Ericaceous plant–fungus network in a harsh alpine–subalpine environment

Abstract

In terrestrial ecosystems, plant species and diverse root-associated fungi form complex networks of host-symbiont associations. Recent studies have revealed that structures of those below-ground plant-fungus networks differ between arbuscular mycorrhizal and ectomycorrhizal symbioses. Nonetheless, we still remain ignorant of how ericaceous plant species, which dominate arctic and alpine tundra, constitute networks with their root-associated fungi. Based on a high-throughput DNA sequencing data set, we characterized the statistical properties of a network involving 16 ericaceous plant species and more than 500 fungal taxa in the alpine-subalpine region of Mt. Tateyama, central Japan. While all the 16 ericaceous species were associated mainly with fungi in the order Helotiales, they varied remarkably in association with fungi in other orders such as Sebacinales, Atheliales, Agaricales, Russulales and Thelephorales. The ericaceous plant-fungus network was characterized by high symbiont/host preferences. Moreover, the network had a characteristic structure called 'anti-nestedness', which has been previously reported in ectomycorrhizal plant-fungus networks. The results lead to the hypothesis that ericaceous plants in harsh environments can host unexpectedly diverse root-associated fungal taxa, constituting networks whose structures are similar to those of previously reported ectomycorrhizal networks but not to those of arbuscular mycorrhizal ones.

Networks Depicting the Fine-Scale Co-Occurrences of Fungi in Soil Horizons

“…In general, DNA-barcoding-based analyses do not provide any direct evidences of niche differentiation or interspecific interactions [10, 42, 43]. Therefore, our aim was not revealing “common mycelial networks” linking fungal (and host plant) individuals/species [5, 44] but detecting sings of potential niche differentiation and interspecific interactions [42, 43]. Throughout this paper, we use the term “network” in a broad sense [38] irrespective of physical (mycelial) connections among fungi.…”

“…The 3,862,747 reads that passed the filtering processes were clustered with a cutoff sequence similarity of 97% in a parallelized process of the Minimus for accurate assembling/clustering [54] as implemented in Claident and the obtained consensus sequences were then used as operational taxonomic units (OTUs) in the following statistical analyses. In the clustering process, reads of each sample were clustered beforehand with a 98% cutoff similarity: the results of the within-sample dereplication was used as guide information in order only to accelerate the 97% clustering process [35, 43]. OTUs whose sequencing reads were less than ten in all the samples were removed because their sequences could contain PCR/sequencing errors [55].…”

“…Therefore, molecular taxonomic identification of OTUs was performed based on the database search algorithm of the query-centric auto- k -nearest-neighbor (QCauto) method [50] and subsequent taxonomic assignment with the lowest common ancestor (LCA) algorithm [59] using Claident [35, 43]. A benchmark analysis has shown that the QCauto-LCA pipeline allows the most accurate identification among the existing algorithms of automated taxonomic identification [50].…”

“…A benchmark analysis has shown that the QCauto-LCA pipeline allows the most accurate identification among the existing algorithms of automated taxonomic identification [50]. We applied the QCauto algorithm to the obtained OTUs using the databases provided by filtering out unreliable sequence entries from the NCBI “nt” database (downloaded from ftp://ftp.ncbi.nlm.nih.gov/ on January 27, 2015) [35, 43, 50]. The taxonomic identification results of both QCauto-LCA and UCLUST-UNITE approaches are shown in S1 Data.…”

Communities of Putative Ericoid Mycorrhizal Fungi Isolated from Alpine Dwarf Shrubs in Japan: Effects of Host Identity and Microhabitat

“…Ishida and Nordin (29) identified such host effects on ERM fungal communities in V. vitis-idaea and V. myrtillus in northern Sweden. Toju et al (56) reported significant host preferences in root-associated fungi in 3 out of 16 ericaceous plant species on Mt. Tateyama, Japan.…”