瑞士阿尔卑斯山欧洲落叶松居群的遗传变异和分化

应用等位酶分析技术,沿两个海拔梯度在瑞士阿尔卑斯山研究了欧洲落叶松（Larix decidua Mill.)居群内和居群间的遗传多态性,结果表明,多态性位点的比例为22.9%,平均每个位点的等位基因数为1.3,平均期望杂合度为0.095,遗传变异的5.8%存在于居群之间,平均遗传距离为0.006。几个有统计意义的基因频率差别在不同树龄类被发现,正在繁育系数值表明在瑞士阿尔卑斯山欧洲落叶松居群有相当的杂合体缺乏,在阿尔拜特（Ar-pette),海拔最高的亚居群与其他亚居群相比较显示最低的遗传多态性（如显示最低的我态性位点比例和最低的平均期望杂合度）和最大的遗传距离值,在最高亚居群和其他亚居群间的遗传差别暗示奠基效应可能是影响这个定样场所欧洲落叶松居群遗传分化的主要因素。     

杭州午潮山天然次生林木本幼苗组成及其时空分布格局

木本植物幼苗是森林生态系统的重要的组成部分,其定居、存活、生长的生态学过程对于森林植被的更新具有潜在指示和筛选作用。为探究浙江杭州午潮山亚热带常绿阔叶次生林群落更新和演替机制,基于样方法对150 m²样地内天然更新幼苗的物种组成、数量特征和基径结构进行统计,在此基础上采用最近邻分析和Ripley''s K函数的点格局方法,分析其中主要优势树种的更新动态及其时空分布格局。结果表明:(1)样地内乔木幼苗树种组成丰富,共调查到幼苗811株,隶属12科20属27种,其中樟科Lauraceae、壳斗科Fagaceae、山茶科Theaceae和山矾科Symplocaceae为主要优势科。(2)红楠Machilus thunbergii、薄叶润楠M. leptophylla、毛柄连蕊茶Camellia fraterna和刨花润楠M. spauhoi在所有调查物种重要值排序前4,因而被确定为优势林下植物,绘制的基径结构小提琴图(violin plot)进一步显示它们的种群分属快速增长型、稳定增长型、缓慢增长型和稳定型。(3)红楠、薄叶润楠和刨花润楠在小径级和小尺度上多呈聚集分布,随生长发育和空间尺度的增加,聚集强度呈现先增高后降低趋势,最终向离散分布或随机分布转变,可视为群落演替的早期树种;同时,三者在聚集强度上有所差异,排序为红楠＞薄叶润楠＞刨花润楠。毛柄连蕊茶Camellia fraterna种群密度较低,在小径级和小尺度上呈随机分布,随生长发育和空间尺度的增加,聚集强度呈波动趋势,最终向离散分布转变,可视为演替的中期树种。本研究在小尺度上初步揭了午潮山木本幼苗种群的演替过程中的种群结构和分布格局,可以为亚热带森林管理与植被恢复提供理论依据。     

模拟氮沉降对中亚热带杉木幼树根系生物量的影响

植物根系是全球陆地生态系统碳储量的重要组成部分,在全球生态系统碳循环中起着重要作用,日益加剧的氮沉降会影响根系生物量在空间和不同径级的分配,进而影响森林生态系统的生产力和土壤养分循环。以杉木幼树为研究对象,通过野外氮沉降模拟实验,研究氮沉降四年后对不同土层、不同径级根系生物量的影响。结果发现：（1）低氮和高氮处理总细根生物量较对照均无显著差异（P > 0.05）,高氮处理粗根生物量及总根系生物量较对照分别增加45%和40%（P < 0.05）;（2）与对照相比,施氮处理显著增加20-40 cm与40-60 cm土层细根和粗根生物量,且在低氮处理下,20-40 cm土层细根、粗根在总土层细根与粗根生物量的占比显著提高。（3）与对照相比,高氮处理显著增加了2-5 mm、5-10 mm及10-20 mm径级的根系生物量,低氮处理显著增加2-5 mm、5-10 mm径级根系生物量,且显著降低20-50 mm径级根系生物量。综上所述表明：氮沉降后杉木幼树通过增加较粗径级根系来增加对养分及水分的输送,同时通过增加深层根系生物量及其比例的策略来维持杉木幼树的快速生长;而根系生物量的增加,在一定程度上会增加根系碳源的输入,影响土壤碳循环过程。     

