Note: Because SERC science seminars are directed towards a scientific audience, they are more technical than our monthly evening lectures.

Summary:
As the second-strongest greenhouse gas in the atmosphere, methane (CH₄) plays a critical role in our ability to mitigate global warming.  However, global inventories of CH₄ sources and sinks are not adequately constrained to provide efficient options to decrease atmospheric CH₄. It has proven difficult to accurately predict CH₄ fluxes from terrestrial ecosystems with only the existing knowledge of net ecosystem fluxes (e.g., soil surface flux), pointing to a need for understanding the hidden, gross CH₄ fluxes (e.g., belowground) that compose net fluxes. In this seminar, SERC postdoc Paul Brewer will talk about research on methane fluxes in agricultural soils like those in the North American Great Plans, as well as research into how trees in upland forests are emitting methane.  In the agricultural study, bare soils had short-term CH₄ production controlled by available organic matter and long-term production controlled by soil moisture. However CH₄ production in vegetated soils was strongly affected by an undetermined source, possibly rhizosphere microsites or macrofaunal guts.  These results reveal there are complex mechanisms underlying the well-established decrease in net CH₄ sink capacity of tilled soils and that other management choices.

Healthy upland trees are a newly discovered CH₄ source, but little is known regarding the biological source, physical flowpaths, plant physiological effects, and environmental controls of this unexpected flux.  An automated gas sampling array has been developed and deployed for ongoing hourly quantification of CH₄ and CO₂ fluxes made alongside measurements of environmental properties and molecular analyses. This approach will provide a detailed, novel dataset that should allow the characterization of the size and governing factors of temperate tree gas fluxes.