不同频次刈割对羊草草原主要植物种群能量现存量的影响

对内蒙古羊草草原主要植物种群能量现存量对刈割频次响应的研究表明,在17年不同频次刈割干扰影响下,植物种群能量现存量随刈割频次的变化表现出不同的变化趋势,据此可以划分出3个不同的刈割响应类群：受抑种、耐刈种和受益种。受抑种包括羊草、羽茅、黄囊苔草、葱属植物和直根型杂类草; 耐刈种包括大针茅和冰草; 受益种包括洽草和糙隐子草。对于种群相对能量现存量而言,除羊草随刈割频次的增加呈显著下降趋势外,其他受抑种均随刈割频次的增加保持相对稳定,而受益种和耐刈种的相对值则随刈割频次的增加而呈增加趋势。同时,刈割对植物能量现存量的影响还表现在植物热值变化上,但变化幅度小于10%。     

温带草原与暖温带落叶阔叶林交错区植被建群种生态位研究——以山西恒山南北坡植被为例

在中国植被分区上,山西恒山是温带草原地带与暖温带落叶阔叶林地带的交错区。本文采用Shannon-Wiener 生态位宽度指数将南北坡群落的建群种群分别划分为3个生态类群。南坡的山蒿、小红菊、披针叶苔草、地榆,北坡的披针叶苔草、山菊、硬质早熟禾、麦瓶草、地榆占据较宽的生态位,生态位泛化比较明显。而南坡的鹅绒委陵菜、三裂叶绣线菊、虎楱子、沙棘,北坡的长芒草、碱茅、山蒿、珠芽蓼、铃铃香、三裂叶绣线菊、沙棘、青杨占据较窄的生态位,这与种群所处的具体生境密切相关。南坡16个建群种群构成的240个种对中有100个种对表现出生态位重叠,占整个种对的41.9%,表明恒山南坡16个种群间具有比较显著的生态位重叠。北坡21个建群种构成的420个种对中69个种对有生态位重叠,占整个种对的16.4%,说明这21个种群并不表现出显著的生态位重叠,各种群间生态位明显分离,说明不同种群利用资源的差异性比较显著。这主要是由于恒山南坡山势平缓,而北坡陡峭,南坡植被呈连续性分布,而北坡植被由于海拔高差大,植被垂直带谱中经常有断带现象,所以,生态位重叠现象比较少见。通过对南北坡建群种群的生态位宽度和生态位重叠的整体比较,可以比较客观的确立恒山作为温带草原地带与暖温带落叶阔叶林地带的分界。     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.