青藏高原东部橐吾属三种植物的繁育系统

研究青藏高原东缘分布的箭叶橐吾、黄帚橐吾和掌叶橐吾的繁育系统,箭叶橐吾和黄帚橐吾各自居群中有性生殖和克隆繁殖的权衡关系,分析三种植物的的克隆繁殖与生态适应,探讨橐吾属植物对高寒环境胁迫条件下的适应与进化。结果显示三种橐吾的花果期在6月中旬到10月初,花序为头状花序组成的总状排列。三种橐吾的杂交指数(OCI)均为4,繁育系统以远交为主、部分自交亲和、虫媒、需要传粉者;影响有性生殖成功的因素除昆虫侵食以外,黄帚橐吾和箭叶橐吾低的结实率主要原因是传粉媒介限制。限制结实的主要因素是高寒多风的环境限制了昆虫的活动,访花昆虫数量减少,从而使花粉转移效率降低,导致了低的结实率。植物采取的适应对策:大量开花,延长雌雄配子体的功能期和传粉媒介的泛化等,可见三种橐吾有性生殖的潜力依然很大。箭叶橐吾和黄帚橐吾在自然条件下主要进行有性生殖,在保护草场时,应针对其有性生殖器官采取措施。     

同域分布共享传粉者的鼠尾草属植物的生殖隔离

生殖隔离是生物多样性产生的重要原因之一,不同物种间的生殖隔离形成阶段、方式和强度不完全相同。为了揭示生殖隔离在鼠尾草属(Salvia)物种多样性产生和维持过程中的作用和特点,本文研究了浙江天目山同域分布的舌瓣鼠尾草(S.liguliloba)和南丹参(S.bowleyana)的开花、传粉和生殖隔离,利用人工授粉和杂交实验检测它们的种间遗传相容程度。结果表明,在花的形态结构、花及花序的生长、着生方式与数量特征上,2种鼠尾草属植物均差异显著(P0.05)。2种鼠尾草属植物共享同一种有效传粉昆虫——三条熊蜂(Bombus trifasciatus),但通过访花行为的显著差异和明显不同的花粉落置部位,有效避免了异源花粉干扰。人工杂交授粉的结果表明2个物种间遗传相容性较高,互为亲本的杂交结实率分别达到77.8±10.7%和78.7±11.2%。我们的研究表明,同域分布、花期重叠且共享唯一传粉者的2种鼠尾草属植物,以花部的传粉结构和传粉部位的差异,产生了较高程度的传粉前生殖隔离,避免了物种间的异源花粉干扰和自然杂交,保障各自较高的繁殖成效,以维持自然种群的多样性和遗传结构的稳定。     

黄帚橐吾对高寒草甸凋落物分解及氮释放的影响

受过度放牧等干扰因素的影响,黄帚橐吾(Ligularia virgaurea)在高寒草甸逐渐扩张成为优势种而被称为“退化指示种”,从而威胁生态系统功能和养分循环。然而,黄帚橐吾扩张引起的凋落物比例增多,对分解及养分释放的影响尚不清晰。凋落物分解连结着生态系统碳、氮循环,对于系统功能维持具有重要意义。本试验在三江源区黄帚橐吾为优势种的高寒草甸中,设置黄帚橐吾和其他物种凋落物的多梯度混合分解试验,测定黄帚橐吾和其他物种凋落物的重量损失和氮释放,分析黄帚橐吾生物量增多对凋落物分解的影响。结果表明：(1)分解1年后,黄帚橐吾重量损失及氮素释放较其他物种更缓慢;(2)随着黄帚橐吾生物量比例的增加,凋落物整体重量损失及氮素释放显著降低;(3)混合凋落物中黄帚橐吾能限制其他物种的分解,这种拮抗效应进一步延缓了混合凋落物的分解。综上,高寒草甸黄帚橐吾扩张引起的凋落物生物量增多通过延缓凋落物分解及氮释放,阻碍土壤养分输入,进而对草地碳氮循环过程产生不利影响。     

