Trait-Based Modeling of Peatland Methanogen Communities

Methanogens are methane-producing archaea that play a major role in the global carbon cycle. However, despite their importance, the community dynamics of these organisms have not been thoroughly characterized or modeled. In the majority of methanogenesis models, the communities are approximated as a chemical reaction or divided into two populations based on the most common methanogenic pathways. These models provide reasonable estimate of methanogenesis rates but cannot predict community structure. In this work, a trait-based model for methanogenic communities in peatlands is developed. The model divides methanogens commonly found in wetlands into ten guilds, with divisions based on factors such as substrate affinity, pH tolerance, and phylogeny. The model uses steady-state, mixotrophic Monod kinetics to model growth and assumes peatlands operate as a semi-batch system. An extensive literature review was performed to parameterize the model. The acetoclastic module of the model was validated against experimental data. It was found that this portion of the model was able to reproduce the major result of an experiment that examined competition between Methanosaeta and Methanosarcina species under irregular feeding conditions. The model was analyzed as a whole using Monte Carlo simulation methods. It was found that equilibrium membership is negatively correlated with a guild's half-substrate constant, but independent of the guild's yield. These results match what is seen in simple pairwise competition models. In contrast, it was found that both the half-substrate constant and yield affected a guild's numerical dominance. Lower half-substrate constants and higher yields led to a guild accounting for a greater fraction of community biomass. This is not seen in simple pairwise competitions models where only yield affects final biomass. As a whole, the development of this model framework and the accompanying analyses have laid the groundwork for a new class of more detailed methanogen community models that go beyond the two compartment acetoclastic-hydrogenotrophic assumption. .