兰科是被子植物中物种数量最庞大、多样性最丰富的家族, 有736个属超过28 000个物种, 大约占被子植物数量的10% (Christenhusz & Byng, 2016)。兰科植物的种子没有胚乳, 种子萌发依赖在体内定殖的真菌提供全部营养, 形成一种异养的无叶幼苗——原球茎。完成形态建成后的兰科植物根与真菌形成“兰菌根” (OM)的共生体, 这是兰科家族共有的生物学特性。成年后, 绝大多数绿色兰科植物能够通过光合作用获取全部或部分碳营养, 但仍从菌根真菌获得可观的氮营养(Shan et al., 2021); 少数没有叶片或缺失叶绿体, 地上部分已丧失光合作用能力的兰科植物则终生依赖真菌提供全部营养(Leake, 1994), 如天麻(Gastrodia elata) (杨世林等, 2000)。
氮是植物需求量最大的一种矿质营养元素, 是各类植物组织和各种生理代谢酶的构成性元素。氮通过改变其在叶片中的分配格局影响叶片的光合作用, 并通过改变碳水化合物的库-源关系和能量消耗水平而调节碳同化物质在体内的分配(王琪和徐程扬, 2005)。兰科植物组织和器官的氮含量高; 即使是终生依赖真菌的兰科植物, 其氮含量也通常高于环境中的其他自养植物(Schweiger et al., 2018), 甚至高于同样依赖真菌生活的杜鹃花科植物(Hynson et al., 2016)。同位素分析、高通量测序等的研究表明, 兰科植物富集氮的程度主要受其真菌伙伴的影响(Kuga et al., 2014; Fochi et al., 2017a, 2017b)。本文将从兰科植物营养方式、OM真菌分类、兰科植物氮营养特征和OM的氮转移机制等4个方面综述兰科植物氮营养的研究进展, 以期加深对兰科植物与真菌互利共生关系的理解和认识, 并为利用菌根技术促进兰科植物的资源保护和人工繁育奠定理论基础。
1 兰科植物营养方式与氮获取途径
随着同位素分析技术的广泛应用, 已发现多种“自养型”绿色兰科植物体内有比例不等的真菌碳, 揭示了这些物种隐秘的真菌异养特性。Gebauer和Meyer (2003)报道, 在10种被认为是自养型的兰科植物中只有红门兰属(Orchis)的2种植物是真正自养, 其他植物均不同程度地获取了真菌碳; 与碳营养相比, 植物对真菌氮的依赖程度更高: 自养的红门兰属的O. ustulata和O. mascula分别有63%和33%-37%的氮来自真菌; 真菌碳比例占30%以上的头蕊兰属(Cephalanthera)的大花头蕊兰(C. damasonium)和火烧兰属(Epipactis)的火烧兰(E. helleborine)、E. atrorubens的真菌氮比例达到80%-100%; 真菌碳占比10%以下的7种植物中, 有5种植物的真菌氮占比在10%以上。头蕊兰属和火烧兰属等一些绿色兰科植物类群的种群中经常出现“白化”个体, 其遗传背景和菌根真菌群落结构与正常植株无差别, 但它们是完全真菌异养的, 且较正常植株有更高的氮含量和15N丰度, 表明在缺乏叶绿素的情况下, 一些自养型植物可以改变获取营养的途径, 通过真菌伙伴吸收碳和氮(Gebauer & Meyer, 2003; Selosse et al., 2004; Abadie et al., 2006; Tranchida-Lombado et al., 2010; Hynson et al., 2013)。
2 OM真菌的类型
真菌与植物根系结合形成的共生体称为菌根, 它对植物的生长和适应性有重要影响。根据结构和功能, 菌根主要划分为4种类型: 丛枝菌根(AM)、外生菌根(EcM)、OM和杜鹃菌根(ericoid mycorrhiza)。OM是兰科植物特有的一种内生菌根, 其特征是: 真菌不侵入内皮层, 可以在根皮层细胞内形成“菌丝圈”的典型结构; 衰老的菌丝圈最终被植物细胞消化并吸收。研究表明, OM共生体双方对彼此的生物约束力并不对称, 植物是共生关系中获益较多的一方(Martos et al., 2012); 部分OM真菌与兰科植物的联系不具有专一性(Veldre et al., 2013); 真菌异养型兰科植物较自养型植物有更加多样化的菌根真菌谱系(Dearnaley et al., 2012)。
兰科植物的共生真菌包括腐生真菌和少数EcM真菌类群, 腐生真菌主要来自伞菌纲(Agaricomycetes)和盘菌纲(Pezizomycetes)(Brundrett & Tedersoo, 2018)(表1)。腐生真菌中包含被称为“类丝核菌” (rhizoctonia-like)的最古老的OM真菌, 隶属胶膜菌科(Tulasnellaceae)、角担菌科(Ceratobasidiaceae)及无孢蜡壳科(Serendipitaceae)/蜡壳耳目(Sebacinales)。EcM真菌类群是新近被证实的部分无叶绿素兰科植物的共生真菌(Suetsugu et al., 2021)。此外, 还有能生活在兰科植物根系的内生真菌(Petrini, 1991), 它们不形成菌根结构, 分类上也不属于任何已知的菌根真菌类群。与AM和EcM相比, 能形成OM的真菌数量庞大, 种类繁多, 具有更复杂的生物多样性(van der Heijden et al., 2015)(表1)。兰科植物不断扩大真菌伙伴的范围, 这种转变被认为是对兰科家族进化出现真菌异养型物种的预适应(Abadie et al., 2006; Motomura et al., 2010; Dearnaley et al., 2012)。
表1 兰菌根真菌及其类型
Table 1
| 真菌类型 Fungi type | 真菌分类群 Fungi taxon | 兰科植物 Orchid | 参考文献 Reference | |||||
|---|---|---|---|---|---|---|---|---|
| 纲 Class | 目 Order | 科 Family | 属 Genus | |||||
| 类丝核菌 Rhizoctonia-like | 担子菌纲 Basidiomycetes | 胶膜菌科 Tulasnellaceae | Dactylorhiza majalis, Ophrys insectifera, Platanthera bifolia, 手参 Gymnadenia conopsea, 四裂红门兰 Orchis militaris | Schweiger et al., 2018 | ||||
| 蜡壳耳属 Sebacina | Dactylorhiza majalis, Pseudorchis albida | Stöckel et al., 2014; Schweiger et al., 2018 | ||||||
| 胶膜菌属 Tulasnella | 硬叶兜兰 Paphiopedilum micranthum, 杏黄兜兰 P. armeniacum, 长瓣兜兰 P. dianthum, 黄花杓兰 Cypripedium flavum, 紫点杓兰 C. guttatum, 西藏杓兰 C. tibeticum, 二叶舌唇兰 Platanthera chlorantha, Epipactis atrorubens, Serapias parviflora, Pseudorchis albida, Dactylorhiza majalis | Bidartondo et al., 2004; Yuan et al., 2010; Stöckel et al., 2014 | ||||||
| 角担菌科 Ceratobasidiaceae | Dactylorhiza majalis, 黄蜂兰 Ophrys insectifera, 细距舌唇兰 Platanthera bifolia, 四裂红门兰 Orchis militaris | Schweiger et al., 2018 | ||||||
| 角担菌属 Ceratobasidium | 新疆火烧兰 Epipactis palustris, 火烧兰 E. helleborine, 剑叶拟兰 Apostasia wallichii, A. nipponica, 二叶舌唇兰 Platanthera chlorantha, 头蕊兰 Cephalanthera longifolia | Bidartondo et al., 2004; Abadie et al., 2006 | ||||||
| Thanatephorus | 细距舌唇兰 Platanthera bifolia, 头蕊兰 Cephalanthera longifolia, 无叶兰 Aphyllorchis montana | Abadie et al., 2006; Roy et al., 2009a; Schweiger et al., 2018 | ||||||
| 非类丝核菌的 腐生真菌 Non rhizoctonia-like saprotrophic fungi | 子囊菌纲 Ascomycetes | 粪壳菌目 Sordariales | 头蕊兰 Cephalanthera longifolia | Abadie et al., 2006 | ||||
| 担子菌纲 Basidiomycetes | Meripilaceae | Gastrodia falcone, 肉果兰 Cyrtosia javanica | Lee et al., 2015 | |||||
| 附毛菌属 Trichaptum | 倒吊兰 Erythrorchis altissima | Ogura-Tsujita et al., 2018 | ||||||
| 油伏革菌属 Resinicium | Gastrodia similis | Martos et al., 2009 | ||||||
| Hydropus | 夏天麻 Gastrodia flabilabella | Lee et al., 2015 | ||||||
| 小菇属 Mycena | Gastrodia confuse, 无喙天麻 G. appendiculata, 春天麻 G. fontinalis, G. nantoensis, Wullschlaegelia aphylla | Martos et al., 2009; Ogura-Tsujita et al., 2009; Lee et al., 2015 | ||||||
| 小脆柄菇属 Psathyrella | 虎舌兰 Epipogium roseum, 无叶美冠兰 Eulophia zollingeri | Yamato et al., 2005; Ogura-Tsujita et al., 2008 | ||||||
| 鬼伞属 Coprinus | 虎舌兰 Epipogium roseum | Yamato et al., 2005 | ||||||
| Gymnopus | Wullschlaegelia aphylla | Martos et al., 2009 | ||||||
| 外生菌根真菌Ectomycorrhizal fungi | 子囊菌纲 Ascomycetes | 火丝菌科 Pyronemataceae | 火烧兰 Epipactis helleborine | Stöckel et al., 2014 | ||||
| Wilcoxina | Epipactis atrorubens, E. distans | Bidartondo et al., 2004; Schiebold et al., 2017 | ||||||
| Tuber | Epipactis atrorubens, 火烧兰 E. helleborine, E. microphylla, E. muelleri, E. leptochila, E. neglecta | Bidartondo et al., 2004; Selosse, et al., 2004; Stöckel et al., 2014; Schiebold et al., 2017 | ||||||
| 柔膜菌目 Helotiales | 火烧兰 Epipactis helleborine | Schiebold et al., 2017 | ||||||
| Craterellus | Dactylorhiza majalis | Schweiger et al., 2018 | ||||||
| 担子菌纲 Basidiomycetes | 蜡壳耳目 Sebacinales | 尾萼无叶兰 Aphyllorchis caudata | Roy et al., 2009a | |||||
| 蜡壳耳属 Sebacina | Lecanorchis japonica var. hokurikuens, L. trachycaula, L. flavicans var. flavicans, Epipactis microphylla, 火烧兰 E. helleborine, Neottia nidus-avis | Bidartondo et al., 2004; Okayama et al., 2012; Stöckel et al., 2014; Schiebold et al., 2017; Schweiger et al., 2018 | ||||||
| 真菌类型 Fungi type | 真菌分类群 Fungi taxon | 兰科植物 Orchid | 参考文献 Reference | |||||
| 纲 Class | 目 Order | 科 Family | 属 Genus | |||||
| 外生菌根真菌Ectomycorrhizal fungi | 革菌科 Thelephoraceae | 尾萼无叶兰 Aphyllorchis caudate, 无叶兰 A. montana, Cephalanthera exigua, C. austinae, 火烧兰 Epipactis helleborine, 头蕊兰 C. longifolia | Taylor & Bruns, 1997; Abadie et al., 2006; Roy et al., 2009a; Schiebold et al., 2017 | |||||
| 棉革菌属 Tomentella | Cephalanthera rubra, 大花头蕊兰 C. damasonium, 珊瑚兰 Corallorhiza trifida, 火烧兰 Epipactis helleborine | Bidartondo et al., 2004; Zimmer et al., 2008; Stöckel et al., 2014; Schiebold et al., 2017 | ||||||
| 革菌属 Thelephora | 大花头蕊兰 Cephalanthera damasonium | Bidartondo et al., 2004 | ||||||
