Chemolithotrophic microbiome of buried soil layers following volcanic eruptions: A potential huge carbon sink

Abstract

Soil burial processes create large pools of soil organic carbon that have been sequestered in the deep for long periods of time. This buried organic carbon is generally thought to be stable and resistant to decomposition, consisting of the remains of past plants and soil microbes. As a result, there is a lack of research on the role of microbiomes in the carbon transformation processes that may occur in the deep buried soil layers. In this study, we characterized the microbiomes and their metabolic potentials in organic soil layers buried following the volcanic eruption approximately 300 and 1,640 years ago, using bacterial and archaeal 16S rRNA gene sequencing. Both buried layers had comparable or even larger carbon and nitrogen contents and a microbial population as abundant and diverse as that of the surface layer. However, the organic soil layer buried 1,640 years ago showed a distinct microbiome from the surface layer, with a higher proportion of chemolithotrophic taxa, such as methanogens and NH3-oxidizing archaea. Additionally, this buried layer had a higher metabolic potential for fixing CO2 and synthesizing organic matter, while the surface community had a higher potential for degrading organic matter. These findings suggest that the buried organic soil in the deep may not simply be an accumulation of past organisms, but rather an active carbon sink driven by a chemolithotrophic microbiome that differs from the organotrophic microbiome of the surface soil.