Isozyme variation in tropical trees: patterns of genetic organization

Tropical forests have long been of interest to biologists because of their high species diversity and their complicated patterns of community organization. The traditional notion of the rain forest as an ancient, unvarying archive of species has been challenged by a host of recent ecological studies which have demonstrated that tropical trees are diverse in their reproductive biology and dynamic in their population structure.Data from 97 isozyme studies on the genetics of tropical woody species demonstrate that cultivated taxa maintain higher percentages of polymorphic loci and higher mean heterozygosities than native tropical species. Levels of within-population variation in tropical taxa are as high or higher than in plants in general, previously reviewed by Hamrick and Godt (1989). Levels of genetic variation differ significantly among species with different geographic ranges, life forms, and taxonomic affinities. Levels of population differentiation, measured by Gs, values, are significantly different only between species with different seed dispersal modes. Outcrossing rates in 16 tropical tree species showed a preponderance of highly outcrossed breeding systems. Genetic evidence suggests that gene flow among local populations is high, but geographically separated populations show moderate levels of genetic differentiation.Ecological and historical processes provide the mechanisms influencing the genetic architecture of plant species. Where appropriate, data on isozyme variation in tropical trees are related to breeding systems, seed dispersal mechanisms, demography, and patterns of environmental heterogeneity. Profitable avenues for future research are suggested.     

Gene dispersal within forest tree populations

Patterns of gene dispersal by seeds and pollen greatly influence the genetic structure of plant populations and their effective size. This paper reviews methods of measuring gene dispersal and current information on patterns of dispersal within local populations of forest trees. Recently, a number of statistical procedures for investigating gene movement based on the use of large numbers of isozyme loci have been described. These procedures include various forms of parentage analysis and the fitting of mating models to genotypic arrays of offspring from individual maternal plants. With the levels of genetic discrimination currently possible in forest trees, the model approach appears to be the most reliable means of estimating gene dispersal parameters. Too little data are available to draw general conclusions about patterns of gene movement within natural populations. Nevertheless, reports to date indicate that dispersal by both pollen and seed can be considerable. For any one mother tree, the bulk of effective pollen in conifers may come from distant males in the same stand or from surrounding stands (gene flow). In insect-pollinated angiosperms, gene flow may also be substantial, but cross-fertilization within stands may primarily be between nearest flowering trees.     

Anthropogenic alterations of genetic diversity within tree populations: Implications for forest ecosystem resilience

Healthy forests provide many of the essential ecosystem services upon which all life depends. Genetic diversity is an essential component of long-term forest health because it provides a basis for adaptation and resilience to environmental stress and change. In addition to natural processes, numerous anthropogenic factors deplete forest genetic resources. Genetic losses could be particularly consequential now because robust resilience is needed to respond to a growing number, variety, and frequency of stress exposures. Silvicultural management that selectively removes trees (and their genes) from forests may be another force reshaping forest gene pools. Although data concerning the influence of silvicultural management on genetic resources in temperate forests is somewhat mixed, through the genetic assessment of long-term silvicultural treatments within an eastern hemlock (Tsuga canadensis) forest, and computer-based simulated harvests of a genetically mapped eastern white pine (Pinus strobus) stand, we found that the selective removal of trees can alter gene frequencies. Due to an association with phenotypic characteristics used to guide harvests, the frequencies of rare alleles appeared particularly vulnerable to manipulation. Depending on the selection criteria used, rare allele frequencies either remained steady, decreased, or increased relative to study controls. Although harvest-associated genetic losses are possible, our data suggests that management can also sustain or enhance genetic richness. Similar to studies within temperate ecosystems, recent research in tropical forests underscores the potential influence of harvesting on the genetics of tree populations. In addition to efforts to reduce controllable sources of ecosystem stress (e.g., high pollutant exposures), management options should be evaluated that may bolster forest ecosystem resilience by preserving levels of genetic diversity within forests.     