| Craterellus | Dactylorhiza majalis | Schweiger et al., 2018 | ||||||
| Hydnum | Dactylorhiza majalis | Schweiger et al., 2018 | ||||||
| 红菇科 Russulaceae | 尾萼无叶兰 Aphyllorchis caudate, 无叶兰 A. montana, Cephalanthera maculata | Taylor & Bruns, 1997; Roy et al., 2009a | ||||||
| 红菇属 Russula | 倒吊兰 Erythrorchis altissima, Lecanorchis flavicans var. acutiloba, L. nigricans, L. trachycaula, L. japonica var. hokurikuens, L. japonica var. japonica, L. japonica var. kiiensis, L. kiusiana var. kiusiana, Cephalanthera maculate, Epipactis purpurata | Taylor & Bruns, 1997; Okayama et al., 2012; Schiebold et al., 2017; Ogura-Tsujita et al., 2018 | ||||||
| Lactarius | Cephalanthera maculate, 裂唇虎舌兰 Epipogium aphyllum, Lecanorchis japonica var. hokurikuens, L. japonica var. japonica, L. japonica var. kiiensis, L. kiusiana var. kiusiana, L. kiusiana var. suginoana, L. virella, L. trachycaula, L. nigricans | Taylor & Bruns, 1997; Roy et al., 2009b; Liebel & Gebauer, 2011; Okayama et al., 2012 | ||||||
| 裸腹菌属 Gymnomyces | Cephalanthera maculata | Taylor & Bruns, 1997 | ||||||
| 丝膜菌科 Cortinariaceae | 头蕊兰 Cephalanthera longifolia | Abadie et al., 2006 | ||||||
| 丝膜菌属 Cortinarius | Epipactis microphylla, 大花头蕊兰 Cephalanthera damasonium | Bidartondo et al., 2004; Selosse et al., 2004; Schiebold et al., 2017 | ||||||
| 丝盖伞属 Inocybe | Epipactis atrorubens, 火烧兰 E. helleborine, E. helleborine subsp. Neerlandica, E. purpurata, 裂唇虎舌兰 Epipogium aphyllum, 大花头蕊兰 Cephalanthera damasonium | Bidartondo et al., 2004; Roy et al., 2009b; Liebel & Gebauer, 2011; Schiebold et al., 2017 | ||||||
| Hebeloma | 裂唇虎舌兰 Epipogium aphyllum | Roy et al., 2009b; Liebel & Gebauer, 2011 | ||||||
| 层腹菌属 Hymenogaster | 大花头蕊兰 Cephalanthera damasonium | Bidartondo et al., 2004 | ||||||
| 阿泰菌科 Atheliaceae | Lecanorchis flavicans var. acutiloba, L. trachycaula | Okayama et al., 2012 | ||||||
| Amphinema | 头蕊兰 Cephalanthera longifolia | Abadie et al., 2006 | ||||||
| Clavulinaceae | 无叶兰 Aphyllorchis montana | Roy et al., 2009a | ||||||
| 角担菌属 Ceratobasidium | Chamaegastrodia sikokiana | Yagame et al., 2008 | ||||||
| 内生真菌 Endophytes | 子囊菌纲 Ascomycetes | 丛赤壳科 Nectriaceae | 头蕊兰 Cephalanthera longifolia | Abadie et al., 2006 | ||||
| 土赤壳属 Ilyonectria | 黄蜂兰 Ophrys insectifera | Schweiger et al., 2018 | ||||||
| Phialophora | 二叶舌唇兰 Platanthera chlorantha, Epipactis atrorubens, Cephalanthera rubra, 头蕊兰 C. longifolia | Bidartondo et al., 2004; Abadie et al., 2006 | ||||||
| Phialocephala | Dactylorhiza majalis | Schweiger et al., 2018 | ||||||
| Exophiala | 手参 Gymnadenia conopsea | Schweiger et al., 2018 | ||||||
| 担子菌纲 Basidiomycetes | Botryobasidium | 剑叶拟兰 Apostasia wallichii, A. cf. wallichii, 拟兰 A. odorata | Yukawa et al., 2009 | |||||
| 半知菌类 Imperfect fungi | Leptodontidium | 新疆火烧兰 Epipactis palustris, E. atrorubens, 二叶舌唇兰 Platanthera chlorantha, 红花头蕊兰 Cephalanthera rubra | Bidartondo et al., 2004 | |||||
2.1 腐生真菌
腐生真菌是生态系统的分解者。森林中的腐生真菌主要从落叶、枯枝、树根等无生命的有机质中获取营养物质。营腐生的OM真菌可以分为2类: 类丝核菌和非类丝核菌的腐生真菌(以下简称“SAP真菌”)。类丝核菌是占物种数量大多数的自养型兰科植物的优势菌根真菌, SAP真菌主要与少数真菌异养型兰科植物形成共生关系。
2.1.1 类丝核菌
类丝核菌是兰科植物特有的一类OM真菌(Yukawa et al., 2009), 也是兰科植物最主要和最古老的共生真菌(Taylor & Gebauer, 2002)。但是, 类丝核菌对这种共生关系的依赖程度较低, 可以脱离兰科植物单独培养; 另外, 绿色兰科植物也会随着环境条件的变化而与不同的真菌合作(Motomura et al., 2010; Dearnaley et al., 2012; Martos et al., 2012)。类丝核菌营寄生或腐生生活; 有些类丝核菌的生活史中既有营腐生的独立生活时期, 也有营寄生的内生生活时期(Dearnaley et al., 2012; Merckx, 2013)。需要注意的是, 类丝核菌不是一个分类学概念。分子系统发育分析表明, 与兰科植物共生的类丝核菌包含了担子菌门胶膜菌科、角担菌科及蜡壳耳目的真菌(Abadie et al., 2006; Dearnaley et al., 2012; Merckx, 2013)。胶膜菌科是热带和温带地区最常见的OM真菌, 也是地生和附生兰科植物常见的共生真菌(Yuan et al., 2010; Martos et al., 2012; Herrera et al., 2018)。蜡壳耳目主要分为A和B两个亚类群, 已报道的蜡壳耳目类丝核菌都归属于B亚类群, 是能够与兰科和杜鹃花科植物共生的植物内生菌, 通常很难形成子实体(Weiß et al., 2011, 2016)。
2.1.2 SAP真菌
根据营养物质的来源, OM真菌中的SAP真菌可以分为木质分解菌和凋落物分解菌。20世纪初研究者已经发现完全真菌异养型的天麻与木质分解菌蜜环菌(Armillaria mellea)的共生关系(Kusano, 1911)。生活在热带及亚热带森林, 环境中缺少EcM真菌群落的完全真菌异养型和部分真菌异养型兰科植物通过与SAP真菌共生直接获得营养, 这种关系被称为“菌根寄生” (Ogura-Tsujita et al., 2009)。Martos等(2009)报道, 完全真菌异养型兰科植物Wullschlaegelia aphylla与裸脚菇属(Gymnopus spp.)和小菇属真菌(Mycena spp.)等凋落物分解菌共生, 菌索在W. aphylla根与落叶之间建立起了物理联系。目前报道小菇属、蜜环菌属、小皮伞属(Marasmius)、层孔菌属(Fomes)、Resinicium、Campanella、Gymnopus和Hydropus等SAP真菌类群可以与天麻属及其近似属双唇兰属(Didymoplexis)的植物形成“菌根寄生”关系(徐锦堂和牟春, 1990; Sekizaki et al., 2008; Martos et al., 2009; Ogura-Tsujita et al., 2009; Lee et al., 2015; Chen et al., 2019), 它们中既有木质分解菌, 也有凋落物分解菌。此外, 2种凋落物分解菌Trichaptum cf. durum和Coniophorafomes matsuzawae是倒吊兰属倒吊兰(Erythrorchis altissima)的主要真菌伙伴(Ogura-Tsujita et al., 2018); 小脆柄菇属(Psathyrella)的一些凋落物分解菌是虎舌兰属Epipogium roseum和美冠兰属Eulophia zollingeri的真菌伙伴(Yamato et al., 2005; Ogura-Tsujita & Yukawa, 2008)。
2.2 外生菌根真菌(EcM真菌)
EcM是松科、被子植物灌木及乔木等植物的根与真菌形成的菌根共生体, 是温带森林中树木的优势菌根类型。EcM的特征是: 真菌菌丝在根表面蔓延形成菌鞘; 部分菌丝在根皮层细胞间隙形成哈蒂氏网; 但真菌不侵入根细胞内(Liebel & Gebauer, 2011; van der Heijden et al., 2015)。兰科植物与EcM的关系被描述为“菌根外寄生”, 即兰科植物寄生在EcM共生体上, 形成兰科植物-EcM真菌-树木的三元共生系统(Liebel & Gebauer, 2011)。通过“菌根外寄生”方式, 兰科植物既能获得EcM真菌的矿质营养, 也能通过EcM获得树木的光合产物, 从而使其能够在低光照的林下环境中正常生长(Bidartondo et al., 2004; Ogura-Tsujita et al., 2009; Bougoure et al., 2010)。Bidartondo等(2004)认为, 兰科植物进化中, 招募环境中的EcM真菌成为其合作伙伴应该是先于植物丧失光合作用能力发生的事件。
目前发现的能与兰科植物合作的EcM真菌类群主要包括: 担子菌门革菌目(Thelephorales)、红菇目(Russulales)、伞菌目(Agaricales)、蜡壳耳目A亚类群和鸡油菌目(Cantharellales)角担菌属(Ceratobasidium)等(Dearnaley et al., 2012), 以及子囊菌门锤舌菌纲(Leotiomycetes)和盘菌纲(Pezizomycetes)(Hynson & Bruns, 2010; Weiß et al., 2011; Dearnaley et al., 2012; Hynson et al., 2013), 其中担子菌较子囊菌有更强的宿主专一性(Hynson & Bruns, 2010)。大多数与EcM真菌共生的完全真菌异养型兰科植物生长在温带森林, 少数生长在热带及亚热带森林; 它们主要来自鸟巢兰属(Neottia)、头蕊兰属、盂兰属(Lecanorchis)、珊瑚兰属(Corallorhiza)、无叶兰属(Aphyllorchis)和虎舌兰属等(Taylor & Bruns, 1997; McKendrick et al., 2002; Roy et al., 2009a, 2009b; Motomura et al., 2010; Okayama et al., 2012)。目前的研究显示, 温带兰科植物与EcM真菌的专一性更强, 热带及亚热带兰科植物能与更广泛的EcM真菌类群合作(Dearnaley et al., 2012)。
3 不同营养方式兰科植物的氮营养特征
3.1 同位素分析技术在兰科植物营养研究中的应用
具有不同相对原子质量的同位素在化学、生物等反应中以不同比例分配于反应物和产物之间的现象被称为“同位素分馏” (Baskaran, 2011)。生物的分泌作用和呼吸作用有利于12C和14N排出体外, 从而导致重同位素13C和15N在生物体中富集(Leake & Cameron, 2010)。包括OM真菌在内的所有菌根真菌都有富集重同位素的特性(Gebauer & Dietrich, 1993), 因此同位素分馏现象被广泛用于研究营养元素在菌根共生体中迁移的源汇关系, 说明营养元素在共生体合作双方的分配比例。实际研究中用样品中目标元素的富集因子(δ)表示样品的同位素成分, δ的含义为: 样品同位素比值(RSp)相对于标准物质同位素比值(RSt)的千分差:
δ (‰) = (RSp/RSt - 1) × 1000
式中, 同位素比值(R)表示某一元素的重同位素原子丰度与轻同位素原子丰度之比。
表2 基于同位素实验的兰科植物营养方式
Table 2
| 营养方式 Trophic mode | 亚科 Subfamily | 属 Genus | 种 Species | 参考文献 Reference |
|---|---|---|---|---|
