基于群落种间关系的桫椤植物保护策略研究进展

桫椤科植物是古老的孑遗植物,现存的桫椤天然群落极为罕见,为了解桫椤(Alsophila spinulosa)及桫椤科(Cyatheaceae)植物在生物群落的中生存与保育状态研究现状,本文通过搜集国内外关于桫椤及桫椤科植物相关文献进行研究。桫椤科植物分布于高温潮湿、光斑直射的生境,常以斑块状分布于常绿阔叶林林缘。现阶段,桫椤科植物保护面临的主要问题是生态旅游、毁林开荒、环境污染、药材的违法采摘和挖掘等,这导致桫椤科植物的生境遭受干扰和破碎,桫椤科植株数量下降。对桫椤科植物的保护方式主要有就地保护、迁地保护,分子生物学技术在桫椤科植物繁育中应用逐渐增加。生物和非生物因素制约着桫椤科植物的分布和多样性,其中,生物因素特别是种间关系对桫椤植物的生长发育和分布有着重要影响,从种间关系的视角出发探讨桫椤科植物的保护或许不失为新时代桫椤科植物保护的有效方式。讨论了桫椤植科物相关的种间关系：桫椤科植物-微生物互作、桫椤科植物-其他植物互作、桫椤科植物-动物互作,探讨了桫椤科植物面临灭绝的因素以及近年来桫椤科植物相关的保护策略及成效,为桫椤科植物的有效利用和保护提供一定理论基础。     

中国桫椤科植物叶绿体trnL内含子和trnL-trnF基因间隔区序列的系统发育分析

运用对PCR产物直接测序和克隆后测序的方法测定了蚌壳蕨科1种和桫椤科11种(其中桫椤分别测定19株：小羽桫椤测定2株)植物的叶绿体trnL基因内含子和trnL-trnF基因间隔区序列。12种植物相应的长度介亍l004-l082之间,A T平均含量60．9％,G C平均含量39．1％。计算了不同种间以及种内不同个体间序列的碱基差别(转换值／颠换值)和Kimura遗传距离。序列数据经排列后分别进行最简约法、最大似然法和邻接法分析,结果显示：(1)白桫椤、海南白桫椤和大羽桫椤构成的分支最早和该科内其余植物组成的另一分支分歧,而后者又进一步分为刃个亚分支,分别和桫椤亚属、黑桫椤亚属对应,支持夏群的分类处理：(2)大桫椤～狭羽桫椤～毛轴桫椤～篦齿桫椤、多羽桫椤一白桫椤～海南白桫椤以及小羽桫椤一桫椤各自构成独立、自然的末端分支,再参照分支内植物间的遗传距蔼取值,建议将此3个末端分支依次归并为3种：大桫椤、白桫椤和桫椤;(3)白桫椤属在科内处于基部位置,桫椤属奇桫椤亚属和黑桫椤亚属为衍生分支,赞同Tryon关于桫椤科进化和囊群盖起源的假说。     

广东阳春百涌自然保护区桫椤科植物资源调查

广东阳春百涌自然保护区属云开山脉,区内桫椤科植物资源丰富,但具体种类及其资源量并无准确资料,为此我们开展了相关野外调查和统计。调查表明,保护区内共有4种桫椤科植物,即桫椤Alsophila spinulosa、大叶黑桫椤Gymnosphaera gigantea、小黑桫椤G. metteniana和黑桫椤G. podophylla。依据保护区内桫椤科植物主要沿林道分布的特点,提出了按林道长度估算资源量的方法,据估算,保护区内有桫椤约900株,大叶黑桫椤约1.5万株,小黑桫椤约320株,黑桫椤约4500株。阳春百涌保护区是华南地区大叶黑桫椤的主要保存地。     

