三种正常与矮化植物的木材比较观察

本文比较观察了三种不同木材类型的正常与矮化树木的木材结构:针叶材的太白红杉(Larix chinensis Beissn.)、散孔材的辽东桤木(Alnus sibirica Fisch.)和环孔材的蒙古栎(Quercus mongolica Fisch.)。这些植物在个体发育过程中,各年的年轮宽度及管状分子长度、宽度等变化,存在各自的规律性。这些规律并不因生长环境的差异而变更。不过,逆境下生长的矮化植株的年轮宽度和管状分子的大小明显地比正常的要窄小,同时在木材结构的其它数量性状上,也有较大变化;然而,其各自的种属定性特征仍保持稳定。这些似乎可说明:生态环境的变化对木材结构的数量性状有较大影响,但是对木材种属的定性特征则无明显作用。     

肌细胞发育过程中间隙连接的变化

用石蜡切片、超薄切片和冰冻蚀刻技术研究了东方蝾螈胚胎肌细胞发育过程中间隙连接的变化。间隙连接最初出现于原肠后期的体节中胚层细胞中,到原肠末期,体节中胚层细胞间的间隙连接数量骤增,从神经板期到鼻窝出现期,间隙连接数量保持在一个相当高的水平,肌效应期后,其数量明显下降,直到肌细胞发育成熟,神经-肌肉连接充分发育,间隙连接才消失。间隙连接大小的变化与数量的变化表现为平行的现象。此外,细胞融合之前,正是间隙连接的数量和大小达到最高峰的时间。这些结果说明细胞通讯与胚胎肌细胞发育密切相关。对细胞通讯在细胞决定和分化以及细胞融合中的可能作用进行了讨论。     

不同植物在水分胁迫条件下脯氨酸的累积与抗旱性的关系

Ca植物春小麦幼苗叶片累积脯氨酸的数量随水分胁迫时间和强度递增,累积的数量与品种的抗旱性没有相关性。C_4植物玉米和高粱累积脯氨酸的数量低于小麦,但高粱多于玉米。CAM植物落地生根脯氨酸含量略有变化。旱生植物细枝岩黄芪的同化枝累积脯氨酸的数量高于中生植物钻天杨和槐的叶片,而梭梭的同化校则低于槐而高于钻天杨。表明这些植物累积脯氨酸的数量与它们的抗旱性无夫。因此似不宜用脯氨酸数量的多少作为植物抗旱性的生理指标。     

藏羚Y染色体雄性特异区遗传多样性

<正>遗传多样性反映了物种应对环境变化与进化的潜力,遗传多样性越高,对环境变化的适应能力就越强(沈浩和刘登义,2001)。对于经历过人类猎杀导致种群危机的野生物种,随着短时间内大量个体的消亡,很多潜在的优良基因单倍型也会丧失,在后续种群数量恢复过程中,这些单倍型并不会随着种群个体数量的增加而迅速恢复,即遗传多样性的恢复明显滞后于种群数量的恢复(Frankham et al., 2002)。     

日本血吸虫在小鼠体内发育形态的扫描电镜观察

日本血吸虫童虫在移行和发育过程中体形发生了明显的演变,并形成了口吸盘和排泄孔,同时也伴随着许多细微结构的改变。这些改变包括:体褶和体嵴数量及高度的增加、体棘数目和位置的改变、感觉器数量和分布的变化。     

两栖类种群数量下降原因及保护对策

近几十年来 ,全球范围内的两栖类出现了较快的种群数量下降 ,包括部分物种的灭绝。引起两栖类种群数量下降的原因可能有 :紫外线辐射、生境破碎和改变、生物入侵和捕食、环境污染、疾病、气候变化以及这些因素的相互作用 ,其中生境破碎和改变是主要原因 ,而引起各因素变化的全球变化可能是根本原因。应加强对两栖类种群动态的研究 ,探明其下降机制 ,制定相应的保护对策 ,减少两栖类的下降     