| 完全真菌异养型 Fully mycoheterotrophy | 香荚兰亚科 Vanilloideae | 盂兰属 Lecanorchis | L. nigricans | Motomura et al., 2010; Hynson et al., 2016 |
| L. thalassica | Lee et al., 2015; Hynson et al., 2016 | |||
| 肉果兰属 Cyrtosia | 肉果兰 C. javanica | Lee et al., 2015 | ||
| 山珊瑚属 Galeola | 直立山珊瑚 G. falconeri | Lee et al., 2015 | ||
| 倒吊兰属 Erythrorchis | E. altissima | Ogur-Tsujita et al., 2018 | ||
| 兰亚科 Orchidoideae | 长药兰属 Serapias | S. parviflora | Stöckel et al., 2014 | |
| Pseudorchis | P. albida | Stöckel et al., 2014 | ||
| 树兰亚科 Epidendroideae | 鸟巢兰属 Neottia | 鸟巢兰 N. nidus-avis | Bidartondo et al., 2004; Preiss et al., 2010; Hynson et al., 2016 | |
| 天麻属 Gastrodia | G. confuse | Ogura-Tsujita et al., 2009; Hynson et al., 2013 | ||
| G. similis | Martos et al., 2009; Hynson et al., 2013 | |||
| G. flabilabella | Lee et al., 2015 | |||
| 无喙天麻 G. appendiculata | Lee et al., 2015 | |||
| G. fontinalis | Lee et al., 2015 | |||
| G. nantoensis | Lee et al., 2015 | |||
| Wullschlaegelia | W. aphylla | Martos et al., 2009 | ||
| 虎舌兰属 Epipogium | 裂唇虎舌兰 E. aphyllum | Liebel & Gebauer, 2011; Hynson et al., 2016 | ||
| 兰属 Cymbidium | C. macrorhizon* | Motomura et al., 2010; Hynson et al., 2016 | ||
| C. aberrans* | Motomura et al., 2010; Hynson et al., 2016 | |||
| 无叶兰属 Aphyllorchis | A. caudata | Roy et al., 2009a; Hynson et al., 2016 | ||
| 无叶兰 A. montana | Roy et al., 2009a; Hynson et al., 2016 | |||
| 头蕊兰属 Cephalanthera | C. exigua | Roy et al., 2009a; Hynson et al., 2016 | ||
| 珊瑚兰属 Corallorhiza | 夏珊瑚兰 C. maculata | Trudell et al., 2003; Hynson et al., 2016 | ||
| 营养方式 Trophic mode | 亚科 Subfamily | 属 Genus | 种 Species | 参考文献 Reference |
| 部分真菌异养型/混合营养型 Partially mycoheterotrophy/ mixotrophy | 兰亚科 Orchidoideae | 唇舌兰属 Platanthera | P. bifolia* | Gebauer & Meyer, 2003; Tedersoo et al., 2007; Schweiger et al., 2018 |
| 小唇舌兰 P. minor* | Zimmer et al., 2007; Hynson et al., 2016 | |||
| 掌裂兰属 Dactylorhiza | D. sambucina* | Gebauer & Meyer, 2003 | ||
| 蜂兰属 Ophrys | O. insectifera* | Gebauer & Meyer, 2003; Schweiger et al., 2018 | ||
| 树兰亚科 Epidendroideae | 兰属 Cymbidium | C. goeringii* | Motomura et al., 2010; Hynson et al., 2016 | |
| 兔耳兰 C. lancifolium* | Motomura et al., 2010; Hynson et al., 2016 | |||
| 头蕊兰属 Cephalanthera | C. damasonium | Gebauer & Meyer, 2003; Bidartondo et al., 2004; Preiss et al., 2010 | ||
| C. longifolia* | Abadie et al., 2006; Hynson et al., 2016 | |||
| C. rubra* | Gebauer & Meyer, 2003; Bidartondo et al., 2004; Preiss et al., 2010; Hynson et al., 2016 | |||
| 银兰 C. erecta* | Motomura et al., 2010; Hynson et al., 2016 | |||
| 珊瑚兰属 Corallorhiza | 珊瑚兰 C. trifida* | Zimmer et al., 2008 | ||
| 火烧兰属 Epipactis | E. atrorubens* | Gebauer & Meyer, 2003; Bidartondo et al., 2004; Hynson et al., 2016 | ||
| E. helleborine* | Bidartondo et al., 2004; Stöckel et al., 2014; Hynson et al., 2016; Schiebold et al., 2017 | |||
| E. distans* | Bidartondo et al., 2004; Hynson et al., 2016; Schiebold et al., 2017 | |||
| E. gigantea | Zimmer et al., 2007; Schiebold et al., 2017 | |||
| E. neglecta | Schiebold et al., 2017 | |||
| E. helleborine subsp. neerlandica | Schiebold et al., 2017 | |||
| E. microphylla | Schiebold et al., 2017 | |||
| E. purpurata | Schiebold et al., 2017 | |||
| E. leptochila | Schiebold et al., 2017 | |||
| E. muelleri | Schiebold et al., 2017 | |||
| 丛宝兰属 Limodorum | 丛宝兰 L. abortivum | Gebauer & Meyer, 2003; Hynson et al., 2016 | ||
| 对叶兰属 Listera | L. ovata* | Gebauer & Meyer, 2003; Tedersoo et al., 2007 | ||
| 自养型 Autotrophy | 杓兰亚科 Cypripedioideae | 杓兰属 Cypripedium | 杓兰 C. calceolus | Preiss et al., 2010 |
| 兰亚科 Orchidoideae | 舌唇兰属 Platanthera | P. chlorantha | Bidartondo et al., 2004 | |
| P. leucostachys* | Zimmer et al., 2007 | |||
| 掌裂兰属 Dactylorhiza | D. majalis* | Bidartondo et al., 2004; Schweiger et al., 2018 | ||
| 斑叶兰属 Goodyera | G. oblongifolia | Zimmer et al., 2007 | ||
| 手参属 Gymnadenia | 手参 G. conopsea | Schweiger et al., 2018 | ||
| 红门兰属 Orchis | O. militaris | Schweiger et al., 2018 | ||
| O. ustulata* | Gebauer & Meyer, 2003 | |||
| O. mascula* | Gebauer & Meyer, 2003 | |||
| 拟兰亚科 Epidendroideae | 火烧兰属 Epipactis | E. palustris* | Bidartondo et al., 2004 |
*, 植物的营养型经过双源同位素混合模型验证; 未标注植物的营养型经过13C、15N同位素分析。
*, The trophic mode of orchids were verified by two-source isotopic mixing model; the trophic mode of unlabeled orchids were verified by 13C, 15N stable isotope analysis.
目前研究表明, 通常情况下兰科植物的氮含量高, 15N丰度高。在兰科植物真菌异养的幼年阶段, 原球茎氮含量显著高于成年植株(Stöckel et al., 2014)。完全真菌异养型兰科植物的氮含量显著高于环境中的其他自养植物, 15N丰度和δ15N与它们真菌伙伴的十分接近(Gebauer & Meyer, 2003; Trudell et al., 2003; Bougoure et al., 2010)。分析δ13C和δ15N发现, 真菌异养型兰科植物的δ13C能反映出植物对真菌碳源的依赖程度, 但植物氮同化的情况则比较复杂。与环境中的其他自养型植物相比, 许多真菌异养型兰科植物明显富集15N; 但是15N富集并不是真菌异养型植物的普遍特征, 15N富集程度也并不总是与植物的真菌异养程度呈线性正相关关系(Leake & Cameron, 2010)。有研究表明, 真菌异养型兰科植物的15N富集能力与菌根真菌的生态功能密切相关。一般情况下, EcM真菌比SAP真菌有更强的15N富集能力; EcM真菌中, 能够利用有机氮的真菌比偏好利用无机氮的真菌有更强的15N富集能力; 具有宿主特异性的真菌比非宿主特异性真菌有更强的15N富集能力(Hobbie et al., 2005; Tedersoo et al., 2007; Hynson et al., 2013; Schweiger et al., 2018)。
3.2 真菌异养型兰科植物的氮营养特征
目前发现的完全真菌异养型兰科植物的数量是很少的。由于15N和13C稳定同位素研究的技术还有待完善, 研究者多认为从部分真菌异养型向完全真菌型异养过渡和进化的兰科植物的数量被低估了(Schweiger et al., 2019; Wang et al., 2021)。据Jacquemyn和Merckx (2019)推测, 约有580种无叶植物是完全或接近于完全真菌异养的, 其中兰科植物约有295种。随着同位素技术的广泛应用, 陆续发现一些曾被认为是完全真菌异养的植物, 在某个特定发育时期具有部分光合自养的能力(Zimmer et al., 2008; Motomura et al., 2010; Suetsugu et al., 2018)。
大多数绿色兰科植物是部分真菌异养的, 部分真菌异养并非是一种静态的营养模式。它们被认为是由自养型植物向完全真菌异养型植物进化的过渡类型/中间类型(Motomura et al., 2010; Schiebold et al., 2018)。拟兰亚科(Epidendroideae)是兰科中最为原始的类群, Suetsugu和Matsubayashi (2021)报道Apostasia nipponica作为绿色兰科植物, 其δ15Ν高于与EcM共生的完全异养植物, 证明其为部分异养植物。Wang等(2021)报道至少17种以上兰科植物由自养进化到了完全真菌异养, 其中大多数处于部分真菌异养的过渡状态。
对兰科和杜鹃花科植物的研究表明, 部分真菌异养型植物富集15N的作用较其富集13C的作用更明确, 植物的δ15N介于自养型植物和完全真菌异养型植物之间, 有时甚至高于完全真菌异养型植物(Tedersoo et al., 2007)。
3.2.1 与EcM真菌合作的真菌异养型兰科植物
EcM真菌优先从土壤吸收氮营养, 土壤的氮含量较枯木、落叶等基质的高。此外, EcM真菌既能吸收无机氮(NH4+和NO3-), 也能吸收有机氮(氨基酸、蛋白质、几丁质等), 可以利用的氮营养形式较SAP真菌更加丰富。因此, EcM真菌子实体δ15N高于基质氮素贫瘠的SAP真菌和以吸收无机氮为主的自养型植物。Trudell等(2003)报道, 与EcM真菌共生的完全真菌异养型兰科植物的δ15N较EcM真菌子实体的平均值提高了3‰-4‰, 且两者之间显著正相关(p < 0.05), 植物与子实体的δ13C则很接近; 研究者认为, 真菌细胞质含有蛋白质和氨基酸等富氮成分, 兰科植物根皮层细胞消化衰老菌丝圈的特点, 使得植物能够吸收真菌胞质的氮从而表现出富集15N的特征。在Schiebold等(2017)的研究中, 子囊菌类及担子菌类EcM真菌, 以及腐生真菌子实体的δ15N分别为10.7‰ ± 2.2‰、5.2‰ ± 4.0‰和3.3‰ ± 2.1‰; 部分真菌异养的8种火烧兰属植物叶的δ15N从3.2‰ ± 0.8‰到24.6‰ ± 1.6‰不等, 其中, δ15N最高的是只与子囊菌类EcM真菌共生的植物, 其次是与子囊菌类和担子菌类EcM真菌都有联系的植物, 再次是只与担子菌类EcM真菌联系的植物, 与类丝核菌联系的植物的δ15N最低。
3.2.2 与SAP真菌合作的真菌异养型兰科植物
