Institute of Ecology, School of Life Sciences, Zijingang Campus of Zhejiang University, No 668 of Yuhang Road, Hangzhou, China.
BMC Evol Biol. 2012 Apr 12;12:50. doi: 10.1186/1471-2148-12-50.
Arbuscular mycorrhizal fungi (AMF) can form obligate symbioses with the vast majority of land plants, and AMF distribution patterns have received increasing attention from researchers. At the local scale, the distribution of AMF is well documented. Studies at large scales, however, are limited because intensive sampling is difficult. Here, we used ITS rDNA sequence metadata obtained from public databases to study the distribution of AMF at continental and global scales. We also used these sequence metadata to investigate whether host plant is the main factor that affects the distribution of AMF at large scales.
We defined 305 ITS virtual taxa (ITS-VTs) among all sequences of the Glomeromycota by using a comprehensive maximum likelihood phylogenetic analysis. Each host taxonomic order averaged about 53% specific ITS-VTs, and approximately 60% of the ITS-VTs were host specific. Those ITS-VTs with wide host range showed wide geographic distribution. Most ITS-VTs occurred in only one type of host functional group. The distributions of most ITS-VTs were limited across ecosystem, across continent, across biogeographical realm, and across climatic zone. Non-metric multidimensional scaling analysis (NMDS) showed that AMF community composition differed among functional groups of hosts, and among ecosystem, continent, biogeographical realm, and climatic zone. The Mantel test showed that AMF community composition was significantly correlated with plant community composition among ecosystem, among continent, among biogeographical realm, and among climatic zone. The structural equation modeling (SEM) showed that the effects of ecosystem, continent, biogeographical realm, and climatic zone were mainly indirect on AMF distribution, but plant had strongly direct effects on AMF.
The distribution of AMF as indicated by ITS rDNA sequences showed a pattern of high endemism at large scales. This pattern indicates high specificity of AMF for host at different scales (plant taxonomic order and functional group) and high selectivity from host plants for AMF. The effects of ecosystemic, biogeographical, continental and climatic factors on AMF distribution might be mediated by host plants.
丛枝菌根真菌（AMF）可以与绝大多数陆生植物形成专性共生关系，AMF 的分布模式越来越受到研究人员的关注。在局部尺度上，AMF 的分布已有详细记录。然而，在大尺度上的研究却很有限，因为密集采样很困难。在这里，我们使用从公共数据库中获得的 ITS rDNA 序列元数据来研究 AMF 在大陆和全球尺度上的分布。我们还使用这些序列元数据来研究宿主植物是否是影响 AMF 大尺度分布的主要因素。
我们通过全面的最大似然系统发育分析，定义了所有 Glomeromycota 序列中的 305 个 ITS 虚拟分类单元（ITS-VTs）。每个宿主分类阶元平均约有 53%的特有 ITS-VTs，约 60%的 ITS-VTs 是宿主特异的。那些宿主范围广泛的 ITS-VTs 具有广泛的地理分布。大多数 ITS-VTs 仅出现在一种宿主功能群中。大多数 ITS-VTs 的分布在生态系统、大陆、生物地理区域和气候带中都受到限制。非度量多维标度分析（NMDS）表明，AMF 群落组成在宿主的功能群之间以及在生态系统、大陆、生物地理区域和气候带之间存在差异。Mantel 检验表明，AMF 群落组成与生态系统、大陆、生物地理区域和气候带中的植物群落组成显著相关。结构方程模型（SEM）表明，生态系统、大陆、生物地理区域和气候带对 AMF 分布的影响主要是间接的，而植物对 AMF 有很强的直接影响。
ITS rDNA 序列所指示的 AMF 分布模式在大尺度上表现出高度的特有性。这种模式表明 AMF 在不同尺度（植物分类阶元和功能群）上对宿主具有高度的特异性，并且宿主植物对 AMF 具有高度的选择性。生态系统、生物地理、大陆和气候因素对 AMF 分布的影响可能是由宿主植物介导的。
