外生菌根真菌多样性的分布格局与维持机制研究进展

外生菌根(ectomycorrhiza,ECM)是由土壤真菌与陆地植物根系形成的一种互惠共生体。ECM真菌从寄主植物中获取生长所需的碳源,同时促进寄主吸收氮、磷等矿物营养物质和水分。作为生态系统的重要组分,ECM真菌在生态系统的演替和多样性维持中发挥着重要的作用,因而揭示ECM真菌多样性的分布格局与维持机制是生物多样性与生态系统功能研究的热点领域之一。本文对ECM真菌多样性的最新研究进展进行了综合分析,相关研究显示,从热带到亚热带、温带森林,每种寄主植物上ECM真菌的平均物种数逐渐升高。扩散和选择过程都影响ECM真菌的分布格局,其中扩散对ECM真菌分布的影响具有空间尺度依赖性,即在全球和局域尺度上,扩散对ECM真菌分布的影响较弱,而在区域和小尺度上很强。同时,在局域尺度上,扩散对ECM真菌的分布具有寄主植物优势度依赖性,即在寄主植物不占优势的生态系统中,扩散对ECM真菌的分布有明显作用;而在寄主植物占优势的生态系统中则无影响。植物、动物、微生物和非生物因素的选择也都影响ECM真菌的分布格局,其中在温带地区所有研究均表明选择对ECM真菌的分布有影响,但是在热带地区有的研究表明选择对ECM真菌的分布有影响,而有的研究则显示无影响。植物的多样性和生产力都能影响ECM真菌的多样性,其中在温带、亚热带和热带森林中寄主植物属的多样性决定ECM真菌多样性,而植物生产力多样性假说只在一些温带的研究中得到证实。未来的研究重点应关注全球尺度,特别是在全球气候变化背景下的ECM真菌多样性的分布格局、维持机制及其生态系统功能等方面。     

丛枝菌根真菌形态结构、物种多样性和群落组成对氮沉降响应研究进展

工业革命以来,人类活动输入到生态系统中的氮迅速增加,已突破地球所能承受的氮循环阈值。过量氮沉降会造成生物多样性丧失等一系列危害,严重影响生态系统结构和功能。丛枝菌根(AM)真菌能够与大约70%-80%的陆地植物种类形成共生关系,在宿主植物养分吸收、抵抗外界不良环境压力、群落动态和物种共存、生物地球化学循环等方面具有重要的作用。探究AM真菌对氮沉降的响应对认识和把握菌根真菌缓解氮沉降的负面后果,维持生态系统的结构和功能具有重要意义。本文综述了AM真菌的形态结构、物种多样性和群落组成等对氮沉降的响应机制。前人研究表明氮沉降通常降低AM真菌的根系定殖率,减少根外菌丝密度和土壤孢子密度,改变菌丝生长的时间动态;降低AM真菌多样性,改变AM真菌群落组成。氮沉降主要通过缓解植物氮限制、降低植物对菌根的依赖性、减少植物对菌根的碳分配、改变根系和土壤中菌根生物量比率、在植物根内维持稳定的菌根真菌组成作为应对未来扰动的“保险”、改变土壤资源有效性及土壤酸度等直接和间接途径影响AM真菌结构和功能。我们建议在未来研究中整合多组学手段、开展学科交叉,聚焦复杂的生物互作体系对氮沉降的响应机制,以及AM真菌对氮沉降响应的生态后果。     

病原菌及菌根菌维持森林植物多样性机制的研究进展

森林植物物种与土壤微生物之间的相互作用决定森林生物多样性。尤其是土壤中的病原菌、菌根菌等微生物在森林物种多样性保护中起到重要作用。Janzen-Connell假说和植物-土壤反馈模型是利用植物与土壤微生物之间的相互作用关系解释森林物种多样性机制的重要模型。本文针对土壤真菌解释森林物种多样性机制进行了综合评述，介绍了病原菌和菌根菌各自在森林实生苗更新的作用机制，探讨病原菌及其菌根菌两者对森林物种多样性的相对重要性，森林实生苗与土壤微生物之间相互作用的变化规律，总结了近年来国际森林物种多样性机制的研究。提出了病原菌和菌根菌两者共同在生态系统中的作用，并探讨未来的研究方向。     

丛枝菌根共生关系的信号机制研究进展

在植物与微生物的共生体中,最广泛的互惠共生体就是丛枝菌根.真菌在植物根系形成菌根后,菌丝通过根的皮层细胞获取植物提供的碳源,同时将矿物营养和水从土壤转运到皮层细胞,这种共生过程的研究在生物多样性的保护、陆生植物的起源与演化、退化生态系统的修复与重建以及农业、林业和园艺业的应用具有重要的意义.近年来丛枝菌根真菌与植物根系建立共生关系的信号传导途径和作用机制备受关注,也取得了突破性的进展.本文对丛枝菌根真菌与植物根系在共生关系形成、营养交换以及防御方面的分子信号和细胞方面的研究进展进行综述,并对发展前景作以展望.     

