Metagenomic analysis reveals rapid development of soil biota on fresh volcanic ash

Hokyung Song,Jonathan Adams,Sophie L Nixon,Dorsaf Kerfahi,Hyoki Kim,Koichi Takahashi,Binu M Tripathi,Ryunosuke Tateno

doi:10.1038/s41598-020-78413-z

Abstract

Little is known of the earliest stages of soil biota development of volcanic ash, and how rapidly it can proceed. We investigated the potential for soil biota development during the first 3 years, using outdoor mesocosms of sterile, freshly fallen volcanic ash from the Sakurajima volcano, Japan. Mesocosms were positioned in a range of climates across Japan and compared over 3 years, against the developed soils of surrounding natural ecosystems. DNA was extracted from mesocosms and community composition assessed using 16S rRNA gene sequences. Metagenome sequences were obtained using shotgun metagenome sequencing. While at 12 months there was insufficient DNA for sequencing, by 24 months and 36 months, the ash-soil metagenomes already showed a similar diversity of functional genes to the developed soils, with a similar range of functions. In a surprising contrast with our hypotheses, we found that the developing ash-soil community already showed a similar gene function diversity, phylum diversity and overall relative abundances of kingdoms of life when compared to developed forest soils. The ash mesocosms also did not show any increased relative abundance of genes associated with autotrophy (rbc, coxL), nor increased relative abundance of genes that are associated with acquisition of nutrients from abiotic sources (nifH). Although gene identities and taxonomic affinities in the developing ash-soils are to some extent distinct from the natural vegetation soils, it is surprising that so many of the key components of a soil community develop already by the 24-month stage. In this system, however, rapid development may be facilitated by the relatively moderate pH of the Sakurajima ash, proximity of our mesocosms to propagule sources, and the rapid establishment of a productive bryophyte and lichen layer on the surface. Ash from other volcanoes richer in acids or more distant from propagule sources could show a different pattern and slower soil biota development.

Highlights

Little is known of the earliest stages of soil biota development of volcanic ash, and how rapidly it can proceed
Total carbon and total nitrogen concentrations were significantly lower in the ash soils, irrespective of location and age. pH was significantly lower in the ash soils in Sakurajima and Takakuma, but no such pattern was found in other sites
Bacterial community composition and diversity analysed based on the 16S rRNA gene amplicon sequencing

Summary

Introduction

Little is known of the earliest stages of soil biota development of volcanic ash, and how rapidly it can proceed. A metagenome study by Fujimura et al.[3] compared the functional gene profile of 3.5-, 6.6-, and 9.5-year old ash from the Miyakejima volcano in Japan and noted that the rbcL gene for C O2 fixation and nifH gene for nitrogen fixation were more abundant in the developing ash-soils. These genes have been suggested to be important for energy, carbon and Scientific Reports | (2020) 10:21419. Our intention was to understand how rapidly a soil biota appears in the ash, how it may differ from more developed soils, and whether climate and location have a large effect on the development of biota

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Discussion

Conclusion