到目前为止, 仅发现兰科植物能与SAP真菌合作(Leake & Cameron, 2010), 其中天麻族和香荚兰族与SAP真菌密切相关(Hynson & Bruns, 2010)。与SAP真菌合作的完全真菌异养型兰科植物常表现出对菌根真菌更强的适应能力。天麻在种子萌发阶段是与小菇属真菌合作, 进入成年阶段转为与蜜环菌合作(徐锦堂和牟春, 1990)。倒吊兰属藤本植物E. cassythoides在其攀附的树木死亡后, 合作的真菌伙伴由EcM真菌转变为SAP真菌(Dearnaley, 2006)。SAP真菌从树桩、枯树枝、落叶等获取营养, 这些基质中碳素丰富而氮素贫瘠; 因此SAP真菌子实体的δ13C通常高于EcM真菌子实体, 而δ15N显著低于EcM真菌(Trudell et al., 2003; Pritsch & Garbaye, 2011)。与SAP真菌合作的兰科植物的同位素信号特点是: δ13C较生境中其他自养植物的有显著提高, 数值之间差距明显; δ15N较生境中其他自养植物略有提高, 两者之间δ15N的差距小于与EcM真菌合作的兰科植物与生境中其他自养植物之间δ15N的差距。
关于木质分解菌与凋落物分解菌对兰科宿主植物15N富集作用影响的差异, 目前的研究尚未形成统一认识。一些报道中, 这两类真菌的宿主植物富集15N的能力没有差异。比如, Lee等(2015)报道, 与木质分解菌合作的3种兰科植物直立山珊瑚(Galeola falconeri)、肉果兰(Cyrtosia javanica)、夏天麻(G. flabilabella)较与凋落物分解菌合作的3种兰科植物春天麻(G. fontinalis)、G. nantoensis、无喙天麻(G. appendiculata)的δ13C平均提高约3‰; 但两类植物的δ15N之间几乎没有差异, 而与木质分解菌合作的3种兰科植物与EcM真菌合作的兰科植物Lecanorchis thalassica的δ15N相比, 平均减少了约3.5‰。另一些报道中, 与凋落物分解菌合作的真菌异养型兰科植物有更强的15N富集能力。比如, Martos等(2009)报道, 同为完全真菌异养型植物, 与木质分解菌Resinicium spp.合作的天麻属植物G. similis较取样环境中非兰科绿色植物的δ15N提高了1.4‰-3.2‰, 主要与小菇类凋落物分解菌合作的W. aphylla较取样环境中非兰科绿色植物的δ15N提高了5.4‰。
3.3 自养型兰科植物的氮营养特征
成年后, 大多数兰科植物能够通过光合作用获取碳营养, 但仍需要真菌为其提供氮营养(Gebauer & Meyer, 2003)。自养型兰科植物也具有富集15N的特性, 植株氮含量显著高于环境中的非兰科自养植物, δ15N介于非兰科自养植物和完全真菌异养型兰科植物之间(Dearnaley et al., 2012; Hynson et al., 2013; Schweiger et al., 2018)。尽管从自养型兰科植物根部往往能同时检测到类丝核菌、EcM真菌和SAP真菌, 但类丝核菌被认为是这类植物的共生真菌(Dearnaley et al., 2012)。Zimmer等(2007)报道, 舌唇兰属植物Platanthera leucostachys叶片中25%-32%的氮来自真菌, 没有真菌来源的碳, 该植物的δ15N较生境中其他非兰科自养植物有显著提高, 但显著低于完全真菌异养的珊瑚兰属植物夏珊瑚兰(Corallorhiza maculata)。Bidartondo等(2004)报道, 2种绿色兰科植物: 新疆火烧兰(E. palustris)和根爪兰属的Dactylorhiza majalis, 它们叶片中真菌来源氮的占比分别为30% ± 2%和26% ± 6%, δ15N较生境中非兰科自养植物均有显著提高; 真菌来源碳的占比分别为-2% ± 7%和-8% ± 16%, δ13C与生境中非兰科自养植物没有显著差异。
4 OM共生体中的氮转移机制
兰科植物氮营养的特征与真菌通过OM共生体向植物提供氮营养的作用机制密切相关。与AM中氮在丛枝膜和丛枝前体质膜上的跨膜转运不同, OM中氮还可以通过OM真菌菌丝圈裂解被宿主细胞吸收(Gebauer & Meyer, 2003; Bougoure et al., 2010)。这是兰科植物特有的一种营养运输机制。对于OM中氮营养转移机制的认识经历了2个阶段。早期的观点认为, 氮是单向从真菌向植物转移的: 成熟而健康的真菌通过OM将有机氮和无机氮传递给植物细胞(Cameron et al., 2006; Kuga et al., 2014); 随着真菌的衰老, 菌丝圈退化、降解, 释放出大量碳、氮和磷等养分被植物细胞吸收和利用(郭顺星和徐锦堂, 1990; 徐锦堂和牟春, 1990; Zimmer et al., 2007)。近年的研究发现, 氮在植物和真菌之间可以双向流动, 真菌主要向植物提供有机氮, 并通过菌丝团与植物细胞内的非原生质体共质界面从植物细胞获取无机氮(NH4+)(Dearnaley & Cameron, 2017)。
有关OM共生体的氮营养转移形式, 现有的研究表明, 一方面, OM真菌能够促进植物对无机氮营养的吸收和同化。Wu等(2013)报道, 根部接种了类丝核菌的春兰(Cymbidium goeringii)盆栽幼苗吸收无机氮的形式发生了转变, 从以吸收NO3-为主转变为偏好吸收NH4+; 同时, 植物吸收甘氨酸的能力提高。Hajong等(2013)报道, 在燕麦培养基上与类丝核菌共生培养提高了石斛属束花石斛(Dendrobium chrysanthum)幼苗叶片的硝酸还原酶和亚硝酸还原酶活性, 从而增强了植物的氮同化能力。Shan等(2021)报道, 与小菇属菌株MF23 (Mycena sp.)共生培养的铁皮石斛(D. officinale)根系吸收NH4+和NO3-的速度提高, 谷氨酰胺合成酶和谷氨酸脱氢酶的活性增强, 推测MF23通过促进对氮的吸收和同化促进植物生长, 提高生物量。另一方面, 有机氮是OM真菌为宿主提供的主要氮营养形式。这可能是由于有机氮能够同时满足宿主对碳和氮的需求, 是一种更高效的营养形式。王秋霞等(2014)报道, 接种Epulorhiza sp.提高了金钗石斛(D. nobile)幼苗对15N标记甘氨酸的吸收和利用。Alghamdi (2020)报道, 与OM真菌共生时, 在含标记氨基酸的培养基上生长的倒矩兰属Anacamptis palustris和A. laxiflora的生物量和体内13C和15N丰度均显著高于在含标记NH4NO3和葡萄糖的培养基上生长的植物的, 表明共生体吸收和同化氨基酸的能力更强。Cameron等(2006)阐明了斑叶兰属小斑叶兰(Goodyera repens)通过真菌Ceratobasidium cornigerum获取氮营养的途径, 认为13C和15N双标记甘氨酸是作为碳源, 而不是氮源, 被真菌根外菌丝吸收, 再传递给植物的。
Fochi等(2017a, 2017b)的研究表明, 在兰科植物Serapias vomeracea原球茎与OM真菌美孢胶膜菌(Tulasnella calospora)共生的情况下, 真菌的铵转运蛋白(AMT)基因TcAMT2, 参与NH4+合成的谷氨酰胺合成酶(GS)基因TcGS1, 以及氨基酸转运蛋白(AAT)基因TcAAT1、TcAAT2和TcAAT6显著上调表达, 原球茎的铵转运蛋白基因SvAMT1显著上调表达, 含成熟、完整菌丝圈的原球茎细胞中氨基酸通透酶(AAPs)基因SvAAP1和SvAAP2, 以及赖氨酸组氨酸转运蛋白(LHTs)基因SvLHT显著上调表达; 表明二者共生后, 双方体内的氮代谢相关基因变化剧烈。结合美孢胶膜菌在有机氮源培养基上生长速度更快, 以及美孢胶膜菌基因组缺少硝酸盐同化相关基因等特性, Fochi等(2017a, 2017b)认为, 在美孢胶膜菌-S. vomeracea原球茎的共生体中, 真菌向原球茎主要提供有机氮, 原球茎向真菌回馈NH4+, 植物-真菌共生后, 关于氮代谢的相关基因不仅在植物中发生变化, 在真菌中也发生变化。
5 展望
与真菌形成菌根是兰科植物的共同特征。OM是兰科植物特有的一种内生菌根类型。兰科植物要经历一段真菌异养的幼苗期, 种子萌发形成的原球茎完全依赖细胞内定殖的OM真菌提供碳、氮等营养物质。近年研究发现了共生萌发形成的原球茎中结构完整、发育成熟的OM真菌与原球茎细胞之间碳、氮交换的基本形式和方向, 首次阐明了OM的生理作用(Kuga et al., 2014)。绝大多数成年绿色兰科植物是自养的。同位素分析结果证明, 这个阶段的兰科植物能向OM真菌回馈部分光合产物, 但体内仍有比例可观的氮是来自OM真菌的。目前有关成年阶段OM对植物矿质营养吸收和同化作用的研究, 在数量和深度上都不及异养幼苗阶段。这一现状与兰科植物生长条件苛刻, 繁殖方式特殊, 生命周期长和成年阶段营养方式的多样化有一定关系。开展成年植物氮、磷等矿质营养的研究能促进对兰科自然资源的保护和恢复, 并为研究建立高效的人工繁育技术奠定理论基础。
随着对兰科植物研究的深入, 不断有新的有关OM共生体互作的有趣问题出现。首先, 目前已发现的OM真菌主要包括来自伞菌纲Agaricomycetes和盘菌纲Pezizomycetes的腐生真菌(包括类丝核菌和SAP真菌), 以及在一些无叶绿素的异养兰科植物中出现的多个EcM真菌类群。系统发育分析的研究表明: 类丝核菌是最古老的OM真菌, 物种数量占据绝对多数的绿色兰科植物主要与类丝核菌共生; EcM真菌是兰科植物最新“招募”的一类OM真菌, 终生保留异养特性的兰科植物, 包括部分异养的和完全异养的, 主要与SAP真菌和/或EcM真菌共生(Dearnaley et al., 2012)。那么, 采取不同营养策略的OM真菌分别通过什么途径和方式与宿主植物细胞交流碳、氮等营养物质? 其次, 对天麻的研究发现, 天麻的种子萌发菌是小菇属真菌, 而它地下块茎的生长发育则取决于原球茎能否与适宜的蜜环菌属真菌建立共生关系(徐锦堂和牟春, 1990)。通过对天麻人工繁殖技术的研究, 人们已经了解到在不同生长阶段依赖不同共生真菌是天麻完成生活史所必需的, 但是对产生这种现象的原因还不得而知。此外, 不论是天麻在不同生长阶段改变共生真菌, 还是更具普遍性的自养兰科植物在不同生长阶段改变营养方式, 它们会对兰科植物的碳、氮吸收同化及生长发育产生哪些影响? 对上述问题的研究将有助于我们更深刻地理解兰科植物和共生真菌的营养关系, 理解兰科植物的生物特点。
参考文献
Cephalanthera longifolia (Neottieae, Orchidaceae) is mixotrophic: a comparative study between green and nonphotosynthetic individuals
DOI:10.1139/b06-101 URL [本文引用: 12]
Biological role of mycorrhizal fungi on the assimilation and transportation of carbon and nitrogen to Anacamptis palustris and Anacamptis laxiflor
DOI:10.1016/j.sjbs.2019.11.010
PMID:31889872
[本文引用: 1]
Fungal is a physiological trail and its understanding in the assimilation with the transfer of carbon (C) cum nitrogen (N) or (C/N) to orchid-seedlings have not been determined. Labelled stable isotopes C and N were used to plan the flow of C and N between orchid plants and mycorrhizal connotations in-terms of bulk transfer for C/N. This study attends to comprehend the mechanism, supporting mycorrhizal fungi which influences on orchid-seedling growth. Determined integration and transfer of C/N from amino acids (AA), ammonium nitrate (NHNO) and sugar for orchid-plant may lead to understand these mechanisms. This current study tries to estimate the importance of organic compounds as a source for C/N over the inorganic-NHNO. Generally, after begging of germination and when it is found to be associated to the nutrient resource, organic compound enhance the biomass accumulation of two orchid species. AA significantly increase the mass of C assimilated by two species. With amino acids the concentration of C in two species was greater than with NHNO and sugar. At another phase, amount of N content shoots was a higher value in shoots assimilated substantially additional of N with NHNO plus sugar compared with ammonium nitrate only. This study showed that two terrestrial orchids species are reliant on organic compounds as a source of carbon and nitrogen more than inorganic compounds.© 2019 Published by Elsevier B.V. on behalf of King Saud University.
