兰科菌根的生态学研究进展

兰科植物(Orchidaceae)是典型的菌根植物,自然条件下其种子的成功萌发和生长的早期阶段对菌根真菌有绝对的依赖性,在有些成年兰科植物中菌根真菌仍起着重要的作用。目前大部分兰科植物已为濒危物种,鉴于兰科植物天然的菌根共生关系,开展兰科植物和菌根真菌互作的生态学研究不仅具有极高的科研价值,更有助于兰科植物的物种保护和野生种群的生态恢复。近年研究表明,兰科植物对真菌的选择和二者共生关系的建立与菌根真菌的空间分布和丰度密切相关,然而当前对自然环境中兰科菌根真菌的实际分布还了解甚少,因此文章从生态学角度系统分析兰科植物与菌根真菌的关系,探讨该领域的研究热点,旨在为兰科菌根的生态学研究提供参考。     

辽宁省八种兰科植物根内生真菌多样性

兰科植物的生存强烈依赖菌根真菌,研究兰科菌根真菌对兰科植物的保护有重要作用。本研究以辽宁省的无柱兰(Amitostigma gracile)、二叶舌唇兰(Platanthera chlorantha)、小斑叶兰(Goodyera repens)、蜻蜓兰(Tulotis fuscescens)、山兰(Oreorchis patens)、羊耳蒜(Liparis japonica)、长苞头蕊兰(Cephalanthera longibracteata)和绶草(Spiranthes sinensis) 8种属于极小种群的野生兰科植物为例,利用第二代测序技术对其根内生真菌多样性进行了研究。结果表明:无柱兰、二叶舌唇兰、小斑叶兰和山兰都偏好与角担菌科(Ceratobasidiaceae)真菌共生,羊耳蒜偏好与胶膜菌科(Tulasnellaceae)真菌共生;长苞头蕊兰主要与革菌科(Thelephoraceae)和蜡壳耳科(Sebacinaceae)真菌共生;绶草不仅能与丝核菌属(Rhizoctonia)真菌共生,还能与蜡壳耳科真菌共生;同种兰科植物的不同植株在同一生境下所选择的菌根真菌有差异,而同一地点的不同兰科植物的菌根真菌群落各不相同。由此可见,兰科植物根中菌根真菌的组成并非完全受植物自身控制,但主要菌根真菌仍取决于兰科植物的选择;这8种兰科植物根中的真菌绝大多数为非菌根真菌,而菌根真菌的丰度通常很低,这可能是辽宁地区兰科植物稀少的原因之一。     

鼓槌石斛的地理分布与菌根真菌区系组成的相关性

本文研究了兰科石斛属鼓槌石斛的地理分布与菌根真菌区系组成的相关性。采用克隆文库技术对云南省西双版纳和临沧市两个地区的8份野生鼓槌石斛根部样品进行了分析。结果表明,共从两个地区的鼓槌石斛根部获得了14个真菌的可操作分类单元（OTU）,主要隶属于胶膜菌科Tulasnellaceae和小纺锤菌目Atractiellales。分析鼓槌石斛对菌根真菌的专一性和偏好性发现,鼓槌石斛对菌根真菌专一性较低,每个植株都能同时与多种菌根真菌共生;不同地理分布的鼓槌石斛菌根真菌类群存在明显差异,两个地区的鼓槌石斛的菌根真菌中只有1个OTU是相同的,其余均不同。说明菌根真菌可能和鼓槌石斛的生态适应存在一定的相关性。     

春兰和蕙兰菌根真菌rDNA ITS序列及共生专一性分析

春兰(Cymbidium goeringii)和蕙兰(Cymbidium faberi)是我国较为广泛分布的地生类型兰属植物,具有悠久的栽培历史和很高的经济价值.菌根真菌与兰科植物专一性关系一直是兰科茵根研究中的热点.该文对35株分离自浙江天目山野生春兰和蕙兰的菌根真菌进行了rDNA ITS序列分析,并在此基础上初步探讨了菌根真菌与春兰、蕙兰之间的专一性关系.结果表明,分离获得的菌根真菌与其共生兰属植物在种的层面具显著专一性,即物种是影响或决定浙江天目山地区春兰、蕙兰与共生菌根真菌专一性的重要因素;研究同时发现,自蕙兰同一条根分离获得的菌根真菌菌株间亦表现丰富的多样性差异.     