小兴安岭谷地云冷杉林粗木质残体碳密度特征

以小兴安岭谷地云冷杉林9.12 hm~2固定样地为研究对象,分析粗木质残体(CWD)碳密度的基础特征,揭示其与林分因子和物种多样性的关系。结果表明:(1)谷地云冷杉林CWD碳密度为13.25 t C/hm~2,其中云杉(Picea spp.)、冷杉(Abies nephrolepis)、兴安落叶松(Larix gmelinii)和未知种的CWD碳密度分别为3.59、2.61、3.06和2.85 t C/hm~2。(2)不同腐烂等级下CWD碳密度呈近正态分布,多集中在Ⅱ和Ⅲ等级,分别占总量的42.7%和35.4%。不同径级的CWD碳密度也呈近正态分布,主要分布在30—40 cm和40—50 cm径级上。干中折断、拔根倒、枯立木和干基折断为谷地云冷杉林CWD碳密度的主要存在方式。腐烂等级为Ⅰ和Ⅴ的CWD中,拔根倒的碳密度最高,其他腐烂等级中均为干中折断的碳密度最高。(3)CWD碳密度表现出较强的空间异质性,其随着林分平均胸径、最大胸径和胸高断面积的增加而下降,呈显著负相关关系(P0.05);而与林分密度、多样性指数和均匀度指数均无显著相关性(P0.05)。     

The energy–water limitation threshold explains divergent drought responses in tree growth,needle length,and stable isotope ratios

Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Although growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds co-occurred with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1398 needle length records, and 1075 stable isotope samples from 27 sites across whitebark pine's (Pinus albicaulis Engelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4°C (7.12–9.51°C; estimated using fall-spring maximum temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios, that emerged during drought. These co-occurring thresholds reflected the transition between energy- and water-limited tree growth (i.e., the E–W limitation threshold). This transition likely mediated carbon and nutrient cycling, as well as important differences in growth-defense trade-offs and drought adaptations. Furthermore, whitebark pine growing in energy-limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, may be offset by growth declines in water-limited regions, threatening the long-term sustainability of the recently listed whitebark pine species in the Sierra Nevada.     

The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations

Seed dispersal mechanisms should have a direct impact on the genetic structure of populations. Species whose seeds are dispersed near the maternal plant (e.g. gravity or wind dispersal) or species whose seeds are deposited in clumps or patches should have more fine-scale genetic structure than species whose seeds are dispersed singly by mobile animals. Furthermore, due to the overlap of seed shadows, species with high adult densities should have less genetic structure than species with lower densities. Allozyme analyses of three tropical tree species belonging to the moist tropical forest of Barro Colorado Island, Republic of Panama, were used to describe variation in the scale and intensity of genetic structure within their populations. The genetic structure of seedlings and immature trees in the low-density, wind-dispersed species (Platypodium elegans) was the coarsest and strongest whereas genetic structure in a population of Swartzia simplex var. ochnacea (high density, bird-dispersed) was both the finest and the weakest. The genetic structure of Alseis blackiana, a high-density, wind-dispersed species was intermediate in both degree and scale. In P. elegans and A. blackiana, which had J shaped size distributions, the significant genetic structure seen in the smaller and intermediate diameter classes disappeared in the largest diameter class. The loss of genetic structure was not observed in S. simplex, a species with a more even size distribution.     

Influence of temperature and size of females on the timing of spawning of perch,Perca fluviatilis,in Lake Geneva from 1984 to 1993

Synopsis The influence of temperature and the size of reproducing females on the timing of spawning of perch in Lake Geneva has been studied for 10 consecutive years (1984–1993) by means of artificial spawning substrates. The clutch of perch is an egg ribbon with a width proportional to the size of the reproducing female, so that the size structure distribution of the female population can be estimated from measurements of the width of the egg ribbons. The survey of egg-ribbon size revealed a succession of 3 cycles (period of increasing mean size followed by a sharp decrease) lasting 3, 3 and 4 years which were due to the occurrence of 3 strong year classes born in 1982, 1985 and 1988 respectively. This phenomenon can be explained by the effect of intraspecific predation exerted by strong year classes on the offspring of the 2 following years rather than by fluctuations in the success of reproduction in relation to climatic changes. In Lake Geneva, perch spawn in May. The water temperature exerted only a minor influence on the date of the beginning of the spawning period but had a greater effect on its intensity. A rise in temperature in May stimulated spawning while bad weather decreased spawning intensity. The larger perch had a tendency to spawn later than the small ones. The date of the mid-spawning period was well correlated with the yearly mean width of perch egg ribbons but no correlation could be detected between it and the water temperature.     

