Mofettes as Models for Basic Research on Soil and Rhizosphere Microbial Communities and Possible Applications of These Extreme Ecosystems

Mofettes or natural CO2 springs release large amounts of geogenic CO2 at ambient temperature, leading to long-term soil hypoxia in these extreme ecosystems. Thus, they can serve as natural long-term experiments in ecology and evolution and other environmental studies, providing stable long-term changes in abiotic factors that are most pronounced in mofette soils. This paper reviews basic research on rhizosphere processes, soil microbial communities, and microbial diversity in mofettes, focusing on reports describing the effects of altered soil gas regimes on root respiration and the diversity and community structure of archaea, bacteria, and fungi in soil. Furthermore, an insight into possible applications of mofette ecosystems is given. For more than 20 years, mofettes have provided new insights into the importance of long-term changes in abiotic environmental factors in regulating soil biodiversity, serving as a model for extreme ecosystems. Mofettes provide an innovative approach to the study of many ecological processes that occur slowly and, therefore, require extensive and lengthy observations and experiments, acting as a space-for-time substitution. Previous studies in mofettes around the world have determined plant responses to elevated CO2 concentrations over multiple generations, described new species of collembolans and yeasts, and identified stable patterns in microbial communities describing specific acidophilic and methanogenic consortia of soil archaea and bacteria, as well as stable communities of plant symbiotic arbuscular mycorrhizal fungi. As the development of high-throughput molecular techniques has accelerated rapidly in the last decade, mofettes now serve more than ever as a natural long-term experimental system to study soil and rhizosphere ecology and contribute to further research on long-term ecological and evolutionary processes that are crucial for understanding past evolutionary events, managing future ecosystems, and predicting ecological responses to global change. Some recent developments target the specific geological and biological characteristics of these extreme ecosystems, including in terms of applications related to environmental impact assessment of carbon capture and storage systems, as well as conservation status, tourism, culture and education, i.e., broader ecosystem services of mofettes, which are addressed in this review together with basic research on soil biodiversity.