兰科植物菌根真菌研究新见解

兰科(Orchidaceae)在地球生命系统演化中占有十分重要的地位,几乎全部兰科植物均处于不同程度的濒危状态,研究兰科菌根真菌对于保护珍稀濒危兰科植物具有重要意义。该文在对菌根真菌相关的概念及研究方法进行综述的基础上,对兰科菌根真菌的主要类群、特异性及其与兰科植物稀有性之间的关系,以及兰科菌根真菌与兰科植物之间的营养关系和进化关系进行了总结。兰科菌根真菌的研究方法可以归纳为经典研究方法、早期分子生物学方法、rDNA片段高通量测序法、宏基因组学方法。兰科菌根真菌类群主要隶属于担子菌门(Basidiomycota)、子囊菌门(Ascomycota)和毛霉门(Mucoromycota)。根据兰科菌根真菌特异性与否,首次明确了兰科菌根真菌定植关系可分为三大类:特异性定植、广泛性定植和特异-广泛兼性定植。根据营养关系特点,首次将兰科植物与菌根真菌之间的营养关系划分为三大类:兰花单向利好型、典型共生型、分工合作型。兰科菌根真菌特异性与兰科植物稀有性之间的关系呈现出两面性,而兰科菌根真菌与兰科植物之间是否存在协同进化关系还需要更多的研究才能阐明。此外,该文还对兰科菌根真菌领域今后的研究提出了一些思路。     

辽宁省9种兰科植物根内与根际土壤中真菌群落结构的差异

兰科植物的生存及生长高度依赖其根中的共生真菌, 其中的菌根真菌更是对兰科植物的种子萌发与后续生长有着非常重要的作用, 研究兰科植物根中的真菌, 尤其是菌根真菌, 对兰科植物的保护有重要作用。该研究利用第二代测序技术, 对中国辽宁省境内的9种属于极小种群的兰科植物的根、根际土和根围土中的真菌群落和菌根真菌组成进行了研究。结果显示, 兰科植物根中的真菌群落和根际土、根围土中的真菌群落具有显著差异。兰科植物根中的总操作分类单元(OTU)数目远小于根际土和根围土中的总OTU数目。同时, 兰科植物根中菌根真菌的种类和丰度与根际土、根围土中菌根真菌的种类与丰度没有明显联系。FunGuild分析结果显示, 丛枝菌根真菌在根际土与根围土中的丰度非常高, 但在兰科植物的根中却数量极少。这些结果表明, 兰科植物根中的真菌群落与土壤中的真菌群落在一定程度上是相互独立的。     

辽宁省9种兰科植物根内与根际土壤中真菌群落结构的差异

兰科植物的生存及生长高度依赖其根中的共生真菌,其中的菌根真菌更是对兰科植物的种子萌发与后续生长有着非常重要的作用,研究兰科植物根中的真菌,尤其是菌根真菌,对兰科植物的保护有重要作用。该研究利用第二代测序技术,对中国辽宁省境内的9种属于极小种群的兰科植物的根、根际土和根围土中的真菌群落和菌根真菌组成进行了研究。结果显示,兰科植物根中的真菌群落和根际土、根围土中的真菌群落具有显著差异。兰科植物根中的总操作分类单元(OTU)数目远小于根际土和根围土中的总OTU数目。同时,兰科植物根中菌根真菌的种类和丰度与根际土、根围土中菌根真菌的种类与丰度没有明显联系。FunGuild分析结果显示,丛枝菌根真菌在根际土与根围土中的丰度非常高,但在兰科植物的根中却数量极少。这些结果表明,兰科植物根中的真菌群落与土壤中的真菌群落在一定程度上是相互独立的。     

