度异质性和种子扩散限制密切相关;(2)30种树种空间分布的D_b值介于0.589-1.870,D_i值介于0.498-1.711。分形维数值越大,表征种群对空间环境的占据利用能力越强,个体空间聚集强度越强,在群落中往往处于优势地位;反之则表明其对环境的占据能力弱,个体聚集程度越低,往往处于伴生地位;(3)从幼树、中树到成树阶段,30种树种空间分布的D_b和D_i平均值呈极显著的降低趋势,这可能与种内和种间的密度制约性死亡效应有关,导致种群随年龄的增加其聚集度和空间占据能力逐渐减弱;(4)相关分析表明,30种树种的种群多度和重要值与D_b和D_i均呈现显著正相关关系,表明种群多度和重要值的变化与种群空间占据能力和聚集程度存在密切关系。4种格局强度指数中,除聚块性指数外,其余3种指数与D_b和D_i值呈现显著或极显著相关性,表明分形维数D_b和D_i值可以用于表征种群空间分布的聚集程度。利用格局强度指数和分形维数准确量化了茂兰喀斯特森林树种的空间分布格局,其结果有助于揭示喀斯特森林群落物种共存的潜在维持机制。     

河北省耕地生态经济系统能值指标空间分布差异及其动因

采用能值理论与地理学研究中的空间自相关分析(ESDA)技术相结合,估算2009年河北省138个县的耕地生态经济系统各项能值指数,在此基础上,重点分析省域范围内耕地生态系统能值指标的空间格局分布规律、特征,从地形地貌、土壤类型、降雨量、耕地集约利用、农业基础设施等方面探讨了空间分布差异原因。结果表明:河北省耕地生态经济系统能值单项指标与综合指标在省域范围呈空间聚集分布,能值综合指标的Moran's I指数较大,聚集特征显著,其大小顺序为EIR> EYR> ELR >ESI,单项指标Moran's I的排列顺序依次为,EMY> EMF> EMR >EMN> EMRI;河北省耕地生态经济系统能值单项指标与综合指标局部空间聚集格局显著,不同能值指标其局部空间分布格局存在差异,主要聚集区为"石家庄-保定-唐山"和"张家口"地区,宏观视角上,能值指标的空间格局分布差异,主要受到地形地貌、土壤类型、年平均降雨量,农业基础设施以及耕地集约利用水平的影响。     

导管三维重构的基本方法

导管是被子植物运输水分和无机盐的管道,它由一串导管分子以穿孔端壁相互衔接而成。关于它在输水过程中的作用,常用的比较方法是通过离析来测定导管分子的长度和直径,或者是通过三切面来观察某一导管分子与邻近细胞的相互关系。由于上述方法所展示的仅仅是某一局部区域中木质部各种组成分子的平面关系或者是某一组成分子的变化模式,所     

木本植物水力学结构之导管长度研究进展

导管作为多数被子植物木质部水分运输的主要通道, 了解其结构及功能对研究被子植物水力学特性及植物对环境的适应性有着重要的作用。导管长度作为导管解剖特征之一, 对水分运输的安全性及有效性有着重要的影响。该文概述了导管长度测量及计算的方法, 导管长度在种内及种间的分布, 导管长度与导管直径的关系, 导管长度与导水率的关系及导管长度对建立栓塞脆弱曲线的影响, 并对未来导管长度的研究工作重点提出了建议: 1)改进灌注物质, 使灌注更加充分且更利于观察、提高计算精度、发展活体动态测量技术; 2)建立导管在植物不同器官及整体的分布网络以及不同生活型、不同地区的导管长度数据库; 3)对导管直径在导管方向的变化, 导管长度与其他导管特性之间的关系进行研究; 4)光学测量建立栓塞脆弱曲线技术的兴起, 可为解决离心机法建立栓塞脆弱曲线的真实与准确与否的争议提供新的方向。更深入地了解导管长度在植物水力功能中担负的角色, 可以为耐旱、抗旱品种选育提供理论基础。     

