Methanogenesis
When oxygen is absent (i.e. in waterlogged conditions), decomposition of organic molecules results in the production of methane (CH4) rather than carbon dioxide (CO2). This process is performed by a group of microorganisms (methanogens) that belong to Archaea. It is estimated that about 70% of the CH4 in the atmosphere is produced by methanogens. Soils significantly contribute to this. When conditions are wet, CH4 is formed in the waterlogged layers of the soil and travels up the soil profile into the atmosphere.
Methanogenesis is the final step in anaerobic (oxygen poor) decomposition and thus supports the Carbon and Climate Regulation function. As a greenhouse gas, CH4 is 25 times more powerful than CO2. The amount of CH4 a soil releases is held in check by the opposing process of methanotrophy (methane consumption).
The production of CH4 can be measured under lab and field conditions by measuring the change in CH4 concentration in a closed space, over a period of time[1],[2],[3]. Alternatively, the genes that the methanogenic archaea use to perform the process can be measured with DNA-based techniques[1],[2].
[1] Freitag, T. E. & Prosser, J. I. 2009. Correlation of Methane Production and Functional Gene Transcriptional Activity in a Peat Soil. Applied and Environmental Microbiology 75, 6679–6687.
[2] Qi, L. et al. 2021. Biochar decreases methanogenic archaea abundance and methane emissions in a flooded paddy soil. Science of the Total Environment 752, 141958.
[3] Oram, N. J. et al. 2020. Can flooding-induced greenhouse gas emissions be mitigated by trait-based plant species choice? Science of the Total Environment 727, 138476.