水稻籼粳亚种间组合合子前生殖隔离及其与杂种育性的关系

生殖隔离对新物种形成和维系至关重要,其作用机制是生命科学的核心科学问题之一.水稻籼粳亚种间存在生殖隔离现象.迄今为止,对水稻籼粳亚种间合子前生殖隔离机制的研究还不够深入.本研究选用籼稻、粳稻和广亲和品种在内的12个品种,进行亚种间、亚种内和带广亲和基因的亚种间17个组合的杂交实验.通过扫描电子显微镜观察花粉在柱头上的附着,发现2/3的亚种间杂交组合柱头平均附着花粉粒数不足5粒,存在较强的合子前生殖隔离现象;3/4的亚种内杂交组合附着花粉粒数多于5粒;所有的带广亲和基因的亚种间杂交组合附着花粉粒数均大于5粒.同时观察到亚种间杂交花粉管伸长多出现空瘪、盘绕等异常现象,亚种内及带广亲和基因的亚种间组合比较正常.研究还发现,杂交组合花粉附着量与其F1育性不相关,说明合子前与合子后生殖隔离是两个独立的事件.水稻籼粳亚种间通过花粉粒亲和性和萌发状态的差异阻碍杂种后代的产生,该现象是合子前生殖隔离的表现形式.研究结果有助于进一步理解生殖隔离的机制,同时对杂种优势的利用具有一定启发意义.     

典型黄帚橐吾型退化草地形成过程中土壤和植被特征

为深入了解典型毒草型退化草地形成的过程，本文对青藏高原原生草地上黄帚橐吾逐渐扩张形成典型毒草型退化草地过程中植被和土壤特征进行研究。结果表明：黄帚橐吾型退化草地形成过程中，黄帚橐吾种群密度、株高、盖度和生物量均增加；相比原生草地，退化草地的总地上生物量增加113.9%,土壤全氮、铵态氮、有机碳和速效磷含量分别增加61.0%、77.9%、45.3%和78.8%,土壤微生物生物量碳、氮分别增加42.1%和47.4%,而土壤硝态氮含量和物种丰富度分别减少40.1%和28.5%,除黄帚橐吾以外其他植物的生物量减少45.7%。黄帚橐吾极强的种间抑制能力、形态可塑性、高效的养分蓄积能力和利用效率是其成功扩张的关键，促进了黄帚橐吾型退化草地的形成。     

黄帚橐吾种群扩张对土壤理化特性与微生物功能多样性的影响

黄帚橐吾(Ligularia virgaurea)是高寒草甸退化的指示物种, 其种群扩张已严重影响了草地生态系统的经济服务功能, 但目前仍不明确土壤微生物是否参与了黄帚橐吾的种群扩张。该研究依托兰州大学高寒草甸试验站, 选择了4个不同密度的黄帚橐吾斑块, 分析了黄帚橐吾种群扩张对该草甸土壤微生物功能多样性的影响。结果显示: 黄帚橐吾种群扩张虽然提高了土壤微生物活性, 但降低了土壤速效氮浓度。各斑块间土壤微生物Shannon指数、碳源利用种类、均一度指数均无显著差异, 但高密度斑块的土壤微生物碳源利用结构与对照斑块有显著差异。表明黄帚橐吾分布地土壤微生物功能多样性的改变所引起的土壤氮素限制是黄帚橐吾种群数量急剧增加的机制之一。     

Effects of the spreading of Ligularia virgaurea on soil physicochemical property and microbial functional diversity

黄帚橐吾(Ligularia virgaurea)是高寒草甸退化的指示物种, 其种群扩张已严重影响了草地生态系统的经济服务功能, 但目前仍不明确土壤微生物是否参与了黄帚橐吾的种群扩张。该研究依托兰州大学高寒草甸试验站, 选择了4个不同密度的黄帚橐吾斑块, 分析了黄帚橐吾种群扩张对该草甸土壤微生物功能多样性的影响。结果显示: 黄帚橐吾种群扩张虽然提高了土壤微生物活性, 但降低了土壤速效氮浓度。各斑块间土壤微生物Shannon指数、碳源利用种类、均一度指数均无显著差异, 但高密度斑块的土壤微生物碳源利用结构与对照斑块有显著差异。表明黄帚橐吾分布地土壤微生物功能多样性的改变所引起的土壤氮素限制是黄帚橐吾种群数量急剧增加的机制之一。     

