Pairing Field Measurements with Stable Isotope Pool Dilution Shows Acclimation of Gross and Net Methane Fluxes from 4-Year-Old Transplanted Soil Monoliths


Kendalynn Morris1* (, Anya Hoople2, Stephanie Pennington1, Patrick Megonigal2, Stephanie Yarwood4, Mitchell Smith5, Roberta Peixoto6, Donnie Day6, Nora Hamovit4, Jaehyun Lee7, Kaizad Patel3, Nicholas Ward8, Stephanie Wilson2, Ben Bond-Lamberty1, Vanessa Bailey3


1Joint Global Change Research Institute, College Park, MD; 2Smithsonian Environmental Research Center, Edgewater, MD; 3Pacific Northwest National Laboratory, Richland, WA; 4University of Maryland–College Park, MD; 5Ohio University–Athens, OH; 6University of Toledo, Toledo, OH; 7Yonsei University, Seoul, South Korea; 8Marine and Coastal Research Laboratory, Sequim, WA



Rising waters in response to global change are shifting coastal terrestrial-aquatic interfaces (TAIs) into previously upland, freshwater-dominated ecosystems. This may result in coastal forest soils transitioning from an atmospheric methane (CH4) sink to a source, but the sources, timing, and magnitude of such shifts are poorly understood. To disentangle the role of biotic and abiotic factors in soil CH4 fluxes at coastal TAIs, researchers transplanted soil monoliths from upland to wetland-edge locations (and vice versa) and measured their characteristics and greenhouse gas fluxes over four years. To delve deeper into the microbial processes driving net fluxes measured at the soil surface, researchers used a 13CH4 pool dilution technique to quantify gross methanogenesis and methanotrophy in both transplanted and local soils. The team found that field-net and laboratory-gross rates in transplanted soils were similar in magnitude, regardless of soil origin. The acclimation-to-local conditions indicate low resistivity of CH4 flux to changes in abiotic conditions. However, gross fluxes from surface soils poorly tracked net fluxes from the integrated soil column. The results demonstrate that soil CH4 production may rapidly increase in response to increased inundation with estuarine water, and that this flux is more responsive across column depth than increases in CH4 consumption. Future work will focus on (1) measuring gross rates across depth; (2) determining the relative importance of key features of TAIs, saturation and redox sensitive chemical species; (3) attributing methanogenic (e.g., acetoclastic, hydro-genotrophic) and methanotrophic (oxidation vs anaerobic) processes to measured gross fluxes and their respective taxonomic members; and (4) quantifying how these relationships vary across the broader range of TAI sites that are part of the Coastal Observations, Mechanisms, and Predictions Across Systems and Scales–Field, Measurements, and Experiments project.