Environmental Transformations and Interactions
The Surprising Role of Plant-Mediated Oxygen Transport in Coastal Wetlands
New study challenges conventional thinking that warming temperatures and elevated carbon dioxide lead to increased methane emissions.
Long-term experiments at the Smithsonian’s Global Change Research wetland, a tidal marsh along the Chesapeake Bay, are teaching scientists how interactions among plants, microbes, and oxygen flux can affect levels of carbon and methane in the environment. (Image courtesy of University of North Carolina Wilmington Coastal and Estuarine Studies Lab)
The Science
Many models of global climate change assume that warming temperatures and higher levels of carbon dioxide are tightly linked, but scientists have found it challenging to study these two factors in field experiments. In a four-year study in a tidal marsh on the Chesapeake Bay, scientists manipulated conditions and observed changes more closely than ever before. Their surprising results showed that warmer temperatures and higher levels of carbon dioxide could actually result in less carbon in the soil and less methane released to the atmosphere, and that these outcomes were dependent on the complex interactions among plants, microbes, and oxygen fluxes in tidal marsh soils.
The Impact
The interdependence of plants, microbes, and their environment means that ecosystem responses to climate change can only be thoroughly understood through field experiments that include both above- and belowground components. This ambitious field study upended commonly held beliefs about the link between warming temperatures and increased carbon dioxide in a tidal marsh. Scientists had expected the plants in the marsh to fix carbon in the inundated soil at a greater rate and microbes to release more methane as temperature and carbon dioxide were increased. Instead, through a process called oxygen priming, less carbon and methane were captured and released. Understanding this plant–microbe feedback loop will help scientists better predict the effects of climate change on tidal marshes.
Summary
Over the course of four years, a multi-institutional team of scientists manipulated temperature and carbon dioxide (CO₂ levels in a coastal wetland to understand their effect on methane emissions. They monitored changes in such factors as stem density and root productivity in bulrush plants, soil carbon sequestration, and methane emissions. They also analyzed the dissolved organic carbon in soil porewater using the 21T Fourier-transform ion cyclotron resonance advanced instrument at EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science user facility. Initial results from their work indicated that these plants were transporting oxygen through the inundated soil, which drove changes in microbial respiration and overall ecosystem functioning. To test this, they developed an automated approach that tracked changes in the oxidation state of the soil every 30 minutes. These high-frequency measurements yielded a wealth of data that pointed to the important role of plant-mediated oxygen transport in an ecosystem’s response to elevated temperature and CO₂. The findings challenge current thinking on the link between global warming and carbon storage by tidal wetlands.
Contacts
Pat Megonigal, Smithsonian Environmental Research Center and EMSL (joint appointment), megonigalp@si.edu
Genevieve Noyce, Smithsonian Environmental Research Center, noyceg@si.edu
Funding
Funding for this project was provided by the DOE Office of Science, Biological and Environmental Research program; the National Science Foundation; and the Smithsonian Institution. A portion of the research was performed at EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility.
Publications
G.L. Noyce, et al., “Oxygen priming induced by elevated CO₂ reduces carbon accumulation and methane emissions in coastal wetlands.” Nature Geoscience 16, 63 (2023). [DOI: 10.1038/s41561-022-01070-6]