新疆党参的花部综合征与次级花粉呈现

次级花粉呈现是植物提高花粉输出和接受的效率与准确性以及促进异交的一种繁殖策略.新疆党参(Codonopsis clematidea)具有典型的次级花粉呈现特性.本文采用野外观测、授粉实验与室内显微观测等方法,对该物种的花部综合征及其次级花粉呈现过程进行了详细观测,并对这些特征的适应意义进行了探讨.结果表明:新疆党参钟状下垂的蓝色花冠及黑黄色蜜腺,不仅避免了雨水冲刷雌雄蕊、稀释花蜜以及风移出花粉等不利影响,还增加了对传粉者的吸引,延长了花粉活力及柱头可授性持续时间.次级花粉呈现属于亚顶端花柱呈现者,呈现机制为沉积机制.该特性限制了单个传粉者带走的花粉量,延长了花粉呈现时间,使更多传粉者参与传粉过程,增加了雄性适合度.其雄性先熟及雌雄蕊空间位置变化,避免了雌雄功能干扰,为传粉者取食花蜜、输出花粉以及柱头接受异源花粉提供了通道和机会.其泛化传粉系统的主要传粉昆虫为林野熊蜂(Bombus silvarum)、草地熊蜂(B.paradoxus)和树长黄胡蜂(Dolichovespula sylvestris),其较长的单花花期(6 d左右),昆虫访花高峰期与花粉活力最高时期及柱头最佳授粉期相吻合,以及较大的泌蜜量、较高的花蜜糖浓度和较长的泌蜜时间等特征,可提高传粉者的访花频率,增加成功传粉的机会和传粉效率.在气候多变的天山山区,该物种特殊的花部综合征和次级花粉呈现机制对提高其传粉效率并促进异交繁殖成功具有重要意义.     

土著入侵种黄帚橐吾的替代防控展望

黄帚橐吾是青藏高原高寒草场中分布最广、危害极大的优势毒草,严重影响了该地区群落结构和草地畜牧业的发展。在介绍土著入侵种和替代防控概念及相关研究进展的基础上,针对黄帚橐吾目前缺乏高效经济生态防控措施的现状,结合国内外对入侵植物进行替代防控的经验与原则,提出了对黄帚橐吾进行替代防控的生态防控设想和黄帚橐吾替代植物选用的基本原则,初步划定了防控黄帚橐吾的替代植物范围。通过引种或者驯化乡土草种,在青藏高原培育禾本科、豆科植物或者建植禾豆混播人工草地,使其具备替代防控黄帚橐吾的潜力。     

5种地黄花部综合特征与繁育系统的初步研究

生殖隔离是物种分化与延续的基础,地黄属植物是否存在生殖隔离仍不清楚。通过实地观测地黄属5个物种(天目地黄、湖北地黄、裂叶地黄、地黄和茄叶地黄)自然种群的花部形态、开花动态、花蜜体积、花蜜的糖浓度及其日变化、杂交指数、花粉-胚珠比等指标,结合人工授粉套袋,对地黄属植物的花部综合特征和繁育系统进行研究。结果显示:(1)地黄属植物的花为两性花,单花花期5～7 d,种群花期40～60 d;5种地黄在花序类型、花形态、花粉量、花粉-胚珠比等方面都存在差异,其中茄叶地黄的花粉完全败育。(2)5种地黄属植物的繁育系统属于异交,部分自交亲和,需要传粉者,不具有无融合生殖特性,地黄与茄叶地黄存在强烈营养繁殖。(3)5种地黄属植物的花朵基部有蜜腺可以产生糖浓度较高的花蜜,这也支持传粉者的存在,但除地黄确定为蜜蜂传粉外,其它地黄植物在野外并未观测到有效的传粉者,可能与地黄的散生特性、生境相互隔离以及传粉观测期气象条件恶劣有关。研究认为,5种地黄属植物较长的花期能有效弥补传粉者访问频率低的不足;除遗传屏障外,推测地黄属5个物种花展示方式的差异可能吸引不同的传粉者,加之地理、生态因素的作用导致了5种地黄属植物繁育系统的分化。     