广西河池发现大片桫椤

最近,在广西河池市大山塘林场发现有大片的桫椤植物群落,多生于杉木人工林下,特别是在杉木林缘形成大面积桫椤群落,生长茂密(见右图)。据林场职工反映:该场建于1957年9月,当时营造杉木林时,林地都经过全垦整地,造林后又于1978年进行人工间伐,那时没有发现桫椤生长,但在间伐后;林地内有充分的光照,透光度达20％,气温暖和,湿度适中,为桫椤孢子传播、萌发及生长发育创造了有利条件,因而形成了杉木林下及林缘的桫椤植物群落。     

滇南桫椤的系统位置:来自叶绿体trnL内含子和DNA trnL-F间隔区序列的证据

为了探讨滇南桫椤Alsophilaaustroyunnanensis的系统位置 ,我们对该植物与中华桫椤Alsophilacostularis的叶绿体DNAtrnL内含子和trnL F间隔区序列进行PCR扩增和序列测定。滇南桫椤的trnL内含子、trnL F间隔区序列的长度分别为 5 70bp ,36 2bp ;中华桫椤的trnL内含子、trnL F间隔区序列的长度分别为 5 72bp ,36 1bp。结合已经发表的其他桫椤科植物的相应序列进行系统发育分析 ,用简约法和邻接法构建的系统发育树基本一致。结果表明 :1)所分析的桫椤科植物构成一个单系群 ;2 )滇南桫椤与Gymnosphaerapodophylla、Gymnosphaerapectinata、Gymnosphaerapseudogigantea、Gymnosphaeratinganensis、Gymnosphaeragigantea关系较近 ,聚成一支系 ;3)中华桫椤与Cyatheatsangii、Alsophilaspinulosa关系较近 ,聚成一支系。本文系统发育分析的结果支持将滇南桫椤归入黑桫椤属Gymnosphaera。     

桫椤濒危原因的探讨

本文观察了西双版纳生境下桫椤(Alsophila spinulosa (Hook.) Tryon)生物学特性。桫椤濒危的可能原因是:1.桫椤孢子寿命短,难萌发。2.孢子—原叶体—孢子体的生活周期长,并且在丝状体、原叶体和幼孢子体阶段,无特殊结构去抵抗和忍耐一切不利环境因子的影响。3.孢子萌发、形成配子和胚胎建成等过程对生境条件的要求严格,因此桫椤的分布受到很大的限制。在现代气候条件下,桫椤只能在温暖、湿润的热带、亚热带林地生存下来。一旦桫椤生栖的森林遭到破坏,桫椤随之死亡。4.桫椤是木本植物,生殖周期很长,不利于生存发展。5.桫椤根很不发达,树干内部的输导系统也较原始,只能适应空气和土壤湿润的生境。6.桫椤被人为的掠夺式的砍伐。针对以上情况,提出了保护这一种质资源的措施。     

画稿溪国家级自然保护区珍稀植物桫椤种群结构与更新

根据四川画稿溪国家级自然保护区桫椤(Alsophila spinulosa)种群分布特点,设立4个样地1个样带共44个样方(20 m×20 m),从种群密度、生命表和生境关联(草本层郁闭度和林分受干扰强度)等方面研究了保护区桫椤种群的结构特征。结果表明,每个桫椤种群样方的平均密度为0.088株/m2,幼苗密度为0.049株/m2;桫椤种群的死亡率和消失率曲线变化基本一致,发育过程中出现3个死亡高峰值,分别在第1龄级(H0.01 m)、第7龄级(3.90 m≤H4.80 m)和第10龄级(H≥6.60 m)阶段;种群生存率单调下降,累计死亡率单调上升,第7龄级以后,种群生存率小于1%;根据种群生存率函数Si、累计死亡率函数Fti、死亡密度函数fti和危险率函数λti4个生存函数曲线表明,画稿溪桫椤种群具有前期锐减、中期稳定、后期衰退的特点。桫椤各龄级阶段密度与草本层郁闭度均无显著相关(p≥0.18),然而桫椤幼苗(第1龄级)以上的个体密度、第7龄级密度与干扰度之间呈显著负相关(p0.05)。综合分析表明,画稿溪桫椤种群具有一定的自然更新能力,但人为活动的干扰可能是限制桫椤种群的因素之一。     