Changing partners in the dark: isotopic and molecular evidence of ectomycorrhizal liaisons between forest orchids and trees
DOI:10.1098/rspb.2004.2807 URL [本文引用: 24]
Carbon and nitrogen supply to the underground orchid, Rhizanthella gardneri
DOI:10.1111/j.1469-8137.2010.03246.x
PMID:20353419
[本文引用: 3]
*Rhizanthella gardneri is a rare and fully subterranean orchid that is presumably obligately mycoheterotrophic. R. gardneri is thought to be linked via a common mycorrhizal fungus to co-occurring autotrophic shrubs, but there is no experimental evidence to support this supposition. *We used compartmentalized microcosms to investigate the R. gardneri tripartite relationship. (13)CO(2) was applied to foliage of Melaleuca scalena plants and [(13)C-(15)N]glycine was fed to the common mycorrhizal fungus, and both sources traced to R. gardneri plants. *In our microcosm trial, up to 5% of carbon (C) fed as (13)CO(2) to the autotrophic shrub was transferred to R. gardneri. R. gardneri also readily acquired soil C and nitrogen (N), where up to 6.2% of C and 22.5% of N fed as labelled glycine to soil was transferred via the fungus to R. gardneri after 240 h. *Our study confirms that R. gardneri is mycoheterotrophic and acquires nutrients via mycorrhizal fungus connections from an ectomycorrhizal autotrophic shrub and directly from the soil via the same fungus. This connection with a specific fungus is key to explaining why R. gardneri occurs exclusively under certain Melaleuca species at a very limited number of sites in Western Australia.
Evolutionary history of mycorrhizal symbioses and global host plant diversity
DOI:10.1111/nph.14976
PMID:29355963
[本文引用: 1]
Contents Summary 1108 I. Introduction 1108 II. Mycorrhizal plant diversity at global and local scales 1108 III. Mycorrhizal evolution in plants: a brief update 1111 IV. Conclusions and perspectives 1114 References 1114 SUMMARY: The majority of vascular plants are mycorrhizal: 72% are arbuscular mycorrhizal (AM), 2.0% are ectomycorrhizal (EcM), 1.5% are ericoid mycorrhizal and 10% are orchid mycorrhizal. Just 8% are completely nonmycorrhizal (NM), whereas 7% have inconsistent NM-AM associations. Most NM and NM-AM plants are nutritional specialists (e.g. carnivores and parasites) or habitat specialists (e.g. hydrophytes and epiphytes). Mycorrhizal associations are consistent in most families, but there are exceptions with complex roots (e.g. both EcM and AM). We recognize three waves of mycorrhizal evolution, starting with AM in early land plants, continuing in the Cretaceous with multiple new NM or EcM linages, ericoid and orchid mycorrhizas. The third wave, which is recent and ongoing, has resulted in root complexity linked to rapid plant diversification in biodiversity hotspots.© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.
Mutualistic mycorrhiza in orchids: evidence from plant-fungus carbon and nitrogen transfers in the green-leaved terrestrial orchid Goodyera repens
DOI:10.1111/j.1469-8137.2006.01767.x
PMID:16866946
[本文引用: 2]
The roles of mycorrhiza in facilitating the acquisition and transfer of carbon (C) and nitrogen (N) to adult orchids are poorly understood. Here, we employed isotopically labelled sources of C and N to investigate these processes in the green forest orchid, Goodyera repens. Fungus-to-orchid transfers of C and N were measured using mass spectrometry after supplying extraradical mycelial systems with double-labelled [13C-15N]glycine. Orchid-to-fungus C transfer was revealed and quantified by radioisotope imaging and liquid scintillation counting of extraradical mycelium following 14CO2 fixation by shoots. Both 13C and 15N were assimilated by the fungus and transferred to the roots and shoots of the orchid. Contrary to previous reports, considerable quantities (2.6% over 72 h) of fixed C were shown to be allocated to the extraradical mycelium of the fungus. This study demonstrates, for the first time, mutualism in orchid mycorrhiza, bidirectional transfer of C between a green orchid and its fungal symbiont, and a fungus-dependent pathway for organic N acquisition by an orchid.
A phylogenetic analysis of the Orchidaceae: evidence from rbcL nucleotide sequences
Cladistic parsimony analyses of rbcL nucleotide sequence data from 171 taxa representing nearly all tribes and subtribes of Orchidaceae are presented here. These analyses divide the family into five primary monophyletic clades: apostasioid, cypripedioid, vanilloid, orchidoid, and epidendroid orchids, arranged in that order. These clades, with the exception of the vanilloids, essentially correspond to currently recognized subfamilies. A distinct subfamily, based upon tribe Vanilleae, is supported for Vanilla and its allies. The general tree topology is, for the most part, congruent with previously published hypotheses of intrafamilial relationships; however, there is no evidence supporting the previously recognized subfamilies Spiranthoideae, Neottioideae, or Vandoideae. Subfamily Spiranthoideae is embedded within a single clade containing members of Orchidoideae and sister to tribe Diurideae. Genera representing tribe Tropideae are placed within the epidendroid clade. Most traditional subtribal units are supported within each clade, but few tribes, as currently circumscribed, are monophyletic. Although powerful in assessing monophyly of clades within the family, in this case rbcL fails to provide strong support for the interrelationships of the subfamilies (i.e., along the spine of the tree). The cladograms presented here should serve as a standard to which future morphological and molecular studies can be compared.
An updated classification of Orchidaceae
DOI:10.1111/boj.12234 URL [本文引用: 1]
Dynamics of fungal communities during Gastrodia elata growth
DOI:10.1186/s12866-019-1501-z
PMID:31291888
[本文引用: 1]
Gastrodia elata is a widely distributed achlorophyllous orchid and is highly valued as both medicine and food. Gastrodia elata produces dust-like seeds and relies on mycorrhizal fungi for its germination and growth. In its life cycle, G. elata is considered to switch from a specific single-fungus relationship (Mycena) to another single-fungus relationship (Armillaria). However, no studies have investigated the changes in the plant-fungus relationship during the growth of G. elata in the wild. In this study, high-throughput sequencing was used to characterize the fungal community of tubers in different growth phases as well as the soils surrounding G. elata.The predominant fungi were Basidiomycota (60.44%) and Ascomycota (26.40%), which exhibited changes in abundance and diversity with the growth phases of G. elata. Diverse basidiomycetes in protocorms (phase P) were Hyphodontia, Sistotrema, Tricholoma, Mingxiaea, Russula, and Mycena, but the community changed from a large proportion of Resinicium bicolor (40%) in rice-like tubers (phase M) to an unidentified Agaricales operational taxonomic unit 1(OTU1,98.45%) in propagation vegetation tubers (phase B). The soil fungi primarily included Simocybe, Psathyrella, Conocybe, and Subulicystidium. Three Mycena OTUs obtained in this study were differentially distributed among the growth phases of G. elata, accounting for less than 1.0% of the total reads, and were phylogenetically close to Mycena epipterygia and M. alexandri.Our data indicated that G. elata interacts with a broad range of fungi beyond the Mycena genus. These fungi changed with the growth phases of G. elata. In addition, these data suggested that the development of the fungal community during the growth of G. elata was more complex than previously assumed and that at least two different fungi could be involved in development before the arrival of Armillaria.
The number of known plants species in the world and its annual increase
DOI:10.11646/phytotaxa.261.3.1 URL [本文引用: 1]
The fungal endophytes of Erythrorchis cassythoides—Is this orchid saprophytic or parasitic
Nitrogen transport in the orchid mycorrhizal symbiosis—Further evidence for a mutualistic association
DOI:10.1111/nph.14357 PMID:27891646 [本文引用: 1]
Orchid mycorrhizas: molecular ecology, physiology, evolution and conservation aspects
//Hock B.
Fungal and plant gene expression in the Tulasnella calospora-Serapias vomeracea symbiosis provides clues about nitrogen pathways in orchid mycorrhizas
DOI:10.1111/nph.14279 URL [本文引用: 3]
Cell-specific expression of plant nutrient transporter genes in orchid mycorrhizae
DOI:10.1016/j.plantsci.2017.06.015 URL [本文引用: 3]
Nitrogen isotope ratios in different compartments of a mixed stand of spruce, larch and beech trees and of understorey vegetation including fungi
15N and 13C natural abundance of autotrophic and myco-heterotrophic orchids provides insight into nitrogen and carbon gain from fungal association
DOI:10.1046/j.1469-8137.2003.00872.x
PMID:33873535
[本文引用: 16]
• Whereas mycorrhizal fungi are acknowledged to be the sources of nitrogen (N) and carbon (C) in achlorophyllous (myco-heterotrophic) orchids, the sources of these elements in autotrophic orchids are unknown. We have determined the stable isotope abundance of N and C to quantify their gain from different sources in these two functional groups and in non-orchids of distinctive mycorrhizal types. • Leaves of each plant were collected from four forest and four grassland sites in Europe. The N and C isotope abundance, and total N concentrations of their tissues and of associated soils were determined. • Myco-heterotrophic orchids were significantly more enriched in N (ɛ = 11.5‰) and C (ɛ = 8.4‰) than co-occurring non-orchids. δ N and δ C signatures of autotrophic orchids ranged from values typical of non-orchids to those more representative of myco-heterotrophic orchids. • Utilization of fungi-derived N and C probably explains the relative N and C enrichment in the myco-heterotrophs. A linear two-source isotopic mixing model was used to estimate N and C gain of autotrophic orchids from their fungal associates. Of the putatively autotrophic species, Cephalanthera damasonium obtained the most N and C by the fungal route, but several other species also fell into the partially myco-heterotrophic category.
Studies on the cell ultrastructure in the course of Gastrodia elata digesting Mycena osmundicola Lange and Armillaria mellea Fr
天麻消化紫萁小菇及蜜环菌过程中细胞超微结构变化研究
Comparative study of key phosphorus and nitrogen metabolizing enzymes in mycorrhizal and non-mycorrhizal plants of Dendrobium chrysanthum Wall. ex Lindl
DOI:10.1007/s11738-013-1268-z URL [本文引用: 1]
Generalism in the interaction of Tulasnellaceae mycobionts with orchids characterizes a biodiversity hotspot in the tropical Andes of Southern Ecuador
DOI:10.1016/j.myc.2017.08.003 URL [本文引用: 1]
Foliar and fungal 15N:14N ratios reflect development of mycorrhizae and nitrogen supply during primary succession: testing analytical models
Nitrogen isotopes (15N/14N ratios, expressed as delta15N values) are useful markers of the mycorrhizal role in plant nitrogen supply because discrimination against 15N during creation of transfer compounds within mycorrhizal fungi decreases the 15N/14N in plants (low delta15N) and increases the 15N/14N of the fungi (high delta15N). Analytical models of 15N distribution would be helpful in interpreting delta15N patterns in fungi and plants. To compare different analytical models, we measured nitrogen isotope patterns in soils, saprotrophic fungi, ectomycorrhizal fungi, and plants with different mycorrhizal habits on a glacier foreland exposed during the last 100 years of glacial retreat and on adjacent non-glaciated terrain. Since plants during early primary succession may have only limited access to propagules of mycorrhizal fungi, we hypothesized that mycorrhizal plants would initially be similar to nonmycorrhizal plants in delta15N and then decrease, if mycorrhizal colonization were an important factor influencing plant delta15N. As hypothesized, plants with different mycorrhizal habits initially showed similar delta15N values (-4 to -6 per thousand relative to the standard of atmospheric N2 at 0 per thousand), corresponding to low mycorrhizal colonization in all plant species and an absence of ectomycorrhizal sporocarps. In later successional stages where ectomycorrhizal sporocarps were present, most ectomycorrhizal and ericoid mycorrhizal plants declined by 5-6 per thousand in delta15N, suggesting transfer of 15N-depleted N from fungi to plants. The values recorded (-8 to -11 per thousand) are among the lowest yet observed in vascular plants. In contrast, the delta15N of nonmycorrhizal plants and arbuscular mycorrhizal plants declined only slightly or not at all. On the forefront, most ectomycorrhizal and saprotrophic fungi were similar in delta15N (-1 to -3 per thousand), but the host-specific ectomycorrhizal fungus Cortinarius tenebricus had values of up to 7 per thousand. Plants, fungi and soil were at least 4 per thousand higher in delta15N from the mature site than in recently exposed sites. On both the forefront and the mature site, host-specific ectomycorrhizal fungi had higher delta15N values than ectomycorrhizal fungi with a broad host range. From these isotopic patterns, we conclude: (1) large enrichments in 15N of many ectomycorrhizal fungi relative to co-occurring ectomycorrhizal plants are best explained by treating the plant-fungal-soil system as a closed system with a discrimination against 15N of 8-10 per thousand during transfer from fungi to plants, (2) based on models of 15N mass balance, ericoid and ectomycorrhizal fungi retain up to two-thirds of the N in the plant-mycorrhizal system under the N-limited conditions at forefront sites, (3) sporocarps are probably enriched in 15N by an additional 3 per thousand relative to available nitrogen, and (4) host-specific ectomycorrhizal fungi may transfer more N to plant hosts than non-host-specific ectomycorrhizal fungi. Our study confirms that nitrogen isotopes are a powerful tool for probing nitrogen dynamics between mycorrhizal fungi and associated plants.
