Date Published: October 12, 2018
Publisher: Public Library of Science
Author(s): Jong-Shik Kim, Dae-Shin Kim, Keun Chul Lee, Jung-Sook Lee, Gary M. King, Sanghoon Kang, Lorenzo Brusetti.
The Gotjawal areas of Jeju Island, Korea, are comprised of unmanaged forests growing on volcanic soils. They support unique assemblages of vascular plants from both northern and southern hemispheres, but are threatened by human disturbance. The health and ecosystem function of these assemblages likely depends in part on the diversity and community structure of soil microbial communities, about which little is known. To assess the diversity of Gotjawal soil microbial communities, twenty samples were collected in November 2010 from 4 representatives of Gotjawal forests. While soil properties and microbial communities measured by 16S rRNA gene sequence data were marginally distinct among sites by PERMANOVA (p = 0.017–0.191), GeoChip data showed significant differences among sites (p <0.006). Gene composition overall, and the composition of 3 functional gene categories had similar structures themselves and similar associations with environmental factors. Among these communities, phosphorous cycling genes exhibited the most distinct patterns. 16S rRNA gene sequence data resulted in a mean 777 operational taxonomic units (OTUs), which included the following major phyla: Proteobacteria (27.9%), Actinobacteria (17.7%), Verrucomicrobia (14.3%), Acidobacteria (9.6%), Planctomycetes (9.8%), Bacteroidetes (8.9%), and Chloroflexi (2.2%). Indicator species analysis (ISA) was used to determine the taxa with high indicator value, which represented the following: uncultured Chlamydiaceae, Caulobacter, uncultured Sinobacteraceae, Paenibacillus, Arenimonas, Clostridium sensu.stricto, uncultured Burkholderiales incertae sedis, and Nocardioides in Aewol (AW), Aquicella, uncultured Planctomycetia, and Aciditerrimonas in Gujwa-Seongsan (GS), uncultured Acidobacteria Gp1, and Hamadaea in Hankyeong-Andeok (HA), and Bosea, Haliea, and Telmatocola in Jocheon-Hamdeok (JH) Gotjawal. Collectively, these results demonstrated the uniqueness of microbial communities within each Gotjawal region, likely reflecting different patterns of soil, plant assemblages and microclimates.
On Jeju Island, Korea, the term “Gotjawal” refers to a unique natural unmanaged forest that grows on widely distributed lava-based formations characterized by dense stands of trees and shrub undergrowth. The Gotjawal provides numerous ecosystems services, including groundwater purification, that have supported human occupation historically. At present, some areas of the Gotjawal are protected, but about 50% of the original forests have been replaced by secondary growth due to losses from deforestation, agricultural land use, and urbanization. Gotjawal soils are considered highly fertile due to their high organic matter and low mineral content, but relatively little is known about their microbiology[2, 4]. Previous cultivation-based studies of these soils have identified several new genera and species [2, 4–8], but more comprehensive analyses are needed to understand patterns of microbial community structure and function, and interactions with Gotjawal plant assemblages.
Microbial community structure and functional potential in the Gotjawal soils was investigated using 16S rRNA gene sequencing and GeoChip hybridization. The results demonstrated that each of four Gotjawal regions contained distinctly different soil microbial communities as defined by 16S rRNA genes and nutrient cycle functional genes (Table 2). The microbial communities based on functional gene category were similar in structure, and had similar associations with environmental factors. However, P cycling genes were the most distinctive gene category, possibly due to the different geological features and vegetation of the Gotjawal areas (S2 Table). However, further careful analysis is required to support this result.