Meta-analysis of net microbial methane oxidation by non-wetland soils

Methane (CH₄) is one of the most potent anthropogenic greenhouse gases, second in climate change impact only to CO₂. Since 1850, the atmospheric methane concentration has more than doubled. In recent decades, the increase in the atmospheric concentration of methane has significantly slowed at a time when known sources of methane are increasing. The primary natural and anthropogenic source of methane is methanogenic microorganisms, which occur in anaerobic soil zones and some freshwater systems. The primary natural destruction of methane occurs in the atmosphere, with the secondary sink being consumption by methanotrophic microorganisms that occur in aerobic zones of soil. The balance of methanogenesis and methanotrophy results in ecosystem-level net methane emission or uptake, estimates of which are used in global climate models. Terrestrial, non-wetland systems often exhibit methane uptake, however studies in natural systems are lacking. A meta-analysis of the primary literature by ecosystem type on net uptake yields extremely high variability in estimates, but our bottom-up, globally averaged estimate of methane uptake is approximately twice that currently being used in climate models. This finding suggests that predictions of climatic change may be based on invalid assumptions about the methane cycle. Key environmental parameters that affect the variability in consumption strength, such as soil type, soil water holding capacity and position on slope, are identified across studies. Recommendations are made identifying the types of ecosystems and environmental parameters that should be more intensively studied to elucidate the uncertainties in the modern methane cycle.