Institute of Ecology and Earth Sciences and Natural History Museum of Tartu University, 40 Lai Street, 51005, Tartu, Estonia.
Mycorrhiza. 2010 Apr;20(4):217-63. doi: 10.1007/s00572-009-0274-x. Epub 2009 Sep 16.
The ectomycorrhizal (EcM) symbiosis involves a large number of plant and fungal taxa worldwide. During studies on EcM diversity, numerous misidentifications, and contradictory reports on EcM status have been published. This review aims to: (1) critically assess the current knowledge of the fungi involved in the EcM by integrating data from axenic synthesis trials, anatomical, molecular, and isotope studies; (2) group these taxa into monophyletic lineages based on molecular sequence data and published phylogenies; (3) investigate the trophic status of sister taxa to EcM lineages; (4) highlight other potentially EcM taxa that lack both information on EcM status and DNA sequence data; (5) recover the main distribution patterns of the EcM fungal lineages in the world. Based on critically examining original reports, EcM lifestyle is proven in 162 fungal genera that are supplemented by two genera based on isotopic evidence and 52 genera based on phylogenetic data. Additionally, 33 genera are highlighted as potentially EcM based on habitat, although their EcM records and DNA sequence data are lacking. Molecular phylogenetic and identification studies suggest that EcM symbiosis has arisen independently and persisted at least 66 times in fungi, in the Basidiomycota, Ascomycota, and Zygomycota. The orders Pezizales, Agaricales, Helotiales, Boletales, and Cantharellales include the largest number of EcM fungal lineages. Regular updates of the EcM lineages and genera therein can be found at the UNITE homepage http://unite.ut.ee/EcM_lineages . The vast majority of EcM fungi evolved from humus and wood saprotrophic ancestors without any obvious reversals. Herbarium records from 11 major biogeographic regions revealed three main patterns in distribution of EcM lineages: (1) Austral; (2) Panglobal; (3) Holarctic (with or without some reports from the Austral or tropical realms). The holarctic regions host the largest number of EcM lineages; none are restricted to a tropical distribution with Dipterocarpaceae and Caesalpiniaceae hosts. We caution that EcM-dominated habitats and hosts in South America, Southeast Asia, Africa, and Australia remain undersampled relative to the north temperate regions. In conclusion, EcM fungi are phylogenetically highly diverse, and molecular surveys particularly in tropical and south temperate habitats are likely to supplement to the present figures. Due to great risk of contamination, future reports on EcM status of previously unstudied taxa should integrate molecular identification tools with axenic synthesis experiments, detailed morphological descriptions, and/or stable isotope investigations. We believe that the introduced lineage concept facilitates design of biogeographical studies and improves our understanding about phylogenetic structure of EcM fungal communities.
外生菌根（EcM）共生关系涉及全球大量的植物和真菌类群。在研究 EcM 多样性的过程中，已经发表了许多关于 EcM 状态的错误鉴定和相互矛盾的报告。本综述旨在：（1）通过整合来自无菌合成试验、解剖学、分子和同位素研究的数据，批判性地评估参与 EcM 的真菌的当前知识；（2）根据分子序列数据和已发表的系统发育将这些分类群分为单系谱系；（3）调查与 EcM 谱系姐妹分类群的营养状态；（4）强调其他缺乏 EcM 状态信息和 DNA 序列数据的潜在 EcM 分类群；（5）恢复 EcM 真菌谱系在世界上的主要分布模式。基于对原始报告的批判性检查，证明了 162 个真菌属具有外生菌根生活方式，其中两个属基于同位素证据补充，52 个属基于系统发育数据补充。此外，基于生境，有 33 个属被突出为潜在的 EcM，尽管它们缺乏 EcM 记录和 DNA 序列数据。分子系统发育和鉴定研究表明，EcM 共生关系在真菌中至少独立出现并持续存在了 66 次，在担子菌门、子囊菌门和接合菌门中。Pezizales、Agaricales、Helotiales、Boletales 和 Cantharellales 目包含最大数量的 EcM 真菌谱系。EcM 谱系及其分类群的最新信息可在 UNITE 主页 http://unite.ut.ee/EcM_lineages 上找到。大多数 EcM 真菌是从腐殖质和木材腐生祖先进化而来的，没有明显的逆转。来自 11 个主要生物地理区域的标本记录揭示了 EcM 谱系分布的三种主要模式：（1）澳大拉西亚；（2）泛全球；（3）全北极（有或没有来自澳大拉西亚或热带地区的一些报告）。全北极地区拥有最多的 EcM 谱系；没有一个热带分布仅限于豆科和苏木科的宿主。我们警告说，与北温带地区相比，南美的外生菌根主导栖息地和宿主、东南亚、非洲和澳大利亚的外生菌根主导栖息地和宿主仍然未被充分采样。总之，外生菌根真菌在系统发育上具有高度多样性，特别是在热带和南温带生境中的分子调查很可能会补充现有数据。由于存在很大的污染风险，未来关于以前未研究分类群 EcM 状态的报告应将分子鉴定工具与无菌合成实验、详细的形态描述和/或稳定同位素研究相结合。我们相信，引入的谱系概念有助于设计生物地理研究，并提高我们对外生菌根真菌群落系统发育结构的理解。
