Abstract
Root-associated fungi, including ectomycorrhizal and root-endophytic fungi, are among the most diverse and important belowground plant symbionts in dipterocarp rainforests. Our study aimed to reveal the biodiversity, host association, and community structure of ectomycorrhizal Basidiomycota and root-associated Ascomycota (including root-endophytic Ascomycota) in a lowland dipterocarp rainforest in Southeast Asia. The host plant chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) region and fungal internal transcribed spacer 2 (ITS2) region were sequenced using tag-encoded, massively parallel 454 pyrosequencing to identify host plant and root-associated fungal taxa in root samples. In total, 1245 ascomycetous and 127 putative ectomycorrhizal basidiomycetous taxa were detected from 442 root samples. The putative ectomycorrhizal Basidiomycota were likely to be associated with closely related dipterocarp taxa to greater or lesser extents, whereas host association patterns of the root-associated Ascomycota were much less distinct. The community structure of the putative ectomycorrhizal Basidiomycota was possibly more influenced by host genetic distances than was that of the root-associated Ascomycota. This study also indicated that in dipterocarp rainforests, root-associated Ascomycota were characterized by high biodiversity and indistinct host association patterns, whereas ectomycorrhizal Basidiomycota showed less biodiversity and a strong host phylogenetic preference for dipterocarp trees. Our findings lead to the working hypothesis that root-associated Ascomycota, which might be mainly represented by root-endophytic fungi, have biodiversity hotspots in the tropics, whereas biodiversity of ectomycorrhizal Basidiomycota increases with host genetic diversity.
Highlights
Plants harbor an array of mutualistic and antagonistic fungi in their root system and rhizosphere, including mycorrhizal, endophytic, litter decomposing, and plant pathogenic fungi [1,2,3]
Of the 148 plant operational taxonomic unit (OTU), 90.3% were identified to the family level, S6 Dataset, S1 Fig. Among the potential ECM host lineages in the plot, Dipterocarpaceae were the most common (183/ 399, or 45.9% of total samples); Fagaceae were not detected in our samples
Our results revealed that tropical trees in the Lambir Hills National Park host a large number of Dikarya OTUs in their root systems
Summary
Plants harbor an array of mutualistic and antagonistic fungi in their root system and rhizosphere, including mycorrhizal, endophytic, litter decomposing, and plant pathogenic fungi [1,2,3]. Root-associated fungi ubiquitously interact with plants as commensalistic, parasitic and mutualistic symbionts, representing the unseen majority of microbes in root systems and rhizospheres in terrestrial ecosystems [4,5,6]. They facilitate plant growth and health, maintenance of plant diversity, nutrient cycling, and ecosystem productivity in various forest and grassland habitats [7,8,9,10,11]. Mycorrhizal fungi are one of the most important types of plant symbionts in root systems and the rhizosphere. A relatively small number of plant taxa form ECM (e.g., Fagaceae, Betulaceae, Salicaceae, Dipterocarpaceae, Myrtaceae, and Pinaceae; [15]), the importance of ECM fungi is widely recognized because ECM plants dominate various types of temperate and tropical forests [16,17,18,19,20]
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