美国山核桃的外生菌根真菌多样性及分布格局研究

Pecan trees (Carya illinoiensis) are ectomycorrhizal, and have been introduced and planted widely in China for commercial nuts. However, the success rate of the seedlings transplanting in China is lower than 50%, while no study has yet addressed the degree to which fungal partners are maintained in pecan orchards in China, or new associations, are formed with pecan trees outside of their native range. Aims to screen fungal strains applicable to the seedlings production based on the investigation of ectomycorrhizal fungal (EMF) diversity, as well as to investigate the EMF community turn over along environmental factors, this study will apply next generation sequencing methods to assess EMF communities colonizing pecan trees within orchards across China at regional-scale, and measure soil factors that may alter the fungal communities. Incorporating with previous data generated from the native area in North America, the mechanism of how pecan trees recruit ectomycorrhizal fungi from areas outside of its native area to adapt to new environments will also be investigated. This study will contribute to the understanding of how ectomycorrhizal host trees adopt to new environment, and the diversity of ectomycorrhizal fungi associated with pecan trees with new and endemic species added. Besides, promising fungal strains applicable to the pecan seedling productions will be proposed based on the development of the database on fungi associated with pecan trees.

美国山核桃已引种至我国100多年，近年正在全国大面积推广，是发展果木-食用菌立体经济的理想树种。但生产上幼苗菌根化程度低，移栽成活率不到50%。合成菌根菌剂并应用于生产是提高其成活率的关键，但人们对引种的美国山核桃的外生菌根真菌(EMF)多样性及其如何招募EMF以适应新环境的机制知之甚少。项目组前期研究发现：引种的美国山核桃能与多个中国的土著真菌共生，其EMF群落组成可能已与其原产地的不同，发生了转换。本研究拟对引种的美国山核桃进行系统的取样和调查，结合形态学、Illumina测序鉴定及多元统计分析，对其EMF进行研究，旨在：①深入认识美国山核桃的EMF多样性、区域和洲际分布格局及群落变化规律；②阐明影响美国山核桃EMF群落的主要环境因子，探讨其在中国的生态适应性机制；③建立完善的EMF数据库，挖掘出既有助于美国山核桃菌根化又具重要经济价值的EMF资源，为果木-食用菌立体经营提供科学依据。

美国山核桃具有重要的生态和经济价值，已引种至我国多年，但人们对其外生菌根真菌的多样性和群落组成还知之甚少。项目组通过对分布于云南、贵州、四川、湖南、湖北、浙江、安徽等地的美国山核桃种植园进行了广泛采集，结合形态学观察和ITS高通量测序，对美国山核桃的外生菌根真菌进行了分子鉴定和群落结构研究。研究结果表明：在中国，能与美国山核桃形成外生菌根的真菌颇为丰富，包括子囊菌门和担子菌门的15个演化支系的81个可操作分类单元（operational taxonomic units, OTUs）。在这81个ECM真菌中，有3个OTUs在美国山核桃、云南松、壳斗科植物样品中都有检测到，8个在在美国山核桃和壳斗科植物样品中同时检测到，15个OTUs在美国山核桃和云南松样品中同时检测到，只在美国山核桃中检测到的OTUs有55个。中国和美国的美国山核桃园中的外生菌根真菌在科、属水平上差异不明显，但在OTUs水平上差异明显。中、美两地与美国山核桃共生真菌表现出明显的物种替换，两地具有不同的外生菌根真菌区系组成及两地在空间上对菌根真菌的传播限制可能是导致明显的物种替换之源。本研究建立了美国山核桃外生菌根真菌数据库，筛选出了会东块菌Tuber huidongense、印度块菌Tuber indicum在等具有较高的商业价值的外生菌根真菌作为美国山核桃菌根合成的重要候选物种。研究结果对美国山核桃的幼苗培育和山核桃-食用菌立体经营具有重要参考价值。