珠江三角洲林地结构现状及景观梯度分异特征

随着城市化进程加快, 森林生态系统日趋遭到破坏, 进行景观格局研究有利于认识其潜在规律与驱动机制。论文综合运用景观指数与点格局方法, 研究珠三角林地景观的“镶嵌性”和“梯度性”特征, 对珠江三角洲林地结构现状、景观梯度的林地点个数、点密度以及空间聚集特征进行量化分析并探讨林地景观空间分布模式。计算结果表明: 珠江三角洲林地面积较大, 构成了研究区的景观基质。林地点个数和点密度在景观梯度上, 呈正态或偏正态分布; 林地景观在不同空间尺度上都呈聚集分布, 但不同林地类型聚集尺度和空间分布强度不尽相同。在空间分布模式上, 研究区大尺度以有林地基质分布模式为主; 中小尺度下, 不同地域分别呈现出以有林地连片—疏林地呈条带状、有林地基质—灌木林地团块状为主的分布模式。研究结果说明林地景观结构具有尺度依赖性且为层次结构复杂的系统, 印证了景观生态学的尺度效应和等级理论普遍存在, 景观指数和点格局相结合的方法在研究林地景观格局中具有有效性。     

Refilling of a hydraulically isolated embolized xylem vessel: model calculations

When they are hydraulically isolated, embolized xylem vessels can be refilled, while adjacent vessels remain under tension. This implies that the pressure of water in the refilling vessel must be equal to the bubble gas pressure, which sets physical constraints for recovery. A model of water exudation into the cylindrical vessel and of bubble dissolution based on the assumption of hydraulic isolation is developed. Refilling is made possible by the turgor of the living cells adjacent to the refilling vessel, and by a reflection coefficient below 1 for the exchange of solutes across the interface between the vessel and the adjacent cells. No active transport of solutes is assumed. Living cells are also capable of importing water from the water-conducting vessels. The most limiting factors were found to be the osmotic potential of living cells and the ratio of the volume of the adjacent living cells to that of the embolized vessel. With values for these of 1.5 MPa and 1, respectively, refilling times were in the order of hours for a broad range of possible values of water conductivity coefficients and effective diffusion distances for dissolved air, when the xylem water tension was below 0.6 MPa and constant. Inclusion of the daily pattern for xylem tension improved the simulations. The simulated gas pressure within the refilling vessel was in accordance with recent experimental results. The study shows that the refilling process is physically possible under hydraulic isolation, while water in surrounding vessels is under negative pressure. However, the osmotic potentials in the refilling vessel tend to be large (in the order of 1 MPa). Only if the xylem water tension is, at most, twice atmospheric pressure, the reflection coefficient remains close to 1 (0.95) and the ratio of the volume of the adjacent living cells to that of the embolized vessel is about 2, does the osmotic potential stay below 0.4 MPa.     

The role of microtubules in vessel member differentiation inColeus

Summary The role of microtubules in tracheary element formation in cultured stem segments ofColeus has been investigated through the use of the antimicrotubule drug, colchicine. Colchicine treatment of the cultured stem segments produced a dual effect on xylem differentiation. If applied at the time of stem segment isolation or shortly thereafter, wound vessel member formation is almost completely blocked. However, if colchicine is applied after the third day of culture, it does not inhibit differentiation, but instead large numbers of xylem elements are formed which have highly deformed secondary walls. Both effects are related to colchicine's specific affinity for microtubules. In the first case it is shown that colchicine blocks mitosis, presumably by destroying the spindle apparatus, and thus inhibits divisions which are prerequisite for the initiation of xylem differentiation. While, if colchicine is applied after the necessary preparative divisions have taken place, it destroys specifically the cortical microtubules associated with the developing bands of secondary wall, thus causing aberrant wall deposition.Light and electron microscopic analysis of drug-treated cells reveals that the secondary wall becomes smeared over the surface of the primary wall and does not retain the discrete banded pattern characteristic of secondary thickenings in untreated cells. Examination of colchicine-treated secondary walls in KMnO₄ fixed material shows that in the absence of microtubules the cellulose microfibrils lose their normal parallel orientation and are deposited in swirls and curved configurations, and often lie at sharp angles to the axis of the secondary wall band. Microtubules, thus, appear to play a major role in defining the pattern of secondary wall deposition and in directing the orientation of the cellulose microfibrils of the wall. Factors in addition to microtubules also act in controlling the secondary wall pattern, since we observe that even in the absence of microtubules secondary thickenings of two adjacent xylem elements are deposited directly opposite one another across the common primary wall.     