Fungal hosts for mycoheterotrophic plants: a nonexclusive, but highly selective club
DOI:10.1111/j.1469-8137.2009.03152.x URL [本文引用: 3]
The physiological ecology of mycoheterotrophy
//Merckx VSFT.
Plant family identity distinguishes patterns of carbon and nitrogen stable isotope abundance and nitrogen concentration in mycoheterotrophic plants associated with ectomycorrhizal fungi
DOI:10.1093/aob/mcw119 URL [本文引用: 21]
Mycorrhizal symbioses and the evolution of trophic modes in plants
DOI:10.1111/1365-2745.13165
[本文引用: 1]
Since the early colonization of land, plants depend, to various extents, on mycorrhizal fungi to meet their nutrient demands. In most mycorrhizal symbioses, plants provide sugars derived from photosynthesis to the fungi, whereas the fungi provide essential minerals to the plant. However, in some plants, the flow of carbon has reversed and the fungi provide carbon to the plants. These plants are called mycoheterotrophs. However, it remains unclear how and under which circumstances trophic modes change and whether transitions in trophic modes are associated with changes in mycorrhizal communities. Here, we review the available literature on mycorrhizal associations and trophic modes in plants. We first outline how trophic modes can be determined and how they differ across plants. We then investigate the evolutionary context under which mycoheterotrophy originated. We also examine the mycorrhizal communities associating with autotrophic, partially mycoheterotrophic and fully mycoheterotrophic plants within different plant families and investigate whether commonalities can be observed. Our overview shows that mycoheterotrophy has originated more than 40 times through evolutionary time and can be found in a wide range of plant groups, including liverworts, lycophytes, ferns, monocots and dicots. Partial mycoheterotrophy appears to be much more common than previously anticipated and represents an almost continuous gradient between autotrophy and full mycoheterotrophy. Comparison of the mycorrhizal communities associating with autotrophic, partial and full mycoheterotrophic plants indicates that, although they share some commonalities, shifts from autotrophy to full mycoheterotrophy are accompanied by either losses or shifts in mycorrhizal partners, suggesting that full or partial loss of photosynthesis selects for different mycorrhizal communities. Synthesis. Partial mycoheterotrophy appears to be much more common than previously thought and represents an almost continuous gradient from autotrophy to full mycoheterotrophy. Evolution to full mycoheterotrophy is challenging as it requires specific adaptations and often a switch to other mycorrhizal partners. More detailed analyses of the functionality of different mycorrhizal systems co-occurring in the roots of a single plant and the costs of mycorrhizal switching are needed to understand the precise mechanisms leading to full mycoheterotrophy.
Stable isotope cellular imaging reveals that both live and degenerating fungal pelotons transfer carbon and nitrogen to orchid protocorms
DOI:10.1111/nph.12700 URL [本文引用: 3]
Gastrodia elata and its symbiotic association with Armillaria mellea
The biology of myco-heterotrophic (‘saprophytic’) plants
DOI:10.1111/j.1469-8137.1994.tb04272.x URL [本文引用: 1]
Physiological ecology of mycoheterotrophy
DOI:10.1111/j.1469-8137.2009.03153.x URL [本文引用: 5]
The importance of associations with saprotrophic non-rhizoctonia fungi among fully mycoheterotrophic orchids is currently under- estimated: novel evidence from sub-tropical Asia
DOI:10.1093/aob/mcv085 URL [本文引用: 12]
Stable isotope signatures confirm carbon and nitrogen gain through ectomycorrhizas in the ghost orchid Epipogium aphyllum Swartz
DOI:10.1111/j.1438-8677.2010.00369.x
PMID:21309973
[本文引用: 6]
Epipogium aphyllum is a rare Eurasian achlorophyllous forest orchid known to associate with fungi that form ectomycorrhizas, while closely related orchids of warm humid climates depend on wood- or litter-decomposer fungi. We conducted (13) C and (15) N stable isotope natural abundance analyses to identify the organic nutrient source of E. aphyllum from Central Norway. These data for orchid shoot tissues, in comparison to accompanying autotrophic plants, document C and N flow from ectomycorrhizal fungi to the orchid. DNA data from fungal pelotons in the orchid root cortex confirm the presence of Inocybe and Hebeloma, which are both fungi that form ectomycorrhizas. The enrichment factors for (13) C and (15) N of E. aphyllum are used to calculate a new overall average enrichment factor for mycoheterotrophic plants living in association with ectomycorrhizal fungi (ε(13) C ± 1 SD of 7.2 ± 1.6 ‰ and ε(15) N ± 1 SD of 12.8 ± 3.9 ‰). These can be used to estimate the fungal contribution to organic nutrient uptake by partially mycoheterotrophic plants where fully mycoheterotrophic plants are lacking. N concentrations in orchid tissue were unusually high and significantly higher than in accompanying autotrophic leaf samples. This may be caused by N gain of E. aphyllum from obligate ectomycorrhizal fungi. We show that E. aphyllum is an epiparasitic mycoheterotrophic orchid that depends on ectomycorrhizal Inocybe and Hebeloma to obtain C and N through a tripartite system linking mycoheterotrophic plants through fungi with forest trees.© 2010 German Botanical Society and The Royal Botanical Society of the Netherlands.
Independent recruitment of saprotrophic fungi as mycorrhizal partners by tropical achlorophyllous orchids
DOI:10.1111/j.1469-8137.2009.02987.x URL [本文引用: 8]
The role of epiphytism in architecture and evolutionary constraint within mycorrhizal networks of tropical orchids
DOI:10.1111/j.1365-294X.2012.05692.x URL [本文引用: 3]
Symbiotic germination and development of the myco-heterotrophic orchid Neottia nidus-avis in nature and its requirement for locally distributed Sebacina spp.
DOI:10.1046/j.1469-8137.2002.00372.x URL [本文引用: 1]
Mycoheterotrophy:an introduction
// Merckx VSFT.
Mycoheterotrophy evolved from mixotrophic ancestors: evidence in Cymbidium (Orchidaceae)
DOI:10.1093/aob/mcq156 URL [本文引用: 13]
Evidence for novel and specialized mycorrhizal parasitism:the orchid Gastrodia confusa gains carbon from saprotrophic Mycena
The giant mycoheterotrophic orchid Erythrorchis altissima is associated mainly with a divergent set of wood-decaying fungi
DOI:10.1111/mec.14524
PMID:29419910
[本文引用: 3]
The climbing orchid Erythrorchis altissima is the largest mycoheterotroph in the world. Although previous in vitro work suggests that E. altissima has a unique symbiosis with wood-decaying fungi, little is known about how this giant orchid meets its carbon and nutrient demands exclusively via mycorrhizal fungi. In this study, the mycorrhizal fungi of E. altissima were molecularly identified using root samples from 26 individuals. Furthermore, in vitro symbiotic germination with five fungi and stable isotope compositions in five E. altissima at one site were examined. In total, 37 fungal operational taxonomic units (OTUs) belonging to nine orders in Basidiomycota were identified from the orchid roots. Most of the fungal OTUs were wood-decaying fungi, but underground roots had ectomycorrhizal Russula. Two fungal isolates from mycorrhizal roots induced seed germination and subsequent seedling development in vitro. Measurement of carbon and nitrogen stable isotope abundances revealed that E. altissima is a full mycoheterotroph whose carbon originates mainly from wood-decaying fungi. All of the results show that E. altissima is associated with a wide range of wood- and soil-inhabiting fungi, the majority of which are wood-decaying taxa. This generalist association enables E. altissima to access a large carbon pool in woody debris and has been key to the evolution of such a large mycoheterotroph.© 2018 John Wiley & Sons Ltd.
High mycorrhizal specificity in a widespread mycoheterotrophic plant, Eulophia zollingeri (Orchidaceae)
DOI:10.3732/ajb.95.1.93
PMID:21632319
[本文引用: 2]
Because mycoheterotrophic plants fully depend on their mycorrhizal partner for their carbon supply, the major limiting factor for the geographic distribution of these plants may be the presence of their mycorrhizal partner. Although this factor may seem to be a disadvantage for increasing geographic distribution, widespread mycoheterotrophic species nonetheless exist. The mechanism causing the wide distribution of some mycoheterotrophic species is, however, seldom discussed. We identified the mycorrhizal partner of a widespread mycoheterotrophic orchid, Eulophia zollingeri, using 12 individuals from seven populations in Japan, Myanmar, and Taiwan by DNA-based methods. All fungal ITS sequences from the roots closely related to those of Psathyrella candolleana (Coprinaceae) from GenBank accessions and herbarium specimens. These results indicate that E. zollingeri is exclusively associated with the P. candolleana species group. Further, the molecular data support the wide distribution and wide-ranging habitat of this fungal partner. Our data provide evidence that a mycoheterotrophic plant can achieve a wide distribution, even though it has a high mycorrhizal specificity, if its fungal partner is widely distributed.
Mycorrhizal diversity and specificity in Lecanorchis (Orchidaceae)
DOI:10.1007/s00572-012-0429-z URL [本文引用: 5]
Fungal endophytes of tree leaves
//Andrews JH, Hirano SS.