Factors shaping genetic structure within populations ofEurya japonica (Theaceae)

Starch-gel electrophoresis was used to resolve nine polymorphic enzyme loci from leaf tissue collected from 20 Korean populations ofEurya japonica in order to determine differences in allele frequencies between male and female trees. In addition, 84 adults were sampled and mapped in a population located on Naenaro Island in Korea to examine spatial genetic structure using spatial autocorrelation analysis. Allele frequencies between males and females gave few contribution to the genetic structuring within populations. Only nine (5%) of 180 cases were significantly different from both sexes in allele frequencies. On the other hand, Moran'sI was significantly different from the expected value in 31 (23.5%) of 132 cases. In the shortest distance (0<5m),I was significantly positive in 10 (22.7%) of 44 cases. The results indicate that a significant small scale genetic structure was detected in the population and patch widths were inferred to be approximately 5–7 m. A nonrandom distribution of genotypes may be indicative of restricted gene flowvia seed and pollen dispersal, and patchy establishments of genetically distinct individuals. These factors are responsible for shaping population genetic structure ofE. japonica.     

广西火桐自然种群和迁地保护种群的遗传多样性比较

采用ISSR标记方法,对广西火桐Erythropsis kwangsiensis 10个自然种群和1个迁地保护种群的遗传多样性和遗传结构进行了分析和比较。结果表明:用10个引物从广西火桐总DNA中共扩增出60条带,其中多态性条带51条。自然种群中以维新种群的遗传多样性最高,而三叠岭瀑布种群最低。自然种群的总遗传变异Ht为0.281 5,种群内遗传变异HS为0.076 4,种群间遗传变异为0.205 1,基因流为0.183 2。迁地保护种群的HEt和HES均为0.118 8。自然种群间存在一定程度的遗传分化(Gst=0.731 9),种群间变异占主导地位。合并后的自然种群的多态性条带百分率(RPPB)、Nei’s多样性指数(H)和Shannon信息指数(I)均高于迁地保护种群,分别为85.00%和31.67%、0.284 1和0.118 8、0.428 5和0.175 7。研究结果表明:广西火桐迁地保护种群的遗传多样性较低,未能涵盖整个种群。建议从多个自然种群中收集种子,尽可能多的采集样本,分区育苗种植,以增加遗传多样性水平。     

Control of the first flowering in forest trees 1

Precocious flowering provides opportunities to shorten a breeding cycle. A tree may flower for the first time when sufficient crown development has occurred and there are enough meristems to support both vegetative and reproductive buds. Precocious flowering can be promoted through the use of cultural techniques, such as photoperiod, accelerated growth, gibberellins and water stress. The length of the juvenile phase is dependent on genetic and environmental variables that affect achievement of a minimum size, and is positively correlated with the height of the plants within a family. Selection pressure can be applied successfully to the precocious flowering character, and crossed or inbred lines of precocious flowering progeny can be developed. Various levels and amounts of genetic control have been implicated in the control of precocious flowering.     

Genetic structure of populations of beech (Fagus sylvatica L.) in Denmark

The genetic structure in Danish indigenous and introduced provenances of beech (Fagus sylvatica L.) is described. Ten stands are analysed based on variation revealed by seven enzyme systems. The present study reveals significant allele frequency differences between populations with a small absolute amount of genetic differentiation, with no pattern related to geographic distance. The genetic differentiation between indigenous populations measured by Wright's F _ST‐statistic does not deviate significantly from zero, and only 2.9% of the total genetic variation in the foreign populations was due to interpopulation differences, The allele frequencies in relatively small and isolated populations do not differ from the frequencies found in larger areas with beech forest. The low genetic differentiation of isozyme level between indigenous and foreign populations was opposed by significant differences in foliation performance measured on three pairs of neighbouring stands. Foliation performance in adjacent stands of indigenous and introduced beech indicates that quantitative characteristics must be considered separately from neutral variation at single loci.     