Distribution of vessel size,vessel density and xylem conducting efficiency within a crown of silver birch (<Emphasis Type="Italic">Betula pendula</Emphasis>)

Spatial patterns in vessel diameter, vessel density and xylem conducting efficiency within a crown were examined in closed-canopy trees of silver birch (Betula pendula). The variation in anatomical and hydraulic characteristics of branches was considered from three perspectives: vertically within a crown (lower, middle and upper crown), radially along main branches (proximal, middle and distal part), and with respect to branch orders (first-, second- and third-order branches). Hydraulically weighted mean diameter of vessels (D _h) and theoretical specific conductivity of the xylem (k _t) exhibited no vertical trend within the tree crown, whereas leaf-specific conductivity of the xylem (LSC_t) decreased acropetally. Variation in LSC_t was governed by sapwood area to leaf area ratio (Huber value) rather than by changes in xylem anatomy. The acropetal increase in soil-to-leaf conductance (G _T) within the birch canopy is attributable to longer path length within the lower-crown branches and higher hydraulic resistance of the shade leaves. D _h, k _t and LSC_t decreased, while vessel density (VD) and relative area of vessel lumina (VA) increased distally along main branches. A strong negative relationship between vessel diameter and VD implies a trade-off between hydraulic efficiency and mechanical stability of xylem. D _h and VD combined explained 85.4% of the total variation of k _t in the regression model applied to the whole data set. Xylem in fast-growing branches (primary branches) had greater area of vessel lumina per unit cross-sectional area of sapwood, resulting in a positive relationship between branch radial growth rate and k _t. D _h, k _t and LSC_t decreased, whereas VD increased with increasing branch order. This pattern promotes the hydraulic dominance of primary branches over the secondary branches and their dominance over tertiary branches. In this way crown architecture contributes to preferential water flow along the main axes, potentially providing better water supply for the branch apical bud and foliage located in the outer, better-insolated part of the crown.     

No evidence for an open vessel effect in centrifuge-based vulnerability curves of a long-vesselled liana (Vitis vinifera)

Vulnerability to cavitation curves are used to estimate xylem cavitation resistance and can be constructed using multiple techniques. It was recently suggested that a technique that relies on centrifugal force to generate negative xylem pressures may be susceptible to an open vessel artifact in long-vesselled species. Here, we used custom centrifuge rotors to measure different sample lengths of 1-yr-old stems of grapevine to examine the influence of open vessels on vulnerability curves, thus testing the hypothesized open vessel artifact. These curves were compared with a dehydration-based vulnerability curve. Although samples differed significantly in the number of open vessels, there was no difference in the vulnerability to cavitation measured on 0.14- and 0.271-m-long samples of Vitis vinifera. Dehydration and centrifuge-based curves showed a similar pattern of declining xylem-specific hydraulic conductivity (K(s)) with declining water potential. The percentage loss in hydraulic conductivity (PLC) differed between dehydration and centrifuge curves and it was determined that grapevine is susceptible to errors in estimating maximum K(s) during dehydration because of the development of vessel blockages. Our results from a long-vesselled liana do not support the open vessel artifact hypothesis.     

Development of cambium and length of vessel elements and fibers in dwarfAlnus hirsuta (Spach) rupr

In a comparison of cambial cells and their derivatives between naturally occurring dwarf and normal trees, vessel elements and fibers in the annual rings of dwarf trees were found to be shorter, narrower and fewer than those of normal trees. The frequency of anticlinal divisions and loss of cambial initials were low during the differentiation of xylem cells from cambial initials in dwarf trees. The length and intrusive growth of fusiform initials were slightly less than those of normal trees. Thus, it was concluded that the shortening of vessel elements and fibers in dwarf trees was due to the fact that cambial initials were themselves shortened and underwent inactive intrusive growth during differentiation of the xylem mother cells.     