Irradiance governs exploitation of fungi: fine-tuning of carbon gain by two partially myco-heterotrophic orchids
DOI:10.1098/rspb.2009.1966 URL [本文引用: 4]
Enzyme secretion by ECM fungi and exploitation of mineral nutrients from soil organic matter
DOI:10.1007/s13595-010-0004-8 URL [本文引用: 1]
Why do mixotrophic plants stay green? A comparison between green orchid individuals in situ
DOI:10.1890/11-2120.1 URL [本文引用: 1]
Two mycoheterotrophic orchids from Thailand tropical dipterocarpacean forests associate with a broad diversity of ectomycorrhizal fungi
DOI:10.1186/1741-7007-7-51 URL [本文引用: 9]
Ectomycorrhizal inocybe species associate with the mycoheterotrophic orchid Epipogium aphyllum but not its asexual propagules
DOI:10.1093/aob/mcn269 URL [本文引用: 4]
You are what you get from your fungi: nitrogen stable isotope patterns in Epipactis species
DOI:10.1093/aob/mcw265
PMID:28334113
[本文引用: 21]
Partially mycoheterotrophic plants are enriched in 13 C and 15 N compared to autotrophic plants. Here, it is hypothesized that the type of mycorrhizal fungi found in orchid roots is responsible for variation in 15 N enrichment of leaf tissue in partially mycoheterotrophic orchids.The genus Epipactis was used as a case study and carbon and nitrogen isotope abundances of eight Epipactis species, fungal sporocarps of four Tuber species and autotrophic references were measured. Mycorrhizal fungi were identified using molecular methods. Stable isotope data of six additional Epipactis taxa and ectomycorrhizal and saprotrophic basidiomycetes were compiled from the literature.The 15 N enrichment of Epipactis species varied between 3·2 ± 0·8 ‰ ( E. gigantea ; rhizoctonia-associated) and 24·6 ± 1·6 ‰ ( E. neglecta ; associated with ectomycorrhizal ascomycetes). Sporocarps of ectomycorrhizal ascomycetes (10·7 ± 2·2 ‰) were significantly more enriched in 15 N than ectomycorrhizal (5·2 ± 4·0 ‰) and saprotrophic basidiomycetes (3·3 ± 2·1 ‰).As hypothesized, it is suggested that the observed gradient in 15 N enrichment of Epipactis species is strongly driven by 15 N abundance of their mycorrhizal fungi; i.e. ɛ 15 N in Epipactis spp. associated with rhizoctonias < ɛ 15 N in Epipactis spp. with ectomycorrhizal basidiomycetes < ɛ 15 N in Epipactis spp. with ectomycorrhizal ascomycetes and basidiomycetes < ɛ 15 N in Epipactis spp. with ectomycorrhizal ascomycetes.© The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com
Exploiting mycorrhizas in broad daylight: partial mycoheterotrophy is a common nutritional strategy in meadow orchids
DOI:10.1111/1365-2745.12831 URL [本文引用: 1]
Stable isotope signatures of underground seedlings reveal the organic matter gained by adult orchids from mycorrhizal fungi
DOI:10.1111/1365-2435.13042 URL [本文引用: 19]
Light limitation and partial mycoheterotrophy in rhizoctonia-associated orchids
DOI:10.1007/s00442-019-04340-0
PMID:30673856
[本文引用: 1]
Partially mycoheterotrophic (PMH) plants obtain organic molecules from their mycorrhizal fungi in addition to carbon (C) fixed by photosynthesis. Some PMH orchids associated with ectomycorrhizal fungi have been shown to flexibly adjust the proportion of organic molecules obtained from fungi according to the habitat's light level. We hypothesise that Neottia ovata and Ophrys insectifera, two orchids associated with saprotrophic rhizoctonia fungi, are also able to increase uptake of organic molecules from fungi as irradiance levels decrease. We continuously measured light availability for individuals of N. ovata and O. insectifera at a grassland and a forest during orchid flowering and fruiting. We repeatedly sampled leaves of N. ovata, O. insectifera and autotrophic reference species for stable isotope natural abundances (δC, δN, δH, δO) and C and N concentrations. We found significant C enrichment in both orchids relative to autotrophic references at the forest but not the grassland, and significant H enrichment at both sites. The C enrichment in O. insectifera was linearly correlated with the habitat's irradiance levels. We conclude that both species can be considered as PMH and at least in O. insectifera, the degree of partial mycoheterotrophy can be fine-tuned according to light availability. However, exploitation of mycorrhizal fungi appears less flexible in saprotroph-associated orchids than in orchids associated with ectomycorrhizal fungi.
Identification of Armillaria nabsnona in Gastrodia Tubers
The latest news from biological interactions in orchids: in love, head to toe.
DOI:10.1111/nph.12769 URL [本文引用: 1]
Chlorophyllous and achlorophyllous specimens of Epipactis microphylla (Neottieae, Orchidaceae) are associated with ectomycorrhizal septomycetes, including truffles
Mycoheterotrophic species (i.e., achlorophyllous plants obtaining carbon from their mycorrhizal fungi) arose many times in evolution of the Neottieae, an orchid tribe growing in forests. Moreover, chlorophyllous Neottieae species show naturally occurring achlorophyllous individuals. We investigated the fungal associates of such a member of the Neottieae, Epipactis microphylla, to understand whether their mycorrhizal fungi predispose the Neottieae to mycoheterotrophy. Root symbionts were identified by sequencing the fungal ITS of 18 individuals from three orchid populations, including achlorophyllous and young, subterranean individuals. No rhizoctonias (the usual orchid symbionts) were recovered, but 78% of investigated root pieces were colonized by Tuber spp. Other Pezizales and some Basidiomycetes were also found. Using electron microscopy, we demonstrated for the first time that ascomycetes, especially truffles, form typical orchid mycorrhizae. All identified fungi (but one) belonged to taxa forming ectomycorrhizae on tree roots, and four of them were even shown to colonize surrounding trees. This is reminiscent of mycoheterotrophic orchid species that also associate with ectomycorrhizal fungi, although with higher specificity. Subterranean and achlorophyllous E. microphylla individuals thus likely rely on tree photosynthates, and a partial mycoheterotrophy in individuals plants can be predicted. We hypothesize that replacement of rhizoctonias by ectomycorrhizal symbionts in Neottieae entails a predisposition to achlorophylly.
The plant growth-promoting fungus MF23 (Mycena sp.) increases production of Dendrobium officinale (Orchidaceae) by affecting nitrogen uptake and NH4+ assimilation
DOI:10.3389/fpls.2021.693561 URL [本文引用: 2]
Carbon and nitrogen gain during the growth of orchid seedlings in nature
DOI:10.1111/nph.12688
PMID:24444001
[本文引用: 10]
For germination and establishment, orchids depend on carbon (C) and nutrients supplied by mycorrhizal fungi. As adults, the majority of orchids then appear to become autotrophic. To compare the proportional C and nitrogen (N) gain from fungi in mycoheterotrophic seedlings and in adults, here we examined in the field C and N stable isotope compositions in seedlings and adults of orchids associated with ectomycorrhizal and saprotrophic fungi. Using a new highly sensitive approach, we measured the isotope compositions of seedlings and adults of four orchid species belonging to different functional groups: fully and partially mycoheterotrophic orchids associated with narrow or broad sets of ectomycorrhizal fungi, and two adult putatively autotrophic orchids associated exclusively with saprotrophic fungi. Seedlings of orchids associated with ectomycorrhizal fungi were enriched in (13) C and (15) N similarly to fully mycoheterotrophic adults. Seedlings of saprotroph-associated orchids were also enriched in (13) C and (15) N, but unexpectedly their enrichment was significantly lower, making them hardly distinguishable from their respective adult stages and neighbouring autotrophic plants. We conclude that partial mycoheterotrophy among saprotroph-associated orchids cannot be identified unequivocally based on C and N isotope compositions alone. Thus, partial mycoheterotrophy may be much more widely distributed among orchids than hitherto assumed. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Evidence for mycorrhizal cheating in Apostasia nipponica, an early-diverging member of the Orchidaceae
DOI:10.1111/nph.17049
PMID:33118174
[本文引用: 2]
Most land plants, from liverworts to angiosperms, form mutualistic mycorrhizal symbioses with fungal partners. However, several plants known as mycoheterotrophs exploit fungal partners by reversing the polarity of carbon movement, which usually moves from plant to fungus. We investigated the physiological ecology of a photosynthetic orchid, Apostasia nipponica, which belongs to the first branching group within the Orchidaceae, to improve our understanding of mycoheterotrophic evolution in orchids. The fungal symbionts and nutrition modes of A. nipponica were investigated using molecular barcoding and carbon-13 ( C) and nitrogen-15 ( N) measurements, respectively. Community profiling based on a metabarcoding technique revealed that A. nipponica associates with specific Ceratobasidium spp. within ectomycorrhizas-forming clades, whereas isotope analysis revealed that A. nipponica was similar to fully mycoheterotrophic orchids in its C signature and was even more enriched in N than most of the fully mycoheterotrophic orchids that exploit ectomycorrhizal fungi. Our molecular and mass-spectrometric approaches demonstrated, for the first time, that a member of the Apostasioideae, the earliest-diverging lineage of the Orchidaceae, gains carbon through both photosynthesis and fungal cheating (i.e. partial mycoheterotrophy) during the adult stage.© 2020 The Authors New Phytologist © 2020 New Phytologist Foundation.
Partial mycoheterotrophy in the leafless orchid Cymbidium macrorhizon
DOI:10.1002/ajb2.1142
PMID:30129024
[本文引用: 1]
The evolution of full mycoheterotrophy is one of the most interesting topics within plant evolution. The leafless orchid Cymbidium macrorhizon is often assumed to be fully mycoheterotrophic even though it has a green stem and fruit capsule. Here, we assessed the trophic status of this species by analyzing the chlorophyll content and the natural C and N abundance in the sprouting and the fruiting season.The chlorophyll content was measured in five sprouting and five fruiting individuals of C. macrorhizon that were co-occurring. In addition, their C and N isotopic signatures were compared with those of neighboring autotrophic and partially mycoheterotrophic reference plants.Fruiting individuals of C. macrorhizon were found to contain a remarkable amount of chlorophyll compared to their sprouting counterparts. In addition, the natural abundance of C in the tissues of the fruiting plants was slightly depleted relative to the sprouting ones. Linear two-source mixing model analysis revealed that fruiting C. macrorhizon plants obtained approximately 73.7 ± 2.0% of their total carbon from their mycorrhizal fungi when the sprouting individuals were used as the 100% carbon gain standard.Our results indicated that despite its leafless status, fruiting plants of C. macrorhizon were capable of fixing significant quantities of carbon. Considering the autotrophic carbon gain increases during the fruiting season, its photosynthetic ability may contribute to fruit and seed production. These results indicate that C. macrorhizon should, therefore, be considered a partially mycoheterotrophic species rather than fully mycoheterotrophic, at least during the fruiting stage.© 2018 Botanical Society of America.
Partial and full mycoheterotrophy in green and albino phenotypes of the slipper orchid Cypripedium debile
DOI:10.1007/s00572-021-01032-7
PMID:33852063
Most green orchids form mycorrhizal associations with rhizoctonia fungi, a polyphyletic group including Serendipitaceae, Ceratobasidiaceae, and Tulasnellaceae. Although accumulating evidence indicated that partial mycoheterotrophy occurs in such so-called rhizoctonia-associated orchids, it remains unclear how much nutrition rhizoctonia-associated orchids obtain via mycoheterotrophic relationships. We investigated the physiological ecology of green and albino individuals of a rhizoctonia-associated orchid Cypripedium debile, by using molecular barcoding of the mycobionts and stable isotope (C and N) analysis. Molecular barcoding of the mycobionts indicated that the green and albino individuals harbored Tulasnella spp., which formed a clade with the previously reported C. debile mycobionts. In addition, stable isotope analysis showed that both phenotypes were significantly enriched in C but not in N. Therefore, green and albino individuals were recognized as partial and full mycoheterotrophs, respectively. The green variants were estimated to obtain 42.5 ± 8.2% of their C from fungal sources, using the C enrichment factor of albino individuals as a mycoheterotrophic endpoint. The proportion of fungal-derived C in green C. debile was higher than that reported in other rhizoctonia-associated orchids. The high fungal dependence may facilitate the emergence of albino mutants. Our study provides the first evidence of partial mycoheterotrophy in the subfamily Cypripedioideae. Partial mycoheterotrophy may be more general than previously recognized in the family Orchidaceae.
