A microbial functional group-based module for simulating methane production and consumption: Application to an incubated permafrost soil

Accurately estimating methane (CH₄) flux in terrestrial ecosystems is critically important for investigating and predicting biogeochemistry-climate feedbacks. Improved simulations of CH₄ flux require explicit representations of the microbial processes that account for CH₄ dynamics. A microbial functional group-based module was developed, building on the decomposition subroutine of the Community Land Model 4.5. This module considers four key mechanisms for CH₄ production and consumption: methanogenesis from acetate or from single-carbon compounds and CH₄ oxidation using molecular oxygen or other inorganic electron acceptors. Four microbial functional groups perform these processes: acetoclastic methanogens, hydrogenotrophic methanogens, aerobic methanotrophs, and anaerobic methanotrophs. This module was used to simulate dynamics of carbon dioxide (CO₂) and CH₄ concentrations from an incubation experiment with permafrost soils. The results show that the model captures the dynamics of CO₂ and CH₄ concentrations in microcosms with top soils, mineral layer soils, and permafrost soils under natural and saturated moisture conditions and three temperature conditions of -2°C, 3°C, and 5°C (R²>0.67; P<0.001). The biases for modeled results are less than 30% across the soil samples and moisture and temperature conditions. Sensitivity analysis confirmed the importance of acetic acid's direct contribution as substrate and indirect effects through pH feedback on CO₂ and CH₄ production and consumption. This study suggests that representing the microbial mechanisms is critical for modeling CH₄ production and consumption; it is urgent to incorporate microbial mechanisms into Earth system models for better predicting trace gas dynamics and the behavior of the climate system.