林木遗传图谱的构建策略及存在的问题

遗传图谱是开展数量性状基因定位、标记辅助育种以及基因克隆等研究的基础,在理论和育种实践上都具有重要的意义,本文较为详尽地阐述了林木遗传图谱的构建过程,针对林木的自身特点探讨林木遗传图谱的作图策略,同时指出当前林木遗传图谱构建中存在的问题,并对林木高质量遗传图谱构建提出展望。     

Patterns of variation in chemical compositions of wood from natural populations of Pinus manssoniana Lamb. in Guizhou Province, China

Patterns of variation in the chemical composition of wood,i.e.,holocellulose,cellulose and lignin contents and 1%NaOH extractives were studied in 12 natural populations of Pinus manssoniana Lamb.in Guizhou Province,China,using wood cores as experiment material.The results show statistically significant differences among provenances in holocellulose,cellulose and 1% NaOH extractive contents.The largest coefficient of variation among the provenances was found in the 1%NaOH extractive content and the smallest in the holocellulose content.Variation of lignin content occurred within provenances.Correlations between chemical compositions of wood and factors of local geography and meteorology were largely insignificant.The chemical composition of wood presented patterns of random variation.The correlation of 1%NaOH extractive content with holocellulose content was significant(r=?0.68).There was also significantly negative correlation(r=0.62)between cellulose and lignin content.On the basis of a UPGMA cluster analysis,we identified three provenances of masson pine among the 12 studied,i.e.,those of Wengan,Tongzi and Luodian with high cellulose contents,low levels of 1%NaOH extractive and moderate lignin contents,which we recommend as promising provenances for growing of pulp wood and the manufacture of paper in Guizhou Province     

南雄青嶂山常绿阔叶林优势物种组成与结构分析

基于1 hm2的固定样地数据,对粤北南雄小流坑—青嶂山保护区亚热带常绿阔叶林的物种多样性及优势植物种群的年龄、高度结构等特征进行了分析,以探讨森林群落的稳定性与演替进程.结果表明,样地中出现胸径≥1.0 cm的植物38科58属74种,个体总数1621株,建群种为木荷(Schima su-perba)和红锥(Castanopsis hystrix),重要值分别为16.56和12.00;优势种为赤皮青冈(Cyclobalanopsis gilva)、黄樟(Cinnamomum porrectum)、华润楠(Machilus chinensis)、青冈(Cyclobalanopsis glauca);群落优势科为山茶科、壳斗科、樟科、茜草科;群落整体上处于稳定阶段,其中木荷和青冈为稳定至早衰种群,红锥和赤皮青冈为基本稳定种群,华润楠为稳定种群,黄樟为衰老种群;各植物种群高度结构各具特色,其中木荷、华润楠和青冈对整个群落的高度结构影响较大.     

Spatial and microgeographical genetic differentiation of black alder (Alnus glutinosa Gaertn.) populations

Three Alnus glutinosa populations from central Slovakia were investigated by means of isozyme analysis. The average expected heterozygosity ranged from 0.151 to 0.173. Despite significant differences in allele frequencies among populations, genetic differentiation was low (F_ST=0.022). Intrapopulation fixation indices indicate no or very slight deviation from panmictic expectations towards the heterozygote deficiency. No indications were found that the investigated populations have experienced recent bottlenecks in population size. A spatial autocorrelation analysis based on Moran’s I indicates the existence of a spatial genetic structuring in the population Král’ová. Patch size was estimated to be 70–100 m, which is more than observed in other broadleaved tree species. This difference is explained by the linear shape of alder populations and a higher mobility of seeds.     

