稻鸭共作及其它控草措施对稻田杂草群落的影响

运用群落生态学方法研究了稻鸭共作、人工除草、化学除草3种控草措施对稻田杂草群落特征的影响及其对田间杂草的控制作用.结果表明,稻鸭共作显著降低了田间杂草的发生密度,对稻田主要杂草鸭舌草(Monochoriavaginalis)、异型莎草(Cyperusdifformis)、矮慈姑(Sagittariapygmaea)的防效均达到95%以上,总体控草效果显著优于化学除草和人工除草.稻鸭共作使稻田杂草群落的物种丰富度及Shannon-Wiener多样性指数略有降低,但Pielou均匀度指数显著提高,表明群落物种组成有了很大的改变,降低了原来优势杂草的发生危害.在不同控草措施作用下,稻田杂草群落的结构组成也发生了一定的变化,稻鸭共作区群落组成为陌上菜(Linderniaprocumbens)+异型莎草+水虱草(Fimbristylismiliacea),Whittaker群落指数显著高于化学除草、人工除草及对照区,表明稻鸭共作对田间杂草群落结构影响较大.从Sorensen群落相似性指数及以其为距离测度指标的聚类分析结果中也可得到同样的结论.     

新疆博格达山地面生苔藓植物物种多样性研究

采用相似性系数和物种多样性指数对新疆博格达山地面生苔藓植物的物种多样性进行了研究．结果表明,博格达山地区苔藓植物区系具有丰富性和复杂性的特点,共有地面生苔藓植物32科73属186种(含变种、变型);山地荒漠带和山地草原带苔藓植物物种相似性最高,为0．6809,山地森林带和高山垫状植被带相似性最低,仅为0．1342;山地森林带苔藓植物在整个博格达山地面生苔藓植物群落中占据优势地位;山地森林带苔藓植物物种多样性最为丰富,为该山地苔藓植物多样性的分布中心,是苔藓植物多样性保护的关键地区．     

利用Excel电子数据表计算遗传相似系数的方法

利用分子标记技术对生物物种群进行类群分类时,一般需要通过分析电泳图谱获得0/1矩阵,通过统计计算来得到其遗传相似系数和遗传距离指数。科学工作者常借助计算器徒手计算,容易出错,速度又慢。本文介绍一种以MicrosoftExcel电子数据表为平台,能较轻松又准确地根据0/1矩阵实现遗传相似系数和遗传距离指数计算的操作方法。     

河北省侧蒴藓类植物的地理成分及其与邻近地区的比较

通过对河北省侧蒴藓类植物较详尽的野外考察、标本采集、鉴定和系统研究,已知河北省侧蒴藓类植物17科,66属,196种(包括种下单位),其地理成分可划分为9种类型,北温带分布型占主导地位,东亚分布型次之,热带分布型不起主要作用。运用物种丰富度、优势科比较、属相似性系数等统计方法,对河北与邻近地区的区系地理成分进行了比较、分析和讨论。从河北省与我国东北、内蒙古、山东、秦岭、西藏和横断山等6个地区侧蒴藓类区系组成的比较分析得出,本省该类群物种丰富度位居第4,横断山居于第1位,河北与其它6个地区的共有优势科前3位为青藓科、柳叶藓科、灰藓科;河北与内蒙古、山东相似程度最高,与东北和秦岭相似程度次之,与西藏、横断山相差最大。同时对这7个地区的具体地理成分也作了比较。这些结果有力地说明了河北省侧蒴藓类植物区系具有明显的温带性质,同时兼有浓厚的东亚区系色彩,也表明了中国华北与日本、欧洲和北美东北部在苔藓植物区系物种起源上有深厚的历史渊源。     

The Role of the Fast Motion of the Spin Label in the Interpretation of EPR Spectra for Spin-Labeled Macromolecules

Abstract

The spin label method was used to observe the nature of the fast motions of side chains in protein monocrystals. The EPR spectra of spin-labeled lysozyme monocrystals (with different orientations of the tetragonal protein crystal in relation to the direction of the magnetic field) were interpreted using the method of molecular dynamics (MD). Within the proposed simple model, MD calculations of the spin label motion trajectories are performed in a reasonable real time. The model regards the protein molecule as frozen as a whole and the spin labeled amino acid residue as unfrozen. To calculate the trajectories in vacuum, a model of spin-labeled lysozyme was assembled, and the parameters of the force fields were specified for atoms of the protein molecule, including the spin label. The calculations show that the protein environment sterically limits the area of the possible angular reorientations for the NO reporter group of the nitroxide (within the spin label), and this, in turn, affects the shape of the EPR spectrum. However, it turned out that the spread in the positions of the reporter group in the angle space strictly adheres to the Gaussian distribution. Using the coordinates of the spin label atoms obtained by the MD method within a selected time range and considering the distribution of the spin label states over the ensemble of spin-labeled macro- molecules in a crystal, the EPR spectra of spin-labeled lysozyme monocrystals were simulated. The resultant theoretical EPR spectra appeared to be similar to experimental ones.     