大型哺乳动物的趋势监测:青海野牛沟和甘肃阿克塞国际狩猎场的案例

大型野生动物种群数量估算的理想条件是使用数学模型以及严格的实验设计来选择样本。可是,野外条件状况往往违背数学模型假设前提,不可能随机地选择样本。于是,计算的结果不但不可靠,而且很可能没有意义。就野生动物管理来说,不需要获得一个准确的种群数量,只需一个长期的数量趋势,就足以指导相关管理工作。在中国大型哺乳动物长期监测还没有纳入常规。本文报道了位于青海省野牛沟和甘肃省阿克塞县两个野生有蹄类动物种群数量的长期趋势监测项目。我们这些年里一直用相同的方法持续监测,并明确了监测数值结果包含有不确定性。尽管存在不确定性,仍可以发现监测地点野生有蹄类动物种群变化趋势,这些结果可以帮助野生动物管理者据此变化及时作出相应管理计划。     

性诱剂对小菜蛾种群控制的应用技术研究

应用扩展的均匀设计,探讨了不同蔬菜种类、不同小菜蛾卵量基数和不同性诱剂诱盆数量等条件下小菜蛾性诱剂的控制效果.结果表明,小菜蛾卵量基数和诱盆数量的变化是影响控制效果的主要因素,而蔬菜种类的作用较小;同时建立了控制效果与这些因素之间变化的动态模型.通过对该模型的分析和模拟,建立了田间不同条件下性诱剂的定量化应用技术.     

海南清澜港红树林湿地鸟类初步研究

记录到清澜港红树林湿地鸟类52种,隶属于19科9目。其中水鸟31种,陆生鸟类21种;留鸟29种,迁徙鸟类23种。在这些鸟类中有国家二级保护鸟类3种,中日候鸟协定名录中的鸟类17种,中澳候鸟协定名录中的鸟类18种。清澜港鸟类物种数量存在季节变化,无论是从总的鸟类种类看,还是从水鸟种类看,都是以冬季鸟类种数最多,而夏季鸟类种数最少,年变化趋势是：冬季＞秋季＞春季＞夏季。鸟类物种数量季节变化的最重要原因是迁徙鸟类的周年变化。不同栖息地的食物条件和滩涂面积不同,鸟类的组成和数量也不同。本文还对清澜港鸟类的多样性进行了分析。     

紫外线对黑尾果蝇的生物学效应

野生型黑尾果蝇经紫外线连续处理3代,随着照射时间延长,每代均表现显著的生物学效应。这些生物学效应主要是子代数量减少,羽化延续时间缩短,体重减轻,而且有致略效应和间接的诱变效应。但处理后的子代性别比例变化不大。     

Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula shelf

During the past ten years, the Antarctic Peninsula has been identified as the most rapidly warming region of the Southern Hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past. Many biological proxies, such as marine diatom assemblages, have been used to determine Southern Ocean palaeoceanographic conditions during the Late Quaternary, however, few investigations have attempted to link observations of modern floras with the fossil record. In this study we examine a suite of modern austral spring (December 2003) and summer (February 2002) surface water samples from along the western Antarctic Peninsula (WAP) continental shelf and compare these to core-top, surface sediment samples. Using detrended correspondence analysis (DCA) and principal component analysis (PCA) of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record. This multivariate analysis reveals that our modern assemblages can be divided into three groups: summer southern WAP sites, summer northern WAP sites, and spring WAP sites. Sea surface temperature (SST) is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer, but sea surface salinity (SSS) is more important for understanding temporally-equivalent regional variations in assemblage. Our summer diatom samples are more reminiscent of early season assemblages, reflecting the unusually late sea ice retreat from the region that year. When the modern assemblages are compared to the fossil record, it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments, and that the fossil record more closely reflects spring assemblages. This observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the WAP during the Late Quaternary and highlights the need for many more such studies in order to address longer timescales, such as interannual variability, in the context of the fossil record.     

A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

东海南部陆缘(莆、泉段)全新世沉积硅藻

对东海南部陆缘莆田、泉州地区两口钻井岩芯系统的沉积硅藻研究,共发现33属117种（或变种）硅藻化石,根据剖面硅藻组合特征的变化,结合计算机的对应分析结果划分了硅藻带,建立该区全新世的7个硅藻组合序列,恢复当时古环境演变的7个阶段,填补该区沉积硅藻系统研究的空白,丰富了海陆过渡沉积硅藻的研究。     

Modern and fossil diatom assemblages from Bol’shoy Lyakhovsky Island (New Siberian Archipelago,Arctic Siberia)

This article discusses the results of a taxonomic and ecological investigation of diatoms from polygonal ponds and Quaternary permafrost deposits of Bol’shoy Lyakhovsky Island (New Siberian Archipelago) and the reconstruction of climatic changes on the Island during late Pleistocene/Holocene transition using fossil diatom assemblages from the permafrost deposits. The taxonomic list of diatoms includes 159 diatom species. The main ecological factors that determine the distribution of diatoms in the investigated data set are mean July air temperature, рН, electrical conductivity, water depth, and concentrations of Si⁴⁺ and Al³⁺. An increase in water depth and stable lacustrine conditions in the Lateglacial–Holocene in the ancient thermokarst lake relate to Lateglacial warming before 11860 ± 160 years BP and during the early Holocene between 11210 ± 160 and 7095 ± 60 years BP.     