Pollen-stigma interference in two gynodioecious species of Lamiaceae with intermediate individuals

BACKGROUND AND AIMS: Intermediate individuals (perfect flowers with very high degree of pollen abortion) in a gynodioecious plant species are very rare. A study is made of male-female relationships in each flower type and how floral characters can enhance the avoidance of 'pollen discounting' and 'self-pollination' in two gynodioecious species, Teucrium capitatum and Origanum syriacum. METHODS: The relationship between stigma receptivity and pollen viability was studied in two gynodioecious protandrous species of Lamiaceae, in addition to measuring some floral morphological characters over the life span of the flowers. KEY RESULTS: Three plant types in each species were found: plants bearing hermaphrodite (or male fertile) flowers (MF), female (or male sterile) flowers (MS) and intermediate flowers (INT). Plant types differed in flower size, with MS types being shorter than the other two types. There was no difference in style length among plant types in T. capitatum. Stigma receptivity decayed with floral age and was negative and significantly correlated with pollen viability in the two species, and positive and significantly correlated with style length in O. syriacum but only in MS flowers of T. capitatum. CONCLUSIONS: Reduction in size of floral characters is associated with male sterility, except style length in T. capitatum. MF flowers have two successive reproductive impediments: self-pollination and pollen-stigma interference. In both species, self-pollination is avoided by dichogamy (negative correlation between stigma receptivity and pollen viability), and pollen-stigma interference shows two different patterns: (1) style elongation in O. syriacum is characterized by a significant length increase, final MF dimensions are greater than those of MS dimensions, and style length is positively and significantly correlated with stigma receptivity; and (2) style movement in T. capitatum is characterized by a non-significant increase in style length, final MF floral dimensions are similar to those of MS dimensions, and there is no correlation between style length and stigma receptivity.     

花粉外被蛋白B类小肽, 花粉打开柱头大门的一把钥匙

植物有性生殖过程中, 花粉-柱头间的识别作用是确保亲和花粉萌发、完成受精并保持后代遗传稳定性的重要环节, 也是农业生产上杂交育种的一个障碍。相关研究历来备受关注。然而, 经过几十年的研究, 亲和花粉如何被识别仍是未解之谜。最近, 华东师范大学李超团队的研究成果, 揭示花粉外被B类小肽PCP-Bs与柱头分泌的RALF23/33小肽竞争性地与柱头乳突细胞质膜上的ANJ-FER受体激酶复合体直接结合, 通过下游RAC/ROP-NADPH氧化酶信号途径调节柱头活性氧水平, 从而调节亲和花粉水合作用的机制。这一发现是认识花粉与柱头识别机制的重要突破。     

珍稀濒危植物细果秤锤树开花生物学特性和繁育系统

为了解珍稀濒危植物细果秤锤树（Sinojackia microcarpa）开花特征和有性繁殖,对其花部形态特征、开花动态、花粉胚珠比（P/O）、柱头可授性、花粉活力、套袋试验、访花昆虫及访花频率进行观测。结果表明：（1）细果秤锤树的杂交指数（OCI）为4,单花期5~7 d,种群花期可持续20 d左右。花粉与胚珠比为4 093.21±498.56。开花后第3天的花粉活力最高（76.21%）,而开花后第7天时花粉活力较低（18.37%）。细果秤锤树柱头最适可授期在开花后第2天。（2）套袋试验表明,细果秤锤树存在部分自交不亲和性,同时不存在无融合生殖,传粉昆虫是其完成生殖过程所必需的,且异株授粉能够提高其坐果率和结籽率。细果秤锤树的访花昆虫有3目5科7种,主要访花昆虫有黄胸木蜂（Xylocopa appendiculata）、熊蜂（Bombus sp.）、胡蜂（Vespa sp.）、中华蜜蜂（Apis cerana）、黑带食蚜蝇（Episyrphus balteatus）、其中熊蜂平均访花频率最高,达（8.67±0.21） 次·h^-1。对该物种开花生物学特征与繁育系统进行深入研究,有利于进一步探究其濒危机制,为后续珍稀濒危植物的研究提供理论依据和参考。     

