Geographical Isolation and Root-Associated Fungi in the Marine Terrains: A Step Toward Establishing a Strategy for Acquiring Unique Microbial Resources

Abstract

This study aimed to understand whether the geo-ecological segregation of native plant species affects the root-associated fungal community. Rhizoplane (RP) and rhizosphere (RS) fungal microbiota of Sedum takesimense native to three geographically segregated coastal regions (volcanic ocean islands) were analyzed using culture-independent methods: 568,507 quality sequences, 1399 operational taxonomic units, five phyla, and 181 genera were obtained. Across all regions, significant differences in the phyla distribution and ratio were confirmed. The Chao's richness value was greater for RS than for RP, and this variance coincided with the number of genera. In contrast, the dominance of specific genera in the RS (Simpson value) was lower than the RP at all sites. The taxonomic identity of most fungal species (95%) closely interacting with the common host plant was different. Meanwhile, a considerable number of RP only residing fungal genera were thought to have close interdependency on their host halophyte. Among these, Metarhizium was the sole genus common to all sites. These suggest that the relationship between potential symbiotic fungi and their host halophyte species evolved with a regional dependency, in the same halophyte species, and of the same natural habitat (volcanic islands); further, the fungal community differenced in distinct geographical regions. Importantly, geographical segregation should be accounted for in national culture collections, based on taxonomical uniqueness.

Keywords: Fungal community; Metarhizium; geographical segregation; rhizoplane; rhizosphere.

Figure 1.

Geographical location and segregation of each sampling site. (A) Geographical location of the Ulleungdo and Dokdo Islands. The two volcanic islands are ecologically segregated from mainland and each other. (B) Site 1: Dongdo island of the Dokdo Islands. (C) Ulleungdo Islands; (C1) Site 2: Sadong, slope cliff near the seashore, (C2) Site 3: Primitive virgin forest in Taeha in the Ulleungdo Islands. The sampling sites are circled. The map images were downloaded from the Cultural Heritage Administration of Korea (CHA) Portal Site (http://www.heritage.go.kr/heri/idx/index.do., accessed on 21 October 2020) and modified for this study.

Figure 2.

Rarefaction curves for operational taxonomic units (OTUs) from each site. OTUs were clustered at 3% dissimilarity using CD-HIT. The microbial community in the rhizoplane and the rhizosphere of Dongdo, Dokdo Islands (OTUs, 140/341; sequencing reads, 84,267/94,745), Sadong, Ulleungdo Islands (OTUs, 154/389; sequencing reads, 95,395/117,939), and Taeha (OTUs, 212/478; sequencing reads, 86,299/89,864) are shown.

Figure 3.

Fungal diversity variation from rhizoplane to rhizosphere in each island. The Simpson’s Diversity Index quantifies the biodiversity of a habitat, and considers the number of species present, and the abundance of each species. The Shannon’s diversity index (H) accounts for both abundance and evenness of the species.

Figure 4.

Chao fungal genera richness index variation from rhizoplane to rhizosphere in each island. The Chao1 index is used to estimate the richness (estimated richness; measurement of OTUs expected in samples given all the bacterial species identified in the samples).

Figure 5.

Comparison of the variation in dominant fungal phyla between the rhizosphere and the rhizoplane. Differences are highlighted. The dominance ratio (%) is represented per fungal phyla. Comparing the sites, the rank, and ratio of dominance are similar in the rhizoplane of all sampling sites, but with the rhizosphere areas, more affected by the marine environment, a change in the order of dominance was observed for each sampling point.

Figure 6.

Unique fungal genera distribution in each coastal region. Fungal microbiota structures were different in each of the coastal regions. Only those fungal genera that accounted for 0.7% or more of each community were labeled. The ratio (%, dominance) of each fungal genus.