Independent, specialized invasions of ectomycorrhizal mutualism by two nonphotosynthetic orchids
We have investigated the mycorrhizal associations of two nonphotosynthetic orchids from distant tribes within the Orchidaceae. The two orchids were found to associate exclusively with two distinct clades of ectomycorrhizal basidiomycetous fungi over wide geographic ranges. Yet both orchids retained the internal mycorrhizal structure typical of photosynthetic orchids that do not associate with ectomycorrhizal fungi. Restriction fragment length polymorphism and sequence analysis of two ribosomal regions along with fungal isolation provided congruent, independent evidence for the identities of the fungal symbionts. All 14 fungal entities that were associated with the orchid Cephalanthera austinae belonged to a clade within the Thelephoraceae, and all 18 fungal entities that were associated with the orchid Corallorhiza maculata fell within the Russulaceae. Restriction fragment length polymorphism and single-strand conformational polymorphism analysis of ectomycorrhizal tree roots collected adjacent to Cephalanthera showed that (i) the fungi associated internally with Cephalanthera also form typical external ectomycorrhizae and that (ii) ectomycorrhizae formed by other Basidiomycetes were abundant where the orchid grows but these fungi did not associate with the orchid. This is the first proof of ectomycorrhizal epiparasitism in nature by an orchid. We argue that these orchids are cheaters because they do not provide fixed carbon to associated fungi. This view suggests that mycorrhizae, like other ancient mutualisms, are susceptible to cheating. The extreme specificity in these orchids relative to other ectomycorrhizal plants agrees with trends seen in more conventional parasites.
Mycorrhizal specificity and function in myco-heterotrophic plants
//van der Heijden MGA, Sanders I.
Parallel evolutionary paths to mycoheterotrophy in understorey Ericaceae and Orchidaceae: ecological evidence for mixotrophy in Pyroleae
Several forest understorey achlorophyllous plants, termed mycoheterotrophs (MHs), obtain C from their mycorrhizal fungi. The latter in turn form ectomycorrhizas with trees, the ultimate C source of the entire system. A similar nutritional strategy occurs in some green forest orchids, phylogenetically close to MH species, that gain their C via a combination of MH and photosynthesis (mixotrophy). In orchid evolution, mixotrophy evolved in shaded habitats and preceded MH nutrition. By generalizing and applying this to Ericaceae, we hypothesized that green forest species phylogenetically close to MHs are mixotrophic. Using stable C isotope analysis with fungi, autotrophic, mixotrophic and MH plants as comparisons, we found the first quantitative evidence for substantial fungi-mediated mixotrophy in the Pyroleae, common ericaceous shrubs from boreal forests close to the MH Monotropoideae. Orthilia secunda, Pyrola chlorantha, Pyrola rotundifolia and Chimaphila umbellata acquired between 10.3 and 67.5% of their C from fungi. High N and 15N contents also suggest that Pyroleae nutrition partly rely on fungi. Examination of root fungal internal transcribed spacer sequences at one site revealed that 39 species of mostly endophytic or ectomycorrhizal fungi, including abundant Tricholoma spp., were associated with O. secunda, P. chlorantha and C. umbellata. These fungi, particularly ectomycorrhizal associates, could thus link mixotrophic Pyroleae spp. to surrounding trees, allowing the C flows deduced from isotopic evidence. These data suggest that we need to reconsider ecological roles of understorey plants, which could influence the dynamics and composition of forest communities.
Spatial repartition and genetic relationship of green and albino individuals in mixed populations of Cephalanthera orchids
DOI:10.1111/j.1438-8677.2009.00252.x
PMID:20636909
[本文引用: 2]
Several green orchids of the Neottieae tribe acquire organic carbon both from their mycorrhizal fungi and from photosynthesis. This strategy may represent an intermediate evolutionary step towards mycoheterotrophy of some non-photosynthetic (albino) orchids. Mixed populations of green and albino individuals possibly represent a transient evolutionary stage offering opportunities to understand the evolution of mycoheterotrophy. In order to understand the emergence of albinos, we investigated patterns of spatial and genetic relationships among green and albino individuals in three mixed populations of Cephalanthera damasonium and one of C. longifolia using spatial repartition and Amplified fragment length polymorphism (AFLP) markers. Two of these populations were monitored over two consecutive flowering seasons. In spatial repartition analyses, albino individuals did not aggregate more than green individuals. Genetic analyses revealed that, in all sampled populations, albino individuals did not represent a unique lineage, and that albinos were often closer related to green individuals than to other albinos from the same population. Genetic and spatial comparison of genets from the 2-year monitoring revealed that: (i) albinos had lower survival than green individuals; (ii) accordingly, albinos detected in the first year did not correspond to the those sampled in the second year; and (iii) with one possible exception, all examined albinos did not belong to any green genet from the same and/or from the previous year, and vice versa. Our results support a scenario of repeated insurgence of the albino phenotypes within the populations, but unsuccessful transition between the two contrasting phenotypes. Future studies should try to unravel the genetic and ecological basis of the two phenotypes.
Nitrogen and carbon stable isotope abundances support the myco- heterotrophic nature and host-specificity of certain achlorophyllous plants
DOI:10.1046/j.1469-8137.2003.00876.x
PMID:33832180
[本文引用: 4]
• Over 400 species of achlorophyllous vascular plants are thought to obtain all C from symbiotic fungi. Consequently, they are termed 'myco-heterotrophic.' However, direct evidence of myco-heterotrophy in these plants is limited. • During an investigation of the patterns of N and C stable isotopes of various ecosystem pools in two old-growth conifer forests, we sampled six species of myco-heterotrophic achlorophyllous plants to determine the ability of stable isotope ratios to provide evidence of myco-heterotrophy and host-specificity within these symbioses. • Dual-isotope signatures of the myco-heterotrophic plants differed from those of all other pools. They were most similar to the signatures of ectomycorrhizal fungi, and least like those of green plants. δ N values of the myco-heterotrophic plants correlated strongly and positively with those of putative mycobionts. • Used in conjunction with other techniques, N and C stable isotope ratios can be used to demonstrate myco-heterotrophy and host-specificity in these plants when other ecosystem pools are well characterized. They also appear promising for estimating the degree of heterotrophy in photosynthetic, partially myco-heterotrophic plants.
Mycorrhizal ecology and evolution: the past, the present, and the future
DOI:10.1111/nph.13288
PMID:25639293
[本文引用: 1]
Almost all land plants form symbiotic associations with mycorrhizal fungi. These below-ground fungi play a key role in terrestrial ecosystems as they regulate nutrient and carbon cycles, and influence soil structure and ecosystem multifunctionality. Up to 80% of plant N and P is provided by mycorrhizal fungi and many plant species depend on these symbionts for growth and survival. Estimates suggest that there are c. 50 000 fungal species that form mycorrhizal associations with c. 250 000 plant species. The development of high-throughput molecular tools has helped us to better understand the biology, evolution, and biodiversity of mycorrhizal associations. Nuclear genome assemblies and gene annotations of 33 mycorrhizal fungal species are now available providing fascinating opportunities to deepen our understanding of the mycorrhizal lifestyle, the metabolic capabilities of these plant symbionts, the molecular dialogue between symbionts, and evolutionary adaptations across a range of mycorrhizal associations. Large-scale molecular surveys have provided novel insights into the diversity, spatial and temporal dynamics of mycorrhizal fungal communities. At the ecological level, network theory makes it possible to analyze interactions between plant-fungal partners as complex underground multi-species networks. Our analysis suggests that nestedness, modularity and specificity of mycorrhizal networks vary and depend on mycorrhizal type. Mechanistic models explaining partner choice, resource exchange, and coevolution in mycorrhizal associations have been developed and are being tested. This review ends with major frontiers for further research.© 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
Evolution of nutritional modes of Ceratobasidiaceae (Cantharellales, Basidiomycota) as revealed from publicly available ITS sequences
DOI:10.1016/j.funeco.2013.03.004 URL [本文引用: 1]
Symbiont switching and trophic mode shifts in Orchidaceae
DOI:10.1111/nph.17414 URL [本文引用: 2]
Effects of nitrogen and phosphorus on plant leaf photosynthesis and carbon partitioning
氮磷对植物光合作用及碳分配的影响
Mycorrhizal fungi promote growth and nitrogen utilization by Dendrobium nobile (Orchidaceae)
菌根真菌促进金钗石斛的生长及氮利用
Sebacinales everywhere: previously overlooked ubiquitous fungal endophytes
DOI:10.1371/journal.pone.0016793 URL [本文引用: 2]
Sebacinales —One thousand and one interactions with land plants
DOI:10.1111/nph.13977 URL [本文引用: 1]
Mycorrhizas alter nitrogen acquisition by the terrestrial orchid Cymbidium goeringii
DOI:10.1093/aob/mct062 URL [本文引用: 1]
The relation between growth of Gastrodia elata protocorms and fungi
天麻原球茎生长发育与紫萁小菇及蜜环菌的关系
Ceratobasidiaceae mycorrhizal fungi isolated from nonphotosynthetic orchid Chamaegastrodia sikokiana
DOI:10.1007/s00572-007-0155-0 URL [本文引用: 1]
Isolation and identification of mycorrhizal fungi associating with an achlorophyllous plant, Epipogium roseum (Orchidaceae)
DOI:10.1007/S10267-004-0218-4 URL [本文引用: 3]
Research advances in Gastrodia elata
天麻的研究进展
Mycorrhizal specificity, preference and plasticity of six slipper orchids from South Western China
DOI:10.1007/s00572-010-0307-5
PMID:20217434
[本文引用: 2]
Mycorrhizal fungi of six endangered species, Paphiopedilum micranthum, Paphiopedilum armeniacum, Paphiopedilum dianthum, Cypripedium flavum, Cypripedium guttatum, and Cypripedium tibeticum, from two closely related genera in the Orchidaceae from Southwestern China, were characterized using the nuclear internal transcribed spacer (ITS) and part of the large subunit gene of mitochondrial rDNA (mtLSU) sequences. The most frequently detected fungi belonged to the Tulasnellaceae. These fungi were represented by 25 ITS sequence types and clustered into seven major clades in the phylogenetic analysis of 5.8S sequences. Species of Paphiopedilum and Cypripedium shared no fungal ITS sequence types in common, but their fungal taxa sometimes occurred in the same major clade of the 5.8S phylogenetic tree. Although it had several associated fungal ITS sequence types in a studied plot, each orchid species had in general only a single dominant type. The fungal sequence type spectra of different species of Paphiopedilum from similar habitats sometimes overlapped; however, the dominant sequence types differed among the species and so did the sequence-type spectra within Cypripedium. Orchids of P. micranthum and P. armeniacum transplanted from the field and grown in two greenhouses had a greater number of mycorrhizal associations than those sampled directly from the field. Root specimens from P. micranthum taken from the greenhouses were preferably associated with mycobionts of the Tulasnella calospora complex, while those from the field had mycorrhizal associations of other tulasnelloid taxa. Such plasticity in mycorrhizal associations makes ex situ conservation or even propagation by means of mycorrhization of axenically grown seedlings possible.
Mycorrhizal diversity in Apostasia (Orchidaceae) indicates the origin and evolution of orchid mycorrhiza
DOI:10.3732/ajb.0900101 URL [本文引用: 2]
Wide geographical and ecological distribution of nitrogen and carbon gains from fungi in pyroloids and monotropoids (Ericaceae) and in orchids
The ectomycorrhizal specialist orchid Corallorhiza trifida is a partial myco- heterotroph
DOI:10.1111/j.1469-8137.2007.02362.x
PMID:18221248
[本文引用: 3]
The leafless, circumboreal orchid Corallorhiza trifida is often assumed to be fully myco-heterotrophic despite contrary evidence concerning its ability to photosynthesize. Here, its level of myco-heterotrophy is assessed by analysing the natural abundance of the stable nitrogen and carbon isotopes (15)N and (13)C, respectively. The mycorrhizal associates and chlorophyll contents of C. trifida were investigated and the C and N isotope signatures of nine C. trifida individuals from Central Europe were compared with those of neighbouring obligate autotrophic and myco-heterotrophic reference plants. The results show that C. trifida only gains c. 52 +/- 5% of its total nitrogen and 77 +/- 10% of the carbon derived from fungi even though it has been shown to specialize on one specific complex of ectomycorrhizal fungi similar to fully myco-heterotrophic orchids. Concurrently, compared with other Corallorhiza species, C. trifida contains a remarkable amount of chlorophyll. Since C. trifida is able to supply significant proportions of its nitrogen and carbon demands through the same processes as autotrophic plants, this species should be referred to as partially myco-heterotrophic.