外生菌根真菌与内生细菌共生互作的研究进展

外生菌根真菌能与很多高等植物共生,广泛存在于自然界,在促进植物生长和养分吸收、增强宿主抗逆性及维持森林生态系统稳定等方面发挥着重要作用。除与寄主植物密切联系外,外生菌根真菌,在其生命周期中与细菌群落进行物理和代谢相互作用常形成共生关系。这些细菌对外生菌根真菌菌丝生长、生物量增加及子实体的形成具有积极影响。本文阐述了外生菌根真菌与内生细菌共生现象的发现、共生关系的建立、内生细菌促进外生菌根真菌生长和发育及宿主与微生物组的研究方法等,以期更好地巩固外生菌根真菌的生物学及生态学等基础性知识,并利用细菌与真菌的相互作用为可食用外生菌根真菌的生物防治、菌肥研究、人工驯化及栽培提供思路。     

RNA-Seq在AM真菌研究中的应用

丛枝菌根(arbuscular mycorrhizas,AM)真菌是农业生态系统中重要的微生物成员之一,可与约80%的维管束植物建立共生关系,这种共生关系一直伴随植物的进化过程,是影响植物生长及多样性的关键因素。转录组测序技术已广泛用于植物-AM真菌共生互作中信号传导、代谢、蛋白合成等生物过程的分子机理的研究。本文归纳了AM真菌与植物共生过程中参与植物胁迫防御、蛋白合成、蛋白折叠和降解、能量代谢、信号转导、转录等相关功能基因研究进展,如磷酸盐转运蛋白、凝集素前体、谷胱甘肽硫-转移酶、Mtha1质膜ATP酶、核糖体蛋白等相关基因,总结了相关研究中基因功能特征。为进一步深入研究AM真菌与植物共生机制提供理论依据。     

兰科植物内生细菌物种多样性及其促生机理研究进展

内生细菌影响兰科植物菌根形成和共生关系的稳定性,在兰科植物的生活史中起着重要作用。内生细菌通过分泌植物激素、采用光合作用、生物固氮或促进矿质营养的循环以及产生铁载体、合成其他活性物质等途径来促进兰科植物生长发育。综述了兰科植物内生细菌物种多样性的研究方法及其对兰科植物的促生机理,基于兰科植物与共生微生物的密切关系,认为内生细菌间、内生细菌与兰科植物菌根真菌间的互作是揭示兰科植物与内生细菌互作机理的重要方向。     

中国AM真菌的生物多样性

菌根是真菌与植物根系所建立的互惠共生体 ,其中以丛枝菌根在自然界中分布最广。AM真菌遍布各生态系统 ,不仅大量分布于农田和森林土壤 ,而且还广泛存在于多种逆境环境中。绝大多数的植物包括苔鲜、蕨类、裸子植物、被子植物都能被AM真菌侵染。我国的AM真菌研究始于 2 0世纪 80年代 ,迄今为止 ,已经对多种生态环境中多种寄主植物根围的AM真菌进行了调查研究 ,共报道了 7个属的 99种AM真菌。本文从物种多样性、生境多样性和寄主多样性等三个方面概括介绍了 2 0年来我国在AM真菌生物多样性研究中取得的进展 ,并探讨了未来的研究动向。     