THE POSSIBLE OCCURRENCE OF PHOTOSYNTHETIC MICROORGANISMS IN DEEP-SEA SEDIMENTS OF THE NORTH ATLANTIC1,2,3

An assemblage of 12 diatom species and other photosynthetic microorganisms associated with red clay sediments collected from a depth of 6150 m in the North Atlantic was observed to bloom in Antarctic bottom water when exposed to sunlight at sea surface temperature. Although no growth could be detected over the first 3 days of the experiment, nitrate was nearly completely stripped from the water. The maximum growth rate of 4.7 doubling/day was reached between days 4 and 5. Most of the diatom species have been described as littoral or coastal forms, and it is suggested that these organisms are transported to depth by fecal material, turbidity currents, or a combination of the two.     

DISTRIBUTION OF DIATOMS IN THE PLANKTON OF YAQUINA ESTUARY,OREGON1

The distributional patterns of diatoms in the plankton of the Yaqnina Estuary, Oregon, were, investigated and related to selected climatic and hydrographic factors. Distribution was strongly influenced by seasonal patterns of rainfall resulting in the introduction of a large volume of fresh water into the estuary during fall and winter. Plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change in species composition than in winter. Winter assemblages were further characterized by many pennate diatoms, apparently dislodged from the benthos during periods of high freshwater discharge and silt loads. A statistical measure of community difference indicated an increase in taxonomic homogeneity among assemblages throughout the estuary with the onset of the rainy season in late fall and a gradual transition to a more heterogeneous system again during late spring. Canonical correlation ordered 20 prominent diatom taxa along the salinity gradient and identified possible relationships among certain taxa and selected environmental variables, namely visible light energy and temperature. Redundancy in the species data given the environmental data was only 40%, emphasizing the difficulty in demonstrating a quantitive relationship between plankton dynamics in the field and concurrent measurements of chemical and physical variables.     

南极乔治王岛燕鸥湖晚第四纪硅藻（Ⅲ）：Diatomales，Achnanthales和Surirellales

本文对南极乔治王岛燕鸥湖晚第四纪硅藻中的等片藻目（Ｄｉａｔｏｍａｌｅｓ）、曲壳藻目（Ａｃｈｎａｎｔｈａｌｅｓ）和双菱藻目（Ｓｕｒｉｒｅｌｌａｌｅｓ）进行了系统分类描述,计有２４个种和８个变种,其中包括１个新种,５个新变种。它们可归属于：１）世界普生种,淡水或半咸水生境,中性－偏碱性;２）南极近岸浅海海域中常见种。     

THE IMPORTANCE OF DIATOM CELL SIZE IN COMMUNITY ANALYSIS1

The large variation in size and shape in diatoms is shown by morphometric measurements of 515 benthic and pelagic diatom species from the Baltic Sea area. The largest mean cell dimension (mostly the apical axis) varied between 4.2 and 653 μm, cell surface area between 55 and 344,000 μm², and cell volume between 21 and 14.2 × 10⁶μm³. The shape‐related index, length to width ratio, was between 1.0 and 63.3 and the shape‐ and size‐related index, surface area to volume ratio, was between 0.02 and 3.13. Diatom community analysis by multivariate statistics is usually based on counts of a fixed number of diatom valves with species scores irrespective of cell size. This procedure underestimates the large species for two reasons. First, the importance of a species with higher cell volume is usually larger in a community. Second, larger species usually have lower abundances and their occurrence in the diatom counts is stochastic. This article shows that co‐occurring small and large diatom species can respond very differently to environmental constraints. Large epiphytic diatoms responded most to macroalgal host species and small epiphytic diatoms most to environmental conditions at the sampling site. Large epilithic diatoms responded strongly to salinity, whereas small epilithic diatoms did so less clearly. The conclusion is that different scale‐dependent responses are possible within one data set. The results from the test data also show that important ecological information from diatom data can be missed when the large species are neglected or underestimated.     