Similarity Study on Peptide ?-turn Conformation Mimetics

The ability of a series of structures to mimic the geometric and electronic properties of an ideal –turn has been studied. Initially, an exhaustive conformational analysis was carried out using the molecular dynamics technique at high temperature followed by minimization. Additionally, each minimum was optimized with the semi–ab initio molecular orbital method SAM1. Then, the unique minima found have been superimposed with ideal –turns, classic and inverse, using the SEAL program which takes into account steric and electronic parameters for the superpositions and finally, three molecular similarity indices were determined for each superposition. These indices consider the general steric and electronic characteristics of the structures, as well as, the position of the carbon atoms that correspond to the Cⁱ and Cⁱ⁺² in the peptide chain.     

Species turnover and diversity patterns along an evergreen broad-leaved forest coenocline

Direct gradient analysis was applied to the evergreen broad-leaved forest coenocline in the Tatera Forest Reserve, Japan. 10 quadrats of 0.1 -0.05 ha were laid out from 140 m to 560 m above sea level at intervals of 25–70 m. Gradient analysis revealed that distributions of many species terminated or started at ca. 400 m. Community similarity, calculated in Percentage Similarity (PS) and Community Coefficient (CC), changed abruptly below and above the 400 m contour, suggesting a change of vegetation structure at this altitude, which was also clear from population distributions. The spatial turnover rate of species along the altitudinal gradient was calculated in two ways: as the Average turnover rate along the whole range of the gradient, and as the Zone turnover rate at individual altitudes. The overall rates calculated for five categories of populations: DBH > 10 cm, DBH >3 cm, all woody species, herb-layer, and total vegetation, were- 0.0011 to- 0.0021 for PS, and - 0.0009 to- 0.0019 for CC. The calculated rates (PS basis) indicate that a 95% change in species composition is reached at 1120 to 620 m altitude. Similarly, the rates -0.0009 to - 0.0019 (CC) correspond to 1410 - 680 m. The altitudinal range expected here for a 95% change agrees with the actual elevation of forest zonation in northwestern Kyushu. The average rate of both PS and CC in the herb-layer population was 1.56 times higher than the rate in the woody species population, showing a more rapid change in herb-layer population than in the woody ones along the gradient. The Zone turnover rates were higher at the 370–440 m belt than those below and above the belt. This coincided with the interchanging pattern in population distributions and the abrupt change in similarity at about 400 m above sea level. This may be due to the change in environmental conditions such as physiography and air humidity. In the diversity measurements, the species density per 100 m² showed a gradual increase in the DBH >3 cm population but a constant level in the DBH >10 cm population along the whole range of the forest coenocline studied, while index values of S₍₁₀₀₎ and Shannon's H showed decreasing trends in the same gradient with a few exceptionally high and low values.     

A new approach to the minimal area of a plant community

Current methods for the determination of the minimal area of a phytocoenosis are compared. A new method is described. It is based on the increase in average quantitative similarity between plots in series of nested plots of increasing size in relation to species richness anddominance relations. A simulation model composed of coenotic molecules sensu Moravec is developed from which these relations can be deduced. Both a quantitative and a qualitative minimal area are derived in this way. The analytical minimal area is then defined in relation to the largest of the two minimal area values, because in this way both the species richness and the dominance relations will be represented.Some examples of grasslands and heathlands are presented. Some further investigations are suggested to improve the approach and to link it with pattern and dominance-diversity studies.Nomenclature of plant species follows Heukels-van Ooststroom (1977), of syntaxa Westhoff & den Held (1969) and de Smidt (1975)We thank Dr. Jaroslav Moravec, Pruhonice, for discussions, Drs. Onno van Tongeren, Nijmegen for help with calculations and Cyril Liebrand and Leo Mertens, Nijmegen for help with salt marsh analyses and discussions on dominance-diversity relations.Research was carried out when the authors were at the Division of Geobotany, University of Nijmegen.     

Finite-state models in the alignment of macromolecules

Summary Minimum message length encoding is a technique of inductive inference with theoretical and practical advantages. It allows the posterior odds-ratio of two theories or hypotheses to be calculated. Here it is applied to problems of aligning or relating two strings, in particular two biological macromolecules. We compare the r-theory, that the strings are related, with the null-theory, that they are not related. If they are related, the probabilities of the various alignments can be calculated. This is done for one-, three-, and five-state models of relation or mutation. These correspond to linear and piecewise linear cost functions on runs of insertions and deletions. We describe how to estimate parameters of a model. The validity of a model is itself an hypothesis and can be objectively tested. This is done on real DNA strings and on artificial data. The tests on artificial data indicate limits on what can be inferred in various situations. The tests on real DNA support either the three- or five-state models over the one-state model. Finally, a fast, approximate minimum message length string comparison algorithm is described.Offprint requests to: L. Allison     

Graph theoretical methods for comparing phytosociological structures

This paper describes some methods that can be used to compare the phytosociological structure of plant communities using some graph theoretic properties of the directed graphs that represent them. In such a graph, the species are represented by points and the association of species A with species B is represented by a directed line segment going from B to A. Two communities can be compared using simple indices to measure the similarity of their species-lists (point similarity) and of the species associations in them (line similarity). A more sophisticated and informative measure of line similarity is the probability that, given the number of points shared by two graphs, they have at least as many lines in common as they are observed to have. A formula for calculating that probability is given here. The graphs of community structure can also be compared with respect to the homogeneity of the distribution of the lines among the points, a property related to the number of species that are important in determining the composition of the community. These techniques are illustrated using the graphs of the phytosociological structure of intertidal seaweed communities on the southeast coast of Nova Scotia.Nomenclature follows: South and Cardinal (1970)