Date:
Location:
Xinning Zhang
Assistant Professor
Princeton University, Dept of Geosciences
The wetland methane paradox: how does O2enhance methane production?
Methane (CH4), a potent greenhouse gas produced primarily in nature by oxygen (O2)-sensitive methanogenic Archaea, is the second most important greenhouse gas contributor to climate change. Wetlands constitute large and highly variable natural methane sources and are predicted to play an important role in future carbon-climate feedbacks. A mechanistic understanding of the complex and dynamic interplay between microbial, hydrological, and plant-associated processes in wetlands is critical to deciphering current atmospheric trends in methane and predicting future emissions.Recent studies suggest alarge fraction of wetland methane can originate from anoxic microsites within oxygenated regions of soils and peats. I will discuss research aimed at resolving how O2, an inhibitor of methanogenesis, can stimulate wetland methane production. We focus on the role of oxic-anoxic transitions as a control on biogeochemical transformation to methane. Using bottle incubations of Sphagnum peat, we find that prior oxygen exposure during a temporal redox oscillation from oxic to anoxic conditions dramatically enhances methane yields by ~20-2000 fold compared to peat incubated under continuous anoxia. Analyses of the chemistry and microbial community in peats indicate that O2initiates a biogeochemical cascade in which aerobic microbes efficiently degrade and mineralize complex peat carbon. The breakdown of polyphenolic peat constituents by aromatic oxygenases provides CO2and H2precursors for hydrogenotrophic methanogenesis during the subsequent anoxic period. The results imply a critical role for oxic-anoxic transitions in modulating wetland CH4production, highlighting the need to consider hydrologically-associated spatial and temporal oxygen gradients across multiple scales in experimental and modeling studies of wetland methane. Results also have implications for management of wetlands to mitigate greenhouse gas emissions.