Relationships among xylem transport, biomechanics and storage in stems and roots of nine Rhamnaceae species of the California chaparral

Here, hypotheses about stem and root xylem structure and function were assessed by analyzing xylem in nine chaparral Rhamnaceae species. Traits characterizing xylem transport efficiency and safety, mechanical strength and storage were analyzed using linear regression, principal components analysis and phylogenetic independent contrasts (PICs). Stems showed a strong, positive correlation between xylem mechanical strength (xylem density and modulus of rupture) and xylem transport safety (resistance to cavitation and estimated vessel implosion resistance), and this was supported by PICs. Like stems, greater root cavitation resistance was correlated with greater vessel implosion resistance; however, unlike stems, root cavitation resistance was not correlated with xylem density and modulus of rupture. Also different from stems, roots displayed a trade-off between xylem transport safety from cavitation and xylem transport efficiency. Both stems and roots showed a trade-off between xylem transport safety and xylem storage of water and nutrients, respectively. Stems and roots differ in xylem structural and functional relationships, associated with differences in their local environment (air vs soil) and their primary functions.     

Behind the curtain of the compartmentalization process: Exploring how xylem vessel diameter impacts vascular pathogen resistance

A key determinant of plant resistance to vascular infections lies in the ability of the host to successfully compartmentalize invaders at the xylem level. Growing evidence supports that the structural properties of the vascular system impact host vulnerability towards vascular pathogens. The aim of this study was to provide further insight into the impact of xylem vessel diameter on compartmentalization efficiency and thus vascular pathogen movement, using the interaction between Vitis and Phaeomoniella chlamydospora as a model system. We showed experimentally that an increased number of xylem vessels above 100 μm of diameter resulted in a higher mean infection level of host tissue. This benchmark was validated within and across Vitis genotypes. Although the ability of genotypes to restore vascular cambium integrity upon infection was highly variable, this trait did not correlate with their ability to impede pathogen movement at the xylem level. The distribution of infection severity of cuttings across the range of genotype's susceptibility suggests that a risk-based mechanism is involved. We used this experimental data to calibrate a mechanistic stochastic model of the pathogen spread and we provide evidence that the efficiency of the compartmentalization process within a given xylem vessel is a function of its diameter.     

银桦次生木质部导管分子观察研究

对银桦 (Grevillearobusta)次生木质部导管分子进行了观察研究。在银桦次生木质部导管分子中存在着许多不同的样式 ,分别对其进行了描述 ,并从导管分子个体发育与系统发育的角度进行了讨论。银桦导管分子中还存在着特殊的样式 ,如具三个单穿孔的导管以及导管分子侧壁上存在明显的皱褶 ,对其也分别进行了讨论     

Comparative vessel anatomy of arctic deciduous and evergreen dicots

Arctic tundra plant species exhibit striking variation in leaf character and growth form. Both are likely related to differences in vessel anatomy, and all may affect responses to climate changes in the Arctic. To investigate the relationships among leaf character, growth form, vessel anatomy, and susceptibility to freeze-thaw-induced xylem cavitation, xylem vessel characteristics were compared among six deciduous and six evergreen arctic dicot species of erect and prostrate growth forms. We hypothesized that deciduous and erect species would have larger and longer vessels than evergreen and cushion/mat-forming species. Vessel lengths, diameters, and densities were measured for each species. Theoretical vessel flow rates were calculated using Poiseuille's law for ideal capillaries. Flow rates were used to determine the susceptibility of vessels to cavitation induced by freeze-thaw events that may become more frequent with global warming. Vessel diameters were larger in deciduous species compared to evergreens, and in shrubs/trees vs. cushion/mat-forming plants. Vessel length distributions, however, did not differ for growth form or leaf character. Vessel density was greater in cushion/mat-forming species than in shrub/tree species. Deciduous plants showed a greater contribution to total conductivity by relatively larger vessels than evergreens. One of the deciduous species, Vaccinium uliginosum, is predicted to be susceptible to freeze-thaw-induced cavitation. These results have important implications for future arctic species composition and plant community structure.