菌根真菌是唱响生物共生交响曲的主角——菌根真菌专辑序言

地球上任何生物都不是单独进行生命活动和进化的,即生物之间更多的是依靠密切联合、共生互助、需求互补和共同发展。其中,陆地生态系统中的强大分解者真菌和强大生产者植物关系密切,特别是以菌根真菌(mycorrhizal fungi)为代表的植物共生真菌自始至终与植物共生,这一强-强共生联合在维持生态平衡、保存生态系统可持续生产力与生态系统综合服务功能体系中,其分布之广、作用之多、功能之强和贡献之大,可谓名副其实的生物共生体系中的主导者。近年来,中国在真菌与植物共生研究领域成绩斐然,占据世界重要地位。本期《菌物学报》"菌根真菌专刊"刊登了2篇综述和20篇研究报告。综述分别对丛枝菌根(AM)真菌在煤矿区生态修复应用研究和兰科植物与菌根真菌的营养关系进行了总结和热点论述;研究报告分别对菌物界球囊菌门AM真菌全球公认种的中文学名给予了全面规范正确的描述、对中国部分林区红桦外生菌根真菌多样性、华山松印度块菌菌根中的块菌交配型基因、AM真菌对枳吸收磷和分泌磷酸酶的影响、转Bt基因棉叶片腐熟物抑制AM真菌定殖及菌根对磷的吸收、低pH影响AM真菌丛枝发育和磷的吸收、接种AM真菌与间作对红壤上玉米和大豆种间氮素竞争的影响、AM真菌及其菌种组合对植物根结线虫病害的影响以及接种AM真菌和施加铁可协同降低水稻砷累积等方面进行了研究。本期内容基本体现了中国菌根真菌分类、物种多样性、生理学、生态学、生理生态效应与作用机制研究的最新进展,对当前和今后开展植物共生真菌的研究具有重要的引领作用。     

菌根真菌在陆地生态系统碳循环中的作用

在陆地生态系统中,土壤、植被与大气之间有着可观的碳交换通量,陆地生态系统碳循环也和全球气候变化密切关联。菌根真菌可与绝大多数陆地植物建立菌根共生关系,通过矿质养分-碳交换连接起生态系统地上与地下部分,深度参与和影响陆地生态系统的碳循环过程。该文从碳的输入,土壤有机质的形成、稳定和分解等4个关键环节分别论述了菌根真菌在陆地生态系统碳循环中的作用。研究表明,菌根真菌在陆地生态系统碳的输入过程中扮演关键角色,其通过改善植物矿质营养,参与植物逆境响应,影响植物的光合作用强度,以及调控植物多样性与生产力之间的关系等多种途径,维持或提高植被初级生产力;大气中的CO₂被植物固定后,一部分碳经由菌丝网络输送到土壤中,随后经微生物的分解和转化,与矿物结合或被团聚体包裹而被稳定在土壤中;同时,菌根真菌通过影响根际激发效应和菌丝际生物化学过程,如分泌特定胞外酶,与菌丝际微生物互作,驱动芬顿反应,以及与腐生微生物竞争等,调控土壤有机质的分解和转化过程。考虑到菌根真菌对环境和气候变化的敏感性,该文还探讨了全球变化因子对菌根真菌介导的碳循环过程的影响。最后,该文对未来研究方向进行了展望,并提...     

Plant hormones as signals in arbuscular mycorrhizal symbiosis

Abstract

Arbuscular mycorrhizal (AM) fungi are non-specific symbionts developing mutual and beneficial symbiosis with most terrestrial plants. Because of the obligatory nature of the symbiosis, the presence of the host plant during the onset and proceeding of symbiosis is necessary. However, AM fungal spores are able to germinate in the absence of the host plant. The fungi detect the presence of the host plant through some signal communications. Among the signal molecules, which can affect mycorrhizal symbiosis are plant hormones, which may positively or adversely affect the symbiosis. In this review article, some of the most recent findings regarding the signaling effects of plant hormones, on mycorrhizal fungal symbiosis are reviewed. This may be useful for the production of plants, which are more responsive to mycorrhizal symbiosis under stress.     

Mycorrhizas: Gene to Function

Substantial progress has been made toward development of molecular tools for identification and quantification of mycorrhizal fungi in roots and evaluation of the diversity of ectomycorrhizal (ECM) fungi and the phylogeny and genetic structure of arbuscular mycorrhizal (AM) fungi. rDNA analysis confirms high diversity of ECM fungi on their hosts, and for AM fungi has revealed considerable genetic variation within and among morphologically similar AM fungal species. The fungal and plant genes, regulation of their expression, and biochemical pathways for nutrient exchange between symbiotic partners are now coming under intense study and will eventually be used to define the ecological nutritional role of the fungi. While molecular biological approaches have increased understanding of the mycorrhizal symbiosis, such knowledge about these lower-scale processes has yet to influence our understanding of larger-scale responses to any great extent.     

