四川黄龙沟优势兰科植物菌根真菌多样性及其季节变化

The variations of mycorrhizal fungi diversity among different growing periods of the dominant orchids from two habitats in the Huanglong valley,Sichuan

在自然条件下,兰科菌根真菌对兰花的种子萌发和植株生长都是必不可少的。为了解高原兰科植物菌根真菌的多样性状况及其季节性变化规律,选取了四川黄龙沟的两种生境中生长的8种优势兰科植物,分别于植株的萌芽期(4月份)、生长期(7月份)和果期(9月份)采集营养根进行菌根真菌的多样性研究。其中,黄花杓兰(Cypripedium flavum)、少花鹤顶兰(Phaiusdelavayi)、二叶匍茎兰(Galearis diantha)和广布小蝶兰(Ponerorchis chusua)分布在开阔生境;筒距兰(Tipularia szechuanica)、小花舌唇兰(Platanthera minutiflora)、珊瑚兰(Corallorhiza trifida)和尖唇鸟巢兰(Neottia acuminate)则分布在密林生境。通过对分离所得的50个菌株进行形态观察和ITS序列测定相结合的鉴定,共获得菌根真菌41种。对担子菌和子囊菌分别进行的系统发育树构建结果显示,子囊菌为优势种类(35种),以柔膜菌目(Helotiales)、炭角菌目(Xylariales)和肉座菌目(Hypocreales)内的种类为主,担子菌则以胶膜菌(Tulasnellaceaesp.)为主。在8种兰科植物中,二叶匐茎兰表现出极高的专一性,其菌根真菌均属于Hypocrea。其余兰科植物的菌根真菌分别属于不同的科,专一性相对较低。物种丰富度和Simpson多样性指数分析结果表明,密林生境的兰科植物的菌根真菌多样性在各生长季节基本高于开阔生境。此外,两种生境的优势兰科植物的菌根真菌物种多样性随生长季节转变所呈现的变化规律是相似的:萌发期和生长期的多样性均较高,峰值出现在生长期,到果期时则大幅下降。这与高原兰科植物的生长特性及营养供求规律基本相符。

All orchids have an obligate relationship with mycorrhizal symbionts during seed germination under field conditions,and in many species,the dependency on fungi as a carbohydrate source is prolonged into adulthood.Diversity of orchid mycorrhiza is defined as the species of mycorrhizal fungi compatible with an orchid and the shape of compatibility links between orchids and fungi are referred to as webs.According to traditional records,the majority of mycobiont in terrestrial orchid mycorrhiza belonged in several certain taxonomic groups of basidiomycetes,and there were specific relationships between orchids and fungi.Subsequent studies indicate a more complex situation.The factors which influence the diversity of orchid mycorrhizal fungi is not exactly known.Trophic styles,geographical differences,environmental conditions,or life stages have been reported to play a role in the fungal diversity.Considering the huge temperate zone and alpine mountains,China has rich terrestrial orchid resources.The Huanglong Valley in Sichuan Province,at an elevation of 3100-3569 meter and 3.5kilometers long,is the largest travertine region in the world.Profuse terrestrial orchids from 30 species in 19 genera were found in this narrow valley.Huanglong Valley is one of the temperate terrestrial orchid distribution centers in China.These orchids grew in two different habitats.One was open shrubs with travertine stream flows;another was relative dense mixed coniferous broad-leaved forests without water flows.Cypripedium flavum,Galearis diantha,Ponerorchis chusua and Phaius delavayi were the main orchid species found in open shrub habitat with abundant individuals.Tipularia szechuanica,Platanthera minutiflora,Corallorhiza trifida and Neottia acuminata were the dominant orchid species in forest habitat,the latter two species were myco-heterotrophic,which rely on mycorrhizal fungi throughout their lifetime.From a conservation perspective,this study investigated the diversity of mycorrhizal fungi of temperat wild orchids in the Huanglong Valley,and whether the fungal diversity would vary between different growing periods of orchids,and with the species of host orchids from different habitat.Samples were taken in the different seasons over one year.The mycorrhizal fungi were isolated in tissue blocks cultivation,and identified by using micro structure examination and ITS gene sequence analysis methods.We investigated the diversity of mycorrhizal fungi with species number and Simpson＇s diversity index.The phylogenetic diversity of fungi isolates was also investigated.Forty-one fungi species were isolated from the samples.It was very rare for the eight orchids to share similar species during the same growing period.The molecular phylogeny indicated that the fungi mainly belonged to Helotiales and Hypocreales of Ascomycota,and Tulasnella of Basidiomycota.The Ascomycota was dominant,containing 35 species.Mycorrhizal fungi specificity at the species level was not been found except for Galearis diantha,which was associated with only Hypocrea fungi through out the whole growing season.Species number and Simpson diversity index（D）of mycorrhizal fungi from the orchids growing in a forest habitat were higher than those in a travertine habitat.The variation patterns of mycorrhizal fungi diversity from both habitats were synchronized with the season changing pattern of the Huanglong Vally.The peak of mycorrhizal fungi diversity appeared in the vegetative period,and the minimum value was in the fruiting period.Moreover,the changing pattern of the mycorrhizal fungi diversity between different growing periods was closely associated with the nutrition requirement of the orchids during different growing stages.