Soil Inorganic Electron Acceptors and Carbon Substrates Hierarchically Govern Wetland Methanogenesis Temperature Response.

Wetlands constitute Earth's largest natural methane (CH4) source, yet projections of their climate feedback remain uncertain due to poorly constrained temperature sensitivity (Q10-CH4) of microbial methanogenesis. While water table dynamics have been demonstrated to regulate wetland methanogenesis by altering key soil conditions such as inorganic terminal electron acceptors (TEAs) and carbon substrates, the influence of these biogeochemical factors on Q10-CH4 remains unclear, particularly at continental scales. Here, we assess Q10-CH4 across 69 wetlands (276 soil samples) spanning diverse climatic and hydrological regimes. We find that Q10-CH4 varies substantially (1.12-7.75) independent of climatic factors, instead being hierarchically controlled by soil TEAs and carbon-to-nitrogen (C/N) ratio. Soil TEAs serve as the overarching determinant that dampens Q10-CH4 at a large scale through thermodynamic constraints. Notably, the promoting effect of C substrate quality (C/N ratio) on temperature sensitivity is conditional, emerging as a dominant driver only when soil TEA concentrations are sufficiently low to alleviate thermodynamic suppression. Our findings suggest that the intrinsic biogeochemical state of wetland soils dictates the magnitude of microbial-driven CH4 emission responses to warming, with critical implications for predicting wetland CH4-climate feedbacks.