Fungal‐host diversity among mycoheterotrophic plants increases proportionally to their fungal‐host overlap

The vast majority of plants obtain an important proportion of vital resources from soil through mycorrhizal fungi. Generally, this happens in exchange of photosynthetically fixed carbon, but occasionally the interaction is mycoheterotrophic, and plants obtain carbon from mycorrhizal fungi. This process results in an antagonistic interaction between mycoheterotrophic plants and their fungal hosts. Importantly, the fungal‐host diversity available for plants is restricted as mycoheterotrophic interactions often involve narrow lineages of fungal hosts. Unfortunately, little is known whether fungal‐host diversity may be additionally modulated by plant–plant interactions through shared hosts. Yet, this may have important implications for plant competition and coexistence. Here, we use DNA sequencing data to investigate the interaction patterns between mycoheterotrophic plants and arbuscular mycorrhizal fungi. We find no phylogenetic signal on the number of fungal hosts nor on the fungal hosts shared among mycoheterotrophic plants. However, we observe a potential trend toward increased phylogenetic diversity of fungal hosts among mycoheterotrophic plants with increasing overlap in their fungal hosts. While these patterns remain for groups of plants regardless of location, we do find higher levels of overlap and diversity among plants from the same location. These findings suggest that species coexistence cannot be fully understood without attention to the two sides of ecological interactions.     

Links between tree species, symbiotic fungal diversity and ecosystem functioning in simplified tropical ecosystems

We studied the relationships among plant and arbuscular mycorrhizal (AM) fungal diversity, and their effects on ecosystem function, in a series of replicate tropical forestry plots in the La Selva Biological Station, Costa Rica. Forestry plots were 12 yr old and were either monocultures of three tree species, or polycultures of the tree species with two additional understory species. Relationships among the AM fungal spore community, host species, plant community diversity and ecosystem phosphorus-use efficiency (PUE) and net primary productivity (NPP) were assessed. Analysis of the relative abundance of AM fungal spores found that host tree species had a significant effect on the AM fungal community, as did host plant community diversity (monocultures vs polycultures). The Shannon diversity index of the AM fungal spore community differed significantly among the three host tree species, but was not significantly different between monoculture and polyculture plots. Over all the plots, significant positive relationships were found between AM fungal diversity and ecosystem NPP, and between AM fungal community evenness and PUE. Relative abundance of two of the dominant AM fungal species also showed significant correlations with NPP and PUE. We conclude that the AM fungal community composition in tropical forests is sensitive to host species, and provide evidence supporting the hypothesis that the diversity of AM fungi in tropical forests and ecosystem NPP covaries.     

菌根真菌与植物共生营养交换机制研究进展

菌根是陆地生态系统普遍存在的、由土壤中的菌根真菌侵染宿主植物根系形成的联合共生体.菌根的建立是以共生体双方的营养交换为基础的:菌根真菌从土壤中吸收氮、磷等营养物质并转运给宿主植物,供其生长;作为交换,植物则以脂质或糖的形式向菌根真菌提供其生长所必需的碳水化合物.近年来,菌根真菌与宿主植物间的营养交换机制一直是研究的热点,国内外对菌根真菌介导的植物营养物质吸收和转运机制的研究也取得了巨大进展.本文综述了丛枝和外生两种菌根真菌与宿主植物间营养交换的最新研究进展,尤其是碳、氮、磷等几种重要营养物质的吸收与双向转运机制,以及营养交换在菌根形成中的潜在调控作用,并对目前存在的关键问题和未来研究方向进行了分析和展望,这对菌根模型的建立及菌根效益的优化具有重要意义.     

