| Root-associated fungi(RAF)are termed for soil fungi that grow in,on and out of the plants root system.RAF can be categorized into several functional groups according to their trophic modes,such as symbiotic,saprophytic,and pathogenic types.These functional groups are essential for nutrient cycling and community assembly.Lauraceae and Sapindaceae plants are dominant plant species in the tropical montane rainforest of Hainan Island.Studying the diversity,ecological functions,and interspecific relationships of RAF of Lauraceae and Sapindaceae,and exploring the effects of host plants and spatial factors in shaping the RAF community structuring,will help reveal the species diversity and coexistence mechanisms in tropical forests.In this study,RAF were identified from root tips of plant in family Lauraceae and Sapindaceae dominating the tropical montane rain forest of Jianfengling by molecular analysis of fungal ITS region.RAF diversity,community structure,ecological type,interspecific relationships were characterized.We also probed into questions,such as to what extend the RAF community can be structured by host plants and space.The main findings of this study are as follows:(1)The RAF community was characterized by high diversity that a total of 393 fungal species were detected in this study.At the phylum level,the number of species ranked from high to low were Ascomycota,Basidiomycota,Mucoromycota,and Chytridiomycota,while there are 20 species of RAF that cannot be assigned to a know phylum.At class level,the top five fungal groups with highest number of fungal species were Agaricomycetes,Glomeromycetes,Leotiomycetes,Sordariomycetes and Dothideomycetes.215 species can be assign to a known order,with Glomerales,Agaricales,Helotiales,Russulales and Chaetothyriales are the most species rich groups.RAF community are well represented by fungi from family Glomeraceae,Russulaceae and Hyaloscyphaceae.Only 58 RAF species could be assigned to fungal genera,with Rhizophagus was the most abundant species,followed by Glomus,Mortierella and Russula.(2)Trophic mode of the RAF was varied,with 122 out of the 393 RAF can be assign to a given functional group,eg.,symbiotroph,saprotroph,pathotroph,pathotroph-saprotroph,and pathotroph-saprotroph-symbiotroph.Symbiotic fungi,being represented by the AM fungi,have the highest number of species(68).(3)There were significant differences in the species composition of RAF community between Lauraceae and Sapindaceae plants.In general,the AMF prefers Lauraceae plants,while Ascomycota and Basidiomycota tend to associated with plants in Sapindaceae,but limited portions of variations in RAF community composition was explained by plant identity.(4)Spatial autocorrelation on RAF and AMF species composition were detected at the distance of 6-14 m,whereas no effect was found at larger distance scale,29 m.Plot based Mantel tests indicated that,spatial structure of RAF and AMF are not constant,that 3 out of 5 plots showed significant spatial autocorrelation at distances of 6.6 m,13.8 m,or 28.6 m,while the other two plots did not show distinct distance effects.PCNM analysis shows spatial factors only has little influence on RAF community composition at lager scale.(5)The RAF community of Lauraceae and Sapindaceae are featured by a competitive relationship that the observed C-scores were significantly higher than the value predicted by null model.Co-ocurrence analysis carried out for different fungal group,i.e.,AMF,ectomycorrhizal fungi,and saprophytic fungi communities are all showed competitive relationships,while interspecific relationship between pathogenic fungi were randomly arranged.These findings suggest that competition is an important mechanism for RAF community assemblage in tropical montane rain forest of Hainan Island. |
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