独花兰菌根真菌的分离及rDNA ITS序列在其分类鉴定中的应用

独花兰(Changnienia amoena Chien)为我国特有的独属独种兰科植物,仅生长于长江中下游及陕西南部的山地林下及沟谷中,是中国特有兰科物种之一,被列为国家二级保护植物.以浙江天目山自然保护区的野生独花兰中分离获得的菌根真菌为对象,应用传统的形态结构鉴别与rDNA ITS分子生物学手段相结合的研究方法,进行了菌株的分类鉴定研究,确定该菌株为兰科菌根真菌之一的胶膜菌属(Tulasnella)真菌.研究结果对于全面了解兰科植物菌根真菌的特征和有效保护独花兰植物资源均具较大意义和参考价值.     

菌根真菌与兰科植物互作的组学研究进展

兰科植物因其具有丰富的物种多样性和重要的社会经济价值,多年来一直是植物学及生态学界的重点研究对象。菌根真菌对兰科植物的种子萌发、营养吸收和种群动态等多个方面都具有十分重要的作用,因而近年来受到越来越多的关注。探究菌根真菌与兰科植物互作的内在机制是目前兰科菌根研究的一大热点领域,同时也为兰科植物野生资源保护和种群恢复提供了许多新方法与新思路。随着新一代测序技术以及多种组学数据库的发展与建立,菌根真菌与兰科植物互作机制研究已然进入了一个全新的时代。纵观近年来的研究,通过基因组学、转录组学、蛋白质组学和代谢组学等相关技术,人们对兰科菌根共生过程中的种子萌发、营养物质转运、信号转导、宿主免疫和逆境抗性等方面的内在机制有了一定的了解。本文对近十年来国内外采用组学技术研究菌根真菌与兰科植物互作机制方面的研究成果进行了总结和梳理,并对未来该领域的研究进行了展望。     

兰科植物与菌根真菌的营养关系

兰科植物与真菌具有天然的菌根共生关系。兰科植物种子细小,无胚乳,自然条件下只有与适宜的真菌共生才能萌发;兰科植物作为有花植物中最大的科之一,有光合自养、混合营养及完全真菌异养等营养类型。近年研究表明,不同营养类型的兰科植物其菌根真菌常具有一定的差异性,表现出不同的营养作用关系。本文对不同营养类型兰科植物与菌根真菌的营养作用关系的研究进展进行综述,并对兰科植物菌根营养机理、营养关系的变化等进行讨论,以期为兰科菌根营养学研究及菌根技术应用于兰科植物快繁和保育工作等提供参考。     

Studies of Mycorrhizal Fungi of Chinese Orchids and Their Role in Orchid Conservation in China—A Review

China has over 1,200 species of native orchids in nearly 173 genera. About one fourth of native species are of horticultural merit. Some species are of Chinese medicinal value. In fact, the demand on orchid species with high Chinese medicinal values such as Gastrodia elata, Dendrobium offcinale, along with demands on species of cultural importance, such as those in the genus of Cymbidium, is a major factor causing wild populations to diminish and in some cases, drive wild populations to the brink of extinction. These market demands have also driven studies on the role of mycorrhizal fungi in orchid seed germination, seedling and adult growth, and reproduction. Most of these mycorrhizal studies of Chinese orchids, however, are published in Chinese, some in medical journals, and thus overlooked by the mainstream orchid mycorrhizal publications. Yet some of these studies contained interesting discoveries on the nature of the mycorrhizal relationships between orchids and fungi. We present a review of some of these neglected publications. The most important discovery comes from the mycorrhizal studies on G. elata, in which the researchers concluded that those fungi species required to stimulate seed germination are different from those that facilitate the growth of G. elata beyond seedling stages. In addition, presence of the mycorrhizal fungi associated with vegetative growth of post-seedling G. elata hindered the germination of seeds. These phenomena were unreported prior to these studies. Furthermore, orchid mycorrhizal studies in China differ from the mainstream orchid studies in that many epiphytic species (in the genus of Dendrobium, as medicinal herbs) were investigated as well as terrestrial orchids (mostly in the genus Cymbidium, as traditional horticultural species). The different responses between epiphytic and terrestrial orchid seeds to fungi derived from roots suggest that epiphytic orchids may have a more general mycorrhizal relationship with fungi than do terrestrial orchid species during the seed germination stage. To date, orchid mycorrhizal research in China has had a strongly commercial purpose. We suggest that this continuing research on orchid mycorrhizal relationships are a solid foundation for further research that includes more rare and endangered taxa, and more in-situ studies to assist conservation and restoration of the endangered orchids. Knowledge on the identities and roles of mycorrhizal fungi of orchids holds one of the keys to successful restoration and sustainable use of Chinese orchids.     