Mycorrhizal symbiosis increases the benefits of plant facilitative interactions

The diversity of pathways through which mycorrhizal fungi alter plant coexistence hinders the understanding of their effects on plant‐plant interactions. The outcome of plant facilitative interactions can be indirectly affected by mycorrhizal symbiosis, ultimately shaping biodiversity patterns. We tested whether mycorrhizal symbiosis enhances plant facilitative interactions and whether its effect is consistent across different methodological approaches and biological scenarios. We conducted a meta‐analysis of 215 cases (involving 21 nurse and 29 facilitated species), in which the performance of a facilitated plant species is measured in the presence or absence of mycorrhizal fungi. We show that mycorrhizal fungi significantly enhance plant facilitative interactions mainly through an increment in plant biomass (aboveground) and nutrient content, although their effects differ across biological contexts. In semiarid environments mycorrhizal symbiosis enhances plant facilitation, while its effect is non‐significant in temperate ecosystems. In addition, arbuscular but not ecto‐mycorrhizal (EMF) fungi significantly enhance plant facilitation, particularly increasing the P content of the plants more than EMF. Some knowledge gaps regarding the importance of this phenomenon have been detected in this meta‐analysis. The effect of mycorrhizal symbiosis on plant facilitation has rarely been assessed in other ecosystems different from semiarid and temperate forests, and rarely considering other fungal benefits provided to plants besides nutrients. Finally, we are still far from understanding the effects of the whole fungal community on plant‐plant interactions, and on plant species coexistence.     

Programming good relations--development of the arbuscular mycorrhizal symbiosis

The majority of plants live in symbiotic associations with fungi or bacteria that improve their nutrition. Critical steps in a symbiosis are mutual recognition and subsequently the establishment of an intimate association, which involves the penetration of plant tissues and, in many cases, the invasion of individual host cells by the microbial symbiont. Recent advances revealed that in the arbuscular mycorrhizal symbiosis with soil fungi of the order Glomeromycota, plant-derived signals attract fungal hyphae and stimulate their growth. Upon physical attachment of the fungal symbiont to the root surface, an active plant developmental program prepares the epidermal cells for penetration by the fungus. Thus, plants actively help symbiotic fungi to colonize their roots rather than just tolerating them.     

Specificity of assemblage,not fungal partner species,explains mycorrhizal partnerships of mycoheterotrophic Burmannia plants

Mycoheterotrophic plants (MHPs) growing on arbuscular mycorrhizal fungi (AMF) usually maintain specialized mycorrhizal associations. The level of specificity varies between MHPs, although it remains largely unknown whether interactions with mycorrhizal fungi differ by plant lineage, species, and/or by population. Here, we investigate the mycorrhizal interactions among Burmannia species (Burmanniaceae) with different trophic modes using high-throughput DNA sequencing. We characterized the inter- and intraspecific dynamics of the fungal communities by assessing the composition and diversity of fungi among sites. We found that fully mycoheterotrophic species are more specialized in their fungal associations than chlorophyllous species, and that this specialization possibly results from the gradual loss of some fungal groups. In particular, although many fungal species were shared by different Burmannia species, fully MHP species typically host species-specific fungal assemblages, suggesting that they have a preference for the selected fungi. Although no apparent cophylogenetic relationship was detected between fungi and plants, we observe that evolutionarily closely related plants tend to have a greater proportion of shared or closely related fungal partners. Our findings suggest a host preference and specialization toward fungal assemblages in Burmannia, improving understanding of interactions between MHPs and fungi.Subject terms: Fungi, Plant sciences, Evolution     

How are plant and fungal communities linked to each other in belowground ecosystems? A massively parallel pyrosequencing analysis of the association specificity of root-associated fungi and their host plants

In natural forests, hundreds of fungal species colonize plant roots. The preference or specificity for partners in these symbiotic relationships is a key to understanding how the community structures of root‐associated fungi and their host plants influence each other. In an oak‐dominated forest in Japan, we investigated the root‐associated fungal community based on a pyrosequencing analysis of the roots of 33 plant species. Of the 387 fungal taxa observed, 153 (39.5%) were identified on at least two plant species. Although many mycorrhizal and root‐endophytic fungi are shared between the plant species, the five most common plant species in the community had specificity in their association with fungal taxa. Likewise, fungi displayed remarkable variation in their association specificity for plants even within the same phylogenetic or ecological groups. For example, some fungi in the ectomycorrhizal family Russulaceae were detected almost exclusively on specific oak (Quercus) species, whereas other Russulaceae fungi were found even on “non‐ectomycorrhizal” plants (e.g., Lyonia and Ilex). Putatively endophytic ascomycetes in the orders Helotiales and Chaetothyriales also displayed variation in their association specificity and many of them were shared among plant species as major symbionts. These results suggest that the entire structure of belowground plant–fungal associations is described neither by the random sharing of hosts/symbionts nor by complete compartmentalization by mycorrhizal type. Rather, the colonization of multiple types of mycorrhizal fungi on the same plant species and the prevalence of diverse root‐endophytic fungi may be important features of belowground linkage between plant and fungal communities.