Evaluation of parents and selection for heat tolerance in the early generations of a potato (Solanum tuberosum L.) breeding program

Summary Potato cultivars (Solanum tuberosum L.) were evaluated for their capacity to form tubers under high temperature conditions (heat tolerance). In an experiment conducted in the hot summer season in the field and in experiments conducted under controlled environments in glasshouses, differences in tolerance to heat were noted among the various genotypes. Although heat tolerance tended to be associated with earliness in maturation, differences in the response to high temperatures were observed in genotypes of the same maturity class. Progeny of the cultivars Desiree and Cara, and hybrid progeny of Cara x Desiree and of Blanka x Cara were screened for heat tolerance in controlled environments in glasshouses. Long photoperiod delayed tuberization but high temperatures strongly inhibited tuber formation, which was 4% in the progeny of Desiree, <2% in the progeny of Cara and of Cara x Desiree, and ca. 16% in progeny of Blanka x Cara. For seedlings that did not form tubers in the hot glasshouse but were subsequently transferred to the cool glasshouse, tuberization was much enhanced and clones selected through this dual procedure exhibited tolerance to heat in the first conal year. The results of this study indicate that: (a) tolerance to heat is associated with earliness; however, differences in the response to heat exist among late-maturing cultivars; (b) tolerance to heat, as assessed by the capacity to form tubers under high temperatures, is genetically controlled, and the timing of tuberization might be independent of the rate of tuberization in hybrid progeny; (c) the incidence of heat tolerance in progeny population is correlated with the relative tolerance of the parents; and (d) the dual selection procedure is an efficient approach for the selection of heat-tolerant clones.     

Genetic variability of proteins from mitochondria and mitochondrial fractions of mouse organs

Proteins of whole mitochondria from mouse liver and brain and proteins of liver mitochondrial fractions (plasma and rough membrane fraction) were separated by two-dimensional electrophoresis. Protein patterns of two inbred strains of mouse, C57BL/6J and DBA/2J, and of F₁ mice of these two strains were studied. The protein patterns obtained from the different mitochondrial materials were analyzed with regard to their protein composition and the genetic variability of proteins (qualitative and quantitative protein variants). Included in this analysis are data previously obtained from the cytosols and plasma membranes of the same organs and mouse strains. The results showed the following. (1) Mitochondria and organelle-free cell components (cytosol and plasma membranes) have only a few percent of their proteins in common, while two organs, liver and brain, reveal up to approximately 50% organ-nonspecific proteins. The frequency of proteins common to solubilized and structure-bound proteins ranges below 20%. (2) Genetic variability in protein amount occurs much more frequently than genetic variability in protein structure. Liver proteins reveal more genetic variants than brain proteins. Proteins solubilized in the cell show more genetic variation than structure-bound proteins. Furthermore, the results show that with regard to the composition and the genetic variability of proteins, liver and brain differ more in their mitochondria than in their cytosol and plasma membranes.This work was supported by grants from the Deutsche Forschungsgemeinschaft awarded to Sonderforschungsbereich 29.     

River channelization effects on fish population structure in the Larraun river (Northern Spain)

As a consequence of the construction of the A-15 highway between 1991 and 1995, some modifications affecting the Larraun River (Navarra, North of Spain) were made. One of the most important effects was the channelization of a section of the river in the middle zone. Fish were caught by electrofishing in August of 1996 in the channelized reach, as well as in non-modified stretches upstream and downstream. Physical and chemical variables and shelter availability were also analyzed. The captured fish were measured (total length) and released into the river. We calculated the density, biomass, length distribution and diversity, comparing the obtained results from the different stretches. The number of species was higher in the lower zones of the river and diversity increased progressively downstream. The fish density in the channelized section was slightly lower than in the other two points. Also biomass in the channelized section was about a factor of 10 smaller than the calculated biomass in unaltered points. Moreover, in comparison with the unaltered sections of the river, in the channelized area a major decrease in the presence of fish larger than 150 mm was detected. The low shelter availability in the channelized section, lack of bank vegetation and alterations in the substratum could explain the observed variations in the length distribution, biomass and the lower value of the density of European minnow, Phoxinus phoxinus (Linnaeus, 1758).