毛竹扩张对濒危植物桫椤根系形态可塑性的影响

为探讨毛竹(Phyllostachys heterocycla)向桫椤(Alsophila spinulosa)林扩张的根系形态可塑性变化,在赤水桫椤国家级自然保护区毛竹-桫椤混交林上分别设置受毛竹轻度、中度以及重度干扰的样地,用根钻法收集桫椤、毛竹根系并对其生物量密度、细根比根长、相邻同级侧根节点距等参数进行比对。结果表明:各干扰程度下桫椤根系生物量密度均远低于毛竹,且二者呈负相关;随着与毛竹的接近,桫椤根系生物量持续下降;各样地中毛竹细根比根长均高于桫椤;重度干扰下毛竹侧根节点距最小,侧根数目最多;且毛竹根系多分布于表层土壤。由此可见,桫椤根系逐渐趋向于分布在深层土壤,毛竹在向桫椤林扩张过程中可通过改变根系生物量密度、细根比根长、相邻同级侧根节点距等形态可塑性特征来占据优势。     

五指山热带雨林黑桫椤种群及其所在群落特征

黑桫椤(Alsophila podophylla)属国家二级保护植物.作者在海南岛五指山山地雨林和低地雨林分别设立样地对黑桫椤种群及其所在群落进行了调查,分析了热带雨林黑桫椤种群的年龄结构、空间分布格局、数量分布以及群落结构和物种多样性.结果表明,山地雨林和低地雨林中黑桫椤种群分别为稳定型种群和增长型种群,都是完全集群分布.低地雨林的黑桫椤平均密度是山地雨林的1.7倍.土壤pH值对黑桫椤种群密度有负的影响,全磷含量对其有正的影响.山地雨林林地土壤pH值大而全磷含量低,低地雨林刚好相反.土壤酸碱度和全磷含量的差异是导致两地黑桫椤数量差异的原因之一.pH值对黑桫椤平均密度的影响效应是全磷含量的2.5倍,说明pH值是影响黑桫椤种群密度的主要因素.黑桫椤所在群落垂直结构分为3个乔木亚层、2个灌木亚层及草本层.山地雨林黑桫椤所在群落的Simpson指数和Shannon-Wiener指数分别为0.957和5.305,均匀度为0.811;低地雨林黑桫椤所在群落的Simpson指数和Shannon-Wiener指数分别为0.937和5.484,均匀度为0.804.总之,五指山山地雨林和低地雨林的黑桫椤种群年龄结构、分布格局和数量分布都有一定差异,这些差异是由生境差异造成的.热带雨林黑桫椤所在群落结构复杂,物种多样性丰富.     

桫椤的潜在适生区及其变化

桫椤是极为珍贵的孑遗木本蕨类植物。本研究利用Maxent生态位模型研究其全球潜在适生区及其变化,并运用受试者工作特征曲线(ROC)验证了精度,以为其资源的保护、搜寻和引种栽培提供参考。结果表明: 桫椤的潜在适生区主要位于亚洲,少量分布于北美洲、中美洲和香草四岛、新西兰、新喀里多尼亚、斐济。当前气候条件下,桫椤的全球适生区总面积为357.1万km²,其中,亚洲占88.4%,中国占49.5%。桫椤在中国的高适生区主要分布在云贵高原、四川盆地、岭南和台湾岛。影响桫椤适生区分布的主导因子为最暖季降水量、7月平均降水量、温度季节性和昼夜温差月均值。在SSP1_2.6气候情景下,2041—2060年,桫椤全球潜在适生区面积预计减少7.8%,2081—2100年预计增加3.2%;在SSP2_4.5气候情景下,2041—2060和2081—2100年其面积预计分别增加2.9%和7.2%;在SSP5_8.5气候情景下,2041—2060和2081—2100年其面积预计分别增加3.3%和5.3%。     

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.     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

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.