林业苗圃杂草种群结构的研究

林业苗圃杂草种群结构的研究结果表明:苗圃地的杂草种群结构受环境条件的影响,不同的覆盖物、不同的时期杂草种群的结构有所差异;苗圃杂草种群的形成有一定的规律,遵循S型曲线的变化规律;杂草种群个体数量的高发生期在10 d左右,一般在6月中旬大量发生;播下林木种子后,立即施用除草剂,能够有效地控制杂草种群,缩短杂草的大量发生期限。     

Genetic variation ofAlnus trabeculosa populations in Japan

Alnus trabeculosa Hand.-Mazz. is classed as “near threatened,” and efforts should be made to conserve the species, but effective action would require understanding of its genetic variation and structure. Therefore, the genetic variation at 12 isozyme loci was examined in seven populations of the species in Japan. The expected heterozygosity within species (H _es=0.222) and the expected heterozygosity within populations (H _ep=0.199) were found to be slightly higher than in most other woody species. The coefficient of genetic differentiation (G _ST=0.146) was also high. The northernmost population had the lowest values for almost all measures of genetic variation, and populations in southern Japan tended to show greater within-population variation than those in northern Japan. The level and distribution of genetic variation in this species might be related to its life history and ecological traits, and distribution history.     

石栎、青冈栎和杉木混交林分的空间结构

为了弄清优质林分的结构特征,应用传统林分结构因子分析方法,配合混交度、角尺度、大小比数3个林分空间结构参数,分析了位于江苏宜兴近郊的自然保护区内宜兴小黑沟石栎、青冈栎、杉木混交林的空间结构特征。结果表明:石栎、青冈栎、杉木混交林物种丰富度较高,乔木层共出现9个树种,径级结构分布连续,群落垂直结构特征明显,可分为3个林层;林分平均混交度为0.516,处于强度混交状态;林分平均角尺度为0.482,属于随机分布;林分平均大小比数为0.482,有超过40%的林木处于优势状态;石栎、青冈栎和杉木种群优势度明显,群落暂时处于相对稳定状态。     

Cortical monoterpene variation in natural populations of Pinus sylvestris in Sweden

Cortical oleoresins were obtained from 10 natural populations of Pinus sylvestris L. from different geographical localities. Gas chromatography was used to determine quantities of individual monoterpenes. Considerable variation was found in monoterpene composition among different populations. High proportions of limonene occurred in greater percentages in trees of northern origins, while high sabinene was frequently found in southern trees. Mean proportions of limonene and sabinene in the populations were clinal with latitude. For some monoterpenes, variation coefficients as a measure of variability within populations appeared to be clinal with latitude. 85.4% of the variance in monoterpene composition was found within populations and 14.6 between populations. Discriminant analysis differentiates populations from different geographical localities into different groups. The differences in monoterpene patterns between adjacent populations were statistically nonsignificant. It is recommended that monoterpene composition be used for more general study of genetic variation, geographical distinction between different populations and seed certification purposes.     

天山樱桃野生居群遗传多样性SSR分析

为给天山樱桃种质资源的保护和开发利用提供参考,应用SSR标记技术对新疆天山樱桃4个居群44份种质的遗传多样性进行分析。结果表明:筛选的14对SSR引物共检测到191个位点,包含148个多态性位点。Nei’s基因多样性指数和Shannon信息指数分别为0.239 8和0.367 6,各居群遗传分化系数为0.193 5,基因流为2.084 3。天山樱桃遗传分化水平较低,各居群间基因交流频繁,遗传变异主要存在于居群内。由基于遗传距离的聚类结果可知,裕民县与大西沟居群遗传关系最近,与特克斯居群遗传距离较远,4个天山樱桃居群中大西沟居群遗传多样性最高。     

Genetic diversity of natural Hepatacodium miconioides populations in Zhejiang Province