Specificity and preference of mycorrhizal associations in two species of the genus Dendrobium (Orchidaceae)

Dendrobium is a large genus of tropical epiphytic orchids. Some members of this genus are in danger of extinction across China. To investigate orchid mycorrhizal associations of the genus Dendrobium, plants from two Dendrobium species (Dendrobium officinale and Dendrobium fimbriatum) were collected from two habitats in Guangxi Province, China, and clone libraries were constructed to identify the mycorrhizal fungi of individual plants. A low and high degree of specificity was observed in D. officinale and D. fimbriatum, respectively. Phylogenetic analysis revealed that the majority of Dendrobium mycorrhizal fungi are members of the Tulasnellaceae, but, in some plants, members of the Ceratobasidiaceae and Pluteaceae were also found. In D. officinale, individual plants associated with more than three fungi simultaneously, and, in some cases, associations with five fungi at the same time. One fungus was shared by individual plants of D. officinale collected from the two habitats. In D. fimbriatum, only one fungal partner was found in each population, and this fungus differed between populations. The two species of Dendrobium sampled from the same habitat did not share any fungal taxa. These results provide valuable information for conservation of these orchid species.     

Relationships between orchid and fungal biodiversity: Mycorrhizal preferences in Mediterranean orchids

Orchidaceae is one of the most species-rich angiosperm families, and all orchids are fully dependent on fungi for their seed germination and their life cycle. The level of specificity of the association between orchid species and fungi can be related to the number of co-occurring orchid species. To investigate orchid mycorrhizal associations in adult-photosynthetic orchids, 16 Mediterranean orchid species belonging to 4 genera (Anacamptis, Ophrys, Orchis, and Serapias) at 11 different sites were subjected to DNA-based analysis. Eighteen operational taxonomic units representing two fungal families, Tulasnellaceae and Ceratobasidiaceae, were identified. All examined orchid species associated with different mycorrhizal fungi. Interestingly, there was a positive correlation between number of orchid species and number of mycorrhizal. Monospecific populations showed a lower number of fungi, while sympatric populations had a higher number of mycorrhizal fungi. Our results showed that Mediterranean orchid species associated with a higher number of mycorrhizal fungi confirming as photosynthetic orchids are typically generalists toward mycorrhizal fungi. Thus, photosynthetic orchids exhibit low specificity for fungal symbionts showing the potential for opportunistic associations with diverse fungi reducing competition for nutrient. We suggest that these characteristics could confer symbiotic assurance particularly in habitat with resource limitations or prone to stressful conditions.     

