Impacts of naturally elevated soil CO₂ concentrations on communities of soil archaea and bacteria

Nataša Šibanc, Alex J. Dumbrell, Ines Mandic-Mulec, Irena Macek

Biotechnical Faculty, Department of Agronomy, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.

Abstract

There is a limited understanding of the importance of abiotic factors in regulating biodiversity and structure of many functionally important soil microbial communities. In this paper we present a molecular characterisation of archaeal and bacterial communities, exposed to long-term change in soil abiotic environment at natural CO₂ springs (mofettes), using T-RFLP profiling and examination of 16S rRNA clone libraries. Our results show major shifts in archaeal and bacterial communities towards anaerobic and methanogenic taxa dominating in CO₂ rich hypoxic soils with a significant increase in abundance of Methanomicrobia and predominantly anaerobic Chloroflexi and Firmicutes. O₂ concentration in soil was consistently shown to be the strongest predictor of the compositional changes across both the archaeal and bacterial communities. However, soil pH and total N, were most important in separating the archaeal communities in transition and control zones, but not the bacterial communities. We conclude that geological CO₂ induced hypoxia in mofette systems can cause major shifts in community composition of soil microbes that can generate significant implications for ecosystem functioning (e.g. nutrient cycling and CH₄ production). Our data indicate that mofettes offer a good model system for studying the response of natural microbial communities to long-term environmental changes, which is urgently needed to address the bias towards macro-organisms in soil biodiversity research.

Keywords: Soil biodiversity; Aboveground–belowground interactions; Terminal restriction fragment length polymorphisms; 16S rRNA; Extreme environment; Hypoxia; Mofettes; Natural CO₂ springs; Carbon capture and storage (CCS).