Potential Risk of Hybridization in Ex Situ Collections of Two Endangered Species of Sinojackia Hu （Styracaceae）

Spontaneous hybridization in ex situ facilities can undermine the genetic integrity of ex situ collections and potentially contaminate open-pollinated seeds or seedlings destined for the reintroduction of endangered plant species into the wild. In the present study, the potential risk of hybridization between two endangered Chinese endemic species, namely Sinojackia xylocarpa Hu and S. rehderiana Hu, which are naturally allopatric species but were conserved ex situ in Wuhan Botanical Garden （WBG）, Wuhan, China, were investigated over three consecutive years from 2003 to 2005. The entire overlapping flowering period of the two species was 14-20 d and the two species shared the same pollinator insects during the entire flowering season in WBG. The floral isolation between the two species was not an issue in the ex sltu collection at WBG. The results suggest an opportunity for pollen transfer between species and a potential risk of genetic Introgression and loss of genetic identity of open-pollinated seeds produced in the ex sltu Collection of these two endangered species. An artificial reciprocal cross between S xylocarpa and S. rehderlana confirmed that the two congener species could readily set seeds, indicating no post-pollination barriers to hybridization and the importance of spatial isolation as a barrier to inter-specific crossing. Therefore, to manage these crossable species with overlapping flowering times and shared pollination vectors in ex situ facilities, spatial isolation should be carefully considered to minimize the possibility of spontaneous hybridization.     

Incomplete reproductive isolation between Rhododendron taxa enables hybrid formation and persistence

The evolutionary consequences of hybridization ultimately depend on the magnitude of reproductive isolation between hybrids and their parents. We evaluated the relative contributions of pre-and post-zygotic barriers to reproduction for hybrid formation, hybrid persistence and potential for reproductive isolation of hybrids formed between two Rhododendron species,R. spiciferum and R. spinuliferum. Our study established that incomplete reproductive isolation promotes hybrid formation and persistence and delays hybrid speciation.All pre-zygotic barriers to reproduction leading to hybrid formation are incomplete: parental species have overlapping flowering; they share the same pollinators;reciprocal assessments of pollen tube germination and growth do not differ among parents. The absence of post-zygotic barriers between parental taxa indicates that the persistence of hybrids is likely. Reproductive isolation was incomplete between hybrids and parents in all cases studied, although asymmetric differences in reproductive fitness were prevalent and possibly explain the genetic structure of natural hybrid swarms where hybridization is known to be bidirectional but asymmetric. Introgression, rather than speciation, is a probable evolutionary outcome of hybridization between the two Rhododendron taxa. Our study provides insights into understanding the evolutionary implications of natural hybridization in woody plants.     

宁夏枸杞传粉生态学初步研究

田间观察检测了宁夏枸杞(Lycium barbarum L.)9个品系的开花物候、开花动态、花粉活力、柱头可授性及其繁育系统,并对花粉萌发、花粉管生长以及访花者的种类和访花行为进行了初步研究.结果表明,宁夏枸杞整个居群有长达5个月的花期,单花的花期仅为3～4 d,花粉活力可保持15 d左右,柱头可授性在72 h左右,雌雄生殖单位在持续时间上有较长的相遇期;花粉数量与胚珠比(P/O)为4 000左右,杂交指数(OCI)介于3或4,繁育系统为异交型,需要传粉者;荧光显微观察表明,参试的3个品系的花粉均能在柱头上萌发,2个有自交不亲和现象,其位置发生在花柱的上半部分和子房内.访花昆虫有17种,分属双翅目、膜翅目和鳞翅目,花的结构和开花式样适合以意大利蜜蜂和食蚜蝇为主的多种昆虫传粉.     

