Agriculture’s impact on microbial diversity and associated fluxes of carbon dioxide and methane

Agriculture has marked impacts on the production of carbon dioxide (CO2) and consumption of methane (CH4) by microbial communities in upland soils—Earth's largest biological sink for atmospheric CH4. To determine whether the diversity of microbes that catalyze the flux of these greenhouse gases is related to the magnitude and stability of these ecosystem-level processes, we conducted molecular surveys of CH4-oxidizing bacteria (methanotrophs) and total bacterial diversity across a range of land uses and measured the in situ flux of CH4 and CO2 at a site in the upper United States Midwest. Conversion of native lands to row-crop agriculture led to a sevenfold reduction in CH4 consumption and a proportionate decrease in methanotroph diversity. Sites with the greatest stability in CH4 consumption harbored the most methanotroph diversity. In fields abandoned from agriculture, the rate of CH4 consumption increased with time along with the diversity of methanotrophs. Conversely, estimates of total bacterial diversity in soil were not related to the rate or stability of CO2 emission. These combined results are consistent with the expectation that microbial diversity is a better predictor of the magnitude and stability of processes catalyzed by organisms with highly specialized metabolisms, like CH4 oxidation, as compared with processes driven by widely distributed metabolic processes, like CO2 production in heterotrophs. The data also suggest that managing lands to conserve or restore methanotroph diversity could mitigate the atmospheric concentrations of this potent greenhouse gas.