Hepatacodium miconioides is the Class II protected plant species in China. This paper studies the genetic diversity and differentiation of its nine natural populations in Zhejiang Province by using random amplified polymorphic DNA (RAPD) technique. Twelve random primers were selected in the amplification, and 164 repetitive loci were produced. The percentage of polymorphic loci in each H. miconioides population ranged from 14.60% to 27.44%, with an average of 20.73%. Among the test populations, Kuochangshan had the highest percentage of polymorphic loci, Simingshan took the second place, and Guanyinping had the lowest percentage. As estimated by Shannon index, the genetic diversity within H. miconioides populations accounted for 27.28% of the total genetic diversity, while that among H. miconioides populations accounted for 72.72%. The genetic differentiation among H. miconioides populations as estimated by Nei index was 0.715,7. This figure was generally consistent with that estimated by Shannon index, i.e., the genetic differentiation among populations was relatively high, but that within populations was relatively low. The gene flow among H. miconioides populations was relatively low (0.198,7), and the genetic similarity ranged from 0.655,7 to 0.811,9, with an average of 0.730,6. The highest genetic distance among populations was 0.422,9, while the lowest was 0.208,3. All the results showed that there was a distinct genetic differentiation among H. miconioides populations. The genetic distance matrix of nine test populations was calculated using this method, and the clustering analysis was made using the unweighted pair group method with arithmetic mean (UPGMA). The cluster analysis suggested that the nine populations of H. miconioides in Zhejiang Province could be divided into two groups, the eastern Zhejiang group and the western Zhejiang group. __________ Translated from Chinese Journal of Applied Ecology, 2005, 16(5): 795–800 [译自: 应用生态学报, 2005, 16(5): 795–800]     

Spatial structure of deciduous forest stands with contrasting human influence in northwest Spain

Five contrasting deciduous forest stands were studied to characterize the spatial structural variability in human-influenced forests. These stands are representative of cultural forest types widely represented in western Europe: one plantation, two coppices, one wood-pasture forest and one high forest stand. All stems with DBH > 5 cm were measured and mapped, and stem DBH distributions, spatial structure of DBH, spatial point patterns and spatial associations were analysed. Spatial autocorrelation for DBH was calculated with Moran’s I correlograms and semivariograms. Complete spatial randomness hypothesis for spatial point patterns, and both independence and random labelling hypotheses for spatial associations were analysed using Ripley’s K function. The results showed that tree sizes were conditioned by particular former management systems, which determined unimodal symmetric, positively skewed or compound DBH distributions. Spatial structure was more complex when human influence became reduced. Coppice stands showed clumped spatial patterns and independence among size classes, as a consequence of sexual and vegetative establishment of new stems in open areas. The largest clumping intensity was observed in the wood-pasture with an intermediate disturbance frequency and low inter-tree competition. The high forest stand displayed spatial traits consistent with the gap-dynamics paradigm, such as clumping of smaller trees, random arrangement of larger trees, negative association between juveniles and adults, and high structural heterogeneity. It can be expected that after cessation of human interference, coppices and wood-pastures would evolve to a more heterogeneous structure, probably with a higher habitat and species diversity.     

利用根癌农杆菌转化木本植物的研究进展

本文着重论述了近年来国内外利用根癌农杆菌介导法转化林木的研究进展。简述了获得转基因林木的应用现状,并将国内外林木转基因工作给以概括,提出了转化过程中存在的问题,并对这一转化方法的应用前景进行了展望。     

木兰围场天然次生油松林年龄结构及更新动态研究

通过对天然次生油松林下更新状况的调查,编制静态生命表、绘制存活曲线,研究分析河北木兰围场自然保护区内不同立地条件(坡底、坡中、坡顶)下天然油松次生林的年龄结构和更新动态,结果表明:(1)影响天然次生油松林更新的主要因子是郁闭度、灌草盖度。较高郁闭度、较高湿度更利于油松更新,幼苗更新密度最大值达4.192株/m2。(2)该保护区不同立地条件下油松种群年龄结构均为增长型年龄锥体;0~10a生个体数最多,坡中处最多达525株;生命期望最大值集中于10~20a龄级,该龄级属于生理旺盛期,应予以保护。(3)不同立地条件下油松种群的存活曲线变化趋势相似,油松存活率均在10~20a生间急剧下降;在20~60a生间,除坡底30~60a生存活曲线逐渐下降外,坡中和坡顶的存活曲线均大体趋于稳定,但60a生后3块标准地存活曲线均大幅下降,其中坡底处油松种群在70a存活率最小,为0;整体而言,存活率由大到小依次为坡顶、坡底、坡中。