Experimental sympatry suggests geographic isolation as an essential reproductive barrier between two sister species of Pedicularis

Although mechanical isolation mediated by shared pollinators has been considered as a classic model of pollinator-mediated floral isolation in Pedicularis, a superdiverse genus in Hengduan Mountains, southwest China, there has been no empirical study of interspecific pollen flow between closely related species. We examined reproductive barriers at six different stages between Pedicularis cranolopha and Pedicularis tricolor, two sister species. The two sister species were geographically isolated from each other based on our field survey and the records of herbarium specimens. Translocation experiments showed that flowering phenology partly overlapped and bumblebee pollinators did not discriminate between flowers of the two species. Bumblebee interspecific moves could mediate interspecific pollination as traced using fluorescent powder, in which pollen analogs placed on one species were transferred to the stigmas of the other species in experimental plots containing both species. Heterospecific pollen tubes grew in the style as well as conspecific pollen in hand-pollination experiments. Reciprocal hybridization between the two species could produce (partially) viable seeds, suggesting weak post-pollination barriers. Our results showed that geographic isolation was an important barrier of two species, and the total reproductive isolation between two species was incomplete when without geographical isolation. The formation of Big Snow Mountains could introduce an important pre-zygotic reproductive barrier between the two sister species of Pedicularis; such geographical isolation could be responsible for allopatric speciation, giving a clue to understanding the rapid radiation on mountain areas.     

牛耳朵传粉生物学研究

苦苣苔科(Gesneriaceae)报春苣苔属(Primulina Hance)是一个近年来备受关注的类群,其纷繁复杂的物种多样性和属下种间的特有分布引起了分类学家和植物学研究者的极大兴趣。该属除了极少数的物种如牛耳朵[(Primulina eburnea (Hance) Y. Z. Wang)]以外,绝大部分的物种为狭域分布或地方特有种,其分布范围很窄。为了揭示牛耳朵的传粉生物学和繁育系统对其生殖过程和拓殖能力的影响机制,作者系统地研究了牛耳朵的开花物候、花粉与柱头活性、访花昆虫的种类和访花行为、花粉胚珠比、OCI指数和套袋实验结实率,探究其传粉等生殖过程对牛耳朵的广布是否有正面影响。结果表明:牛耳朵的自然花期是3—5月,全花期约45 d,其中盛花期约20 d,单花期6～8 d;开花后1～2 d花粉活力最强,开花前柱头没有可授性;花粉胚珠比为537;杂交指数为5;去雌套袋、去雄套袋均无法结实,说明本种不存在无融合生殖;与自然授粉相比,自花授粉结实率略低,异花授粉结实率略高,说明自交亲和;牛耳朵的主要传粉者是花条蜂(Anthophora florea)和熊蜂(Bombus sp.)。花蜜产量较高、花粉量较大、花粉活力较强等特点,有利于牛耳朵完成传粉和结实的整个繁殖过程。因此,这一结果显然有利于牛耳朵的拓殖进而广布在我国华南至西南地区的喀斯特地区。     

Strength and variability of postmating reproductive isolating barriers between four European white oak species

The identification and quantification of the relative importance of reproductive isolating barriers is of fundamental importance to understand species maintenance in the face of interspecific gene flow between hybridising species. Yet, such assessments require extensive experimental fertilisations that are particularly difficult when dealing with more than two hybridising and long-generation-time species such as oaks. Here, we quantify the relative contribution of four postmating reproductive isolating barriers consisting of two prezygotic barriers (gametic incompatibility, conspecific pollen precedence) and two postzygotic barriers (germination rate, early survival) from extensively controlled pollinations between four oak species (Quercus robur, Quercus petraea, Quercus pubescens and Quercus pyrenaica) that have been shown to frequently hybridise in natural populations. We found high variation in the strength of total reproductive isolation between species, ranging from total reproductive isolation to advantage toward hybrid formation. As previously found, Q. robur pollen was unable to fertilise Q. petraea due to a strong reproductive isolating mechanism. On the contrary, Q. pubescens pollen was more efficient at fertilising Q. petraea than conspecific pollen. Overall, prezygotic barriers contribute far more than postzygotic barriers to isolate species reproductively, suggesting a role for reinforcement in the development of prezygotic barriers. Conspecific pollen precedence reduced hybrid formation when pollen competition was allowed; however, presence of conspecific pollen did not totally prevent hybridization. Our results suggest that pollen competition depends on multiple ecological and environmental parameters, including species local abundance, and that it may be of uppermost importance to understand interspecific gene flow among natural multispecies populations.