Date: 17th May 2019
Title: Methane Production and Emissions in Trees and Forests
Location: Seminar room 1015, Biocentre 2, Viikinkaari 5
Host: Mari Pihlatie
Abstract: Forests are dominant terrestrial sources and sinks of greenhouse gases (GHG) and have been a focus of carbon cycling research for decades. Most GHG research in forests emphasizes fluxes across leaf or soil surfaces, with little attention to fluxes across tree stems. Furthermore, forest GHG studies rarely quantity CH4 fluxes even though it has a century-scale impact on radiative forcing that is 45-times greater than CO2. In the past decade, a global community of ecologists, foresters, ecophysiologists, and soil scientists have been investigating trees as CH4 sources and CH4 sinks. Trees are now recognized as potentially large and unconstrained CH4 sources. Tree stems in the Amazon floodplain alone account for 3% of global CH4 emissions, and upland forest tree stems emit enough CH4 to offset up to 60% of the CH4 consumed by upland soils. All parts of a forest are capable of contributing to CH4 sources and sinks. Living and dead trees transport and emit CH4 that was produced in soils; living trees and deadwood emit CH4 produced inside trees by microorganisms; and trees produce CH4 through an abiotic photochemical process. I will review the state of the science on the production, consumption, transport, and emission of CH4 by living and dead trees, and the spatial and temporal dynamics of these processes across hydrologic gradients inclusive of wetland and upland ecosystems. Scaling from stem or leaf measurements to trees or forests is limited by our knowledge of the mechanisms by which trees transport soil-produced or tree-produced CH4, the microbial processes that produce and oxidize CH4 inside trees, and complex interactions between soil and tree biophysical processes. Understanding the complex CH4 source-sink dynamics in trees and forests requires cross-disciplinary research and new conceptual models that transcend the traditional binary classification of wetland versus upland forest.
Patrick Megonigal is an ecosystem ecologist and biogeochemist with research interests in plant-microbe interactions that regulate carbon cycling and greenhouse gas emissions in wetlands and forests, particularly as they relate to global change. He is the lead investigator of the Global Change Research Wetland, a facility dedicated to long-term experiments on coastal wetland responses to elevated carbon dioxide, warming, eutrophication, and invasive plant species. His group studies plant-microbe-soil interactions that confer stability on coastal marshes as they respond to accelerated sea level rise, and they develop both local-scale and earth-scale numerical models of these processes. Patrick is especially interested in the microbial processes that regulate methane production, oxidation, and emissions from trees, forests, and wetlands.