Surface lithofacies,biofacies, and diatom diversity patterns as models for delineation of climatic change in the southeast Atlantic Ocean

Distribution of diatom species in surface sediments of the southeast Atlantic Ocean is regulated by present-day oceanographic and hydrodynamic processes. Five assemblages (vectors) defined by factor-vector analysis, reflect different environments and conditions. Assemblage A is a high diversity flora associated with the nutrient-rich, relatively cold waters south of the Polar Front in the diatom ooze belt. Occurrence of this flora on Maud Rise and vicinity may reflect periodic occurrence of a polynya in that area. Assemblage B is a reworked assemblage that dominates the southern portion of the study area. Productivity there is low, reflecting sea ice cover during most of the year. The area north of the Polar Front is dominated by Assemblage C, whose characteristic species reflect the relatively warm Subantarctic Surface Water. Winnowing and frustule breakage have altered Assemblage D (found in three isolated samples) by removing relatively delicate forms leaving lag deposits of more robust species. Assemblage E is a low diversity stress flora, reflecting unstable, unpredictable environments along the Polar Front, Antarctic slope, and the northern boundary of winter sea ice. These sites are characterized by the sinking of cold water. Downcore analysis of cores lying adjacent to the Polar Front and the diatom ooze—pelagic clay boundary show evidence for past climatic variation. The low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality, make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations. The position of the Polar Front has migrated at least three times within the last 0.015 m.y. B.P. Within the last 0.3 m.y. B.P. warm maxima have occurred at approximately 0.0, 0.015, 0.125 and 0.3 m.y. B.P.     

Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the late Quaternary

The available ecological and palaeoecological information for two sea ice-related marine diatoms (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, suggests that these two species have similar sea surface temperature (SST), sea surface salinity (SSS) and sea ice proximity preferences. From phytoplankton observations, both are described as summer or autumn bloom species, commonly found in low SST waters associated with sea ice, although rarely within the ice. Both species form resting spores (RS) as irradiance decreases, SST falls and SSS increases in response to freezing ice in autumn. Recent work analysing late Quaternary seasonally laminated diatom ooze from coastal Antarctic sites has revealed that sub-laminae dominated either by T. antarctica RS, or by P. glacialis RS, are nearly always deposited as the last sediment increment of the year, interpreted as representing autumn flux. In this study, we focus on sites from the East Antarctic margin and show that there is a spatial and temporal separation in whether T. antarctica RS or P. glacialis RS form the autumnal sub-laminae. For instance, in deglacial sediments from the Mertz Ninnis Trough (George V Coast) P. glacialis RS form the sub-laminae whereas in similar age sediments from Iceberg Alley (Mac.Robertson Shelf) T. antarctica RS dominate the autumn sub-lamina. In the Dumont d'Urville Trough (Adélie Land), mid-Holocene (Hypsithermal warm period) autumnal sub-laminae are dominated by T. antarctica RS whereas late Holocene (Neoglacial cool period) sub-laminae are dominated by P. glacialis RS. These observations from late Quaternary seasonally laminated sediments would appear to indicate that P. glacialis prefers slightly cooler ocean–climate conditions than T. antarctica. We test this relationship against two down-core Holocene quantitative diatom abundance records from Dumont d'Urville Trough and Svenner Channel (Princess Elizabeth Land) and compare the results with SST and sea ice concentration results of an Antarctic and Southern Ocean Holocene climate simulation that used a coupled atmosphere–sea ice–vegation model forced with orbital parameters and greenhouse gas concentrations. We find that abundance of P. glacialis RS is favoured by higher winter and spring sea ice concentrations and that a climatically-sensitive threshold exists between the abundance of P. glacialis RS and T. antarctica RS in the sediments. An increase to > 0.1 for the ratio of P. glacialis RS:T. antarctica RS indicates a change to increased winter sea ice concentration (to >80% concentration), cooler spring seasons with increased sea ice, slightly warmer autumn seasons with less sea ice and a change from ~ 7.5 months annual sea ice cover at a site to much greater than 7.5 months. In the East Antarctic sediment record, an increase in the ratio from <0.1 to above 0.1 occurs at the transition from the warmer Hypsithermal climate into the cooler Neoglacial climate (~ 4 cal kyr) indicating that the ratio between these two diatoms has the potential to be used as a semi-quantitative climate proxy.