Vegetation regulation of warming impacts on belowground C cycling and methane emission in a temperate peatland

Abstract:

Peatlands are one of the largest natural sources of atmospheric methane (CH₄), a potent greenhouse gas; therefore, understanding the impacts of changing environments on peatland CH₄ emissions are critically important for understanding the implications for climate forcing. Climate warming has been found to stimulate peatland CH₄ emissions; however, the underlying mechanisms for this stimulating impact remain understudied. A newly developed terrestrial biosphere model – ELM_SPRUCE – was integrated with observational data obtained from the SPRUCE (Spruce and Peatland Responses Under Changing Environments) project; the model was then applied to understand the CH₄ processes in a northern temperate peatland under a gradient of warming treatments. Warming accelerates all belowground C cycling processes, including mineralization of soil organic matter (SOM) and dissolved organic carbon (DOC), and acetate production and consumption. Warming also enhances acetoclastic and hydrogenotrophic methanogenesis, and surface CH₄ emissions that lead to slightly lower CH₄ concentrations in soil profiles. Further modeling analysis indicates that warming-induced increases in vegetation evapotranspiration (in agreement with observations) can reduce the water table depth, increasing methane oxidation in the upper acrotelm and thereby buffering CH₄ emissions. The magnitude of warming effects diminishes over time, indicating strengthening hydrological feedback and substrate depletion. An isotopic modeling capability confirms the accelerated belowground C cycling and its contribution to increased CH₄ emission. The scenario analysis shows that the hydrological feedbacks were strong in the first few years and then diminished after four years of warming. The vegetation regulation of the warming impacts on CH₄ cycling under warming confirm the complexity of belowground hydrological and biogeochemical processes that calls for more mechanistic experimental investigations and modeling studies to better understand the magnitude of hydrological feedbacks on peatland CH₄ flux.