Endophytic fungi assemblages from 10 <Emphasis Type="Italic">Dendrobium</Emphasis> medicinal plants (Orchidaceae)

Dendrobium is the largest genus of tropical epiphytic orchid, some of which are traditional Chinese medicinal plants. The therapeutic components varied significantly among species. Endophytic microbes (fungi) hidden in medicinal plants may play an important effect on the overall quality of herb. Investigation of fungal composition in host plants is the first step toward elucidating the relationship endophyte-therapeutic content of herbal medicine. In this study, 401 culturable fungal endophytes were isolated and identified from 10 species of medicinal Dendrobium based on morphological and molecular techniques. The results showed that endophytic fungi from Dendrobium plants exhibited high biodiversity (37 genera, about 80 species). Acremonium, Alternaria, Ampelomyces, Bionectria, Cladosporium, Colletotrichum, Fusarium, Verticillium and Xylaria were the dominant fungal endophytes. Tropical epiphytic orchids appear to vary in degree of host specificity in their endophytic fungi.     

Isolation and identification of endophytic and mycorrhizal fungi from seeds and roots of <Emphasis Type="Italic">Dendrobium</Emphasis> (Orchidaceae)

The seed germination of orchids under natural conditions requires association with mycorrhizal fungi. Dendrobium nobile and Dendrobium chrysanthum are threatened orchid species in China where they are considered medicinal plants. For conservation and application of Dendrobium using symbiosis technology, we isolated culturable endophytic and mycorrhizal fungi colonized in the protocorms and adult roots of two species plants and identified them by morphological and molecular analyses (5.8S and nrLSU). Of the 127 endophytic fungi isolated, 11 Rhizoctonia-like strains were identified as Tulasnellales (three strains from protocorms of D. nobile), Sebacinales (three strains from roots of D. nobile and two strains from protocorms of D. chrysanthum) and Cantharellales (three strains from roots of D. nobile), respectively. In addition, species of Xylaria, Fusarium, Trichoderma, Colletotrichum, Pestalotiopsis, and Phomopsis were the predominant non-mycorrhizal fungi isolated, and their probable ecological roles in the Dendrobium plants are discussed. These fungal resources will be of great importance for the large-scale cultivation of Dendrobium plants using symbiotic germination technology and for the screening of bioactive metabolites from them in the future.     

Isolation and identification of Rhizoctonia-like fungi from roots of three orchid genera, Paphiopedilum, Dendrobium, and Cymbidium, collected in Chiang Rai and Chiang Mai provinces of Thailand

Three orchid genera, Paphiopedilum, Cymbidium, and Dendrobium, are among the most heavily traded ornamental plants in Thailand. In this study, 27 isolates of Rhizoctonia-like fungi were isolated from root sections of mature orchids in the three orchid genera, collected from diverse horticultural settings in Chiang Mai and Chiang Rai provinces of Thailand. Fungal identification was done by the morphological characterization, the comparison of the internal transcribed spacer and 5.8S ribosomal DNA sequences, and the phylogenetic analysis. Epulorhiza repens was found to be the most common species found in the roots of various species of all three orchid genera, whereas Epulorhiza calendulina-like isolates were strictly found in the roots of Paphiopedilum species. We have also isolated and described an anamorph of Tulasnella irregularis, four new anamorphic species in the genus Tulasnella, and a new anamorphic species in the family Tulasnellaceae. Our study provides information on diversity of root-associated fungi of the orchid genera and at the sampling sites that were rarely addressed in the previous studies.     

Isolation and identification of mycorrhizal fungi associating with an achlorophyllous plant, Epipogium roseum (Orchidaceae)

The identity of mycorrhizal fungi associated with the achlorophyllous orchid Epipogium roseum was investigated by DNA analysis. The fungi were isolated from each coiled hypha (peloton), and the ITS region of nuclear rDNA was sequenced. Phylogenetic analysis based on the neighbor-joining method showed that all the isolates clustered with fungi belonging to Psathyrella or Coprinus in Coprinaceae. Those fungi are known as saprobes, using dead organic materials for a nutritive source. Large colonies of this orchid were frequently found around tree stumps or fallen logs. In such colonies, these decaying wood materials would be used as a large and persistent carbon source for the growth of this orchid. This is the first report of Coprinaceae as an orchid mycorrhizal fungi.     

