Kinetic and environmental controls on the soil methane sink and its sensitivity to global change

Aerobic methanotrophy is the only Earth surface sink for atmospheric methane, and today it accounts for ~5% of the total methane sink. However, this sink size is certain to change in response to future changes in atmospheric methane levels, climate, and land use. We have undertaken computational and field-based work to investigate the sensitivity of the soil methane sink to these global changes. To predict the response of the soil methane sink to changing atmospheric methane, we generated a comprehensive compilation of methanotrophy kinetic data. Trends in kinetic data demonstrate the potential for rising atmospheric methane to strongly enhance soil methanotrophy. The methanotrophy kinetic parameters in our compilation are highly variable—both the Vmax (oxidation rate at saturation) and KM (half-saturation constant) in natural samples span over six orders of magnitude. However, accounting for a correlation we observe between Vmax and KM reduces the range of projected uptake rates by as much as 96%. Additionally, our results indicate that variation in enzyme kinetics introduces a similar magnitude of variation in the calculated soil methane sink as temperature sensitivity. These findings emphasize the importance of enzyme kinetics in soil methane sink projections. To assess the sensitivity of the soil methane sink to climate and land use, we collected two years of seasonal data at three locations spanning diverse arid-semiarid ecoregions and land use types. Contrary to our expectations, the spatial variability in methane consumption across individual landscapes is similar in amplitude to the variability among landscapes with very different climate and land use. In contrast to parameterizations in many models, we did not observe significant correlations between methane consumption and soil or air temperatures. Methane fluxes correlated most strongly with microbial community structure. This work highlights the importance of soil ecology to modern and future soil methane uptake in an arid landscape.