中国石斛属(兰科)植物新资料

在西藏开展兰科植物资源调查过程中,发现了2种石斛属(金石斛组)物种,通过文献和标本的查阅之后,分别确定为麦氏金石斛(Dendrobium macraei Lindl.)和西藏金石斛(D. ritaeanum King & Pantl.),两者均为中国首次记录。其中,麦氏金石斛与流苏金石斛(D. plicatile Lindley)近似,不同之处在于前者唇瓣中裂片边缘全缘,中裂片具2条纵脊,并仅延伸至唇瓣中部,先端凹; 西藏金石斛虽然植株与狭叶金石斛[D. angustifolium (Blume)Lindl.]近似,但该种花很小,萼片和花瓣不具紫色条纹且唇瓣长达1.4 cm,侧裂片三角形,花期时容易区分。同时,该文还提供了该2种石斛属植物详细的形态特征描述以及解剖图版等资料,凭证标本保存于西藏农牧学院标本馆。该发现丰富了中国兰科植物本底资料以及潜在药用植物资源储备,对中国兰科植物的生物多样性研究和药用兰科资源的调查具有重要意义。     

Low specificity and nested subset structure characterize mycorrhizal associations in five closely related species of the genus Orchis

Most orchid species rely on mycorrhizae to complete their life cycle. Despite a growing body of literature identifying orchid mycorrhizal associations, the nature and specificity of the association between orchid species and mycorrhizal fungi remains largely an open question. Nonetheless, better insights into these obligate plant–fungus associations are indispensable for understanding the biology and conservation of orchid populations. To investigate orchid mycorrhizal associations in five species of the genus Orchis (O. anthropophora, O. mascula, O. militaris, O. purpurea, and O. simia), we developed internal transcribed spacer‐based DNA arrays from extensive clone library sequence data sets, enabling rapid and simultaneous detection of a wide range of basidiomycetous mycorrhizal fungi. A low degree of specificity was observed, with two orchid species associating with nine different fungal partners. Phylogenetic analysis revealed that the majority of Orchis mycorrhizal fungi are members of the Tulasnellaceae, but in some plants, members of the Thelephoraceae, Cortinariaceae and Ceratobasidiaceae were also found. In all species except one (O. mascula), individual plants associated with more than one fungus simultaneously, and in some cases, associations with ≥3 mycorrhizal fungi at the same time were identified. Nestedness analysis showed that orchid mycorrhizal associations were significantly nested, suggesting asymmetric specialization and a dense core of interactions created by symmetric interactions between generalist species. Our results add support to the growing literature that multiple associations may be common among orchids. Low specificity or preference for a widespread fungal symbiont may partly explain the wide distribution of the investigated species.     

Mycorrhizal status of plant species in the Chaco Serrano Woodland from central Argentina

We examined the mycorrhizal type of 128 plant species in two patches of native vegetation of the Chaco Serrano Woodland, central Argentina, the largest dry forest area in South America. Of the 128 plant species investigated (belonging to 111 genera in 53 families), 114 were colonized by arbuscular mycorrhizal fungi (AM), orchid mycorrhizal associations were present in the five terrestrial orchid species analyzed, one ectomycorrhiza was only present in Salix humboldtiana Willd., and 96 harbored a dark septate endophyte (DSE) association. Co-occurrence of AM and DSE was observed in 88 plant species. We determine morphological types of arbuscular mycorrhizal fungi (Arum, Paris, and intermediate AM structures) and report the mycorrhizal status in 106 new species, 12 of which are endemic to central Argentina and two, Aa achalensis Schltr. and Buddleja cordobensis Griseb., are declared to be vulnerable species. Root colonization in the Chaco Serrano Woodland is widespread and should be considered in revegetation programs due to the deterioration of this particular ecosystem. Considering the predominance of AM and DSE associations and the various potential benefits that these associations may bring to plant establishment, they should receive special attention in conservation and reforestation of these woodlands.