Developing a high-latitude soil carbon cycle model with a focus on trait-based representation of decomposition

Background/Question/Methods

Global climate change is projected to have a significant impact on high-latitude ecosystems by altering the stability and distribution of annual permafrost and deepening the active layer. High-latitude permafrost soils store large quantities of organic matter, and climate change may lead to increases in organic matter decomposition and the production of carbon dioxide (CO₂). The magnitude of CO₂ flux depends largely on a complex suite of mechanisms primarily regulated by C-cycling microorganisms. In the present study we are developing a mechanistic ecological model by synthesizing multiple microbial traits to reconstruct a representation of the heterotrophic microbial community. The model develops a dynamic energy budget that is scaled against the availability and identity of electron donors and acceptors and represented by an ATP pool. This energy budget contributes to regulating macromolecular synthesis, including exoenzyme production, cell growth, and division. Traits encoded by a hypothetical ‘genome’ that are specific to individual guilds include growth rate, carbon use efficiency (CUE), and the possession of between 2 and 11 distinct monomer transporters linked to the presence of exoenzymes within the ‘genome’. These traits determine the emergence of microbial communities under initial environmental conditions and also community dynamics as conditions change over time. The model prognoses decomposition rates, carbon pool transformations, and CO₂ production. 

Results/Conclusions

The system ecology was initially studied using a chemostat approach with one or multiple polymeric substrates. Emergence of the heterotrophic community was dependent on the presence of different polymers and trade-offs between physiological traits (e.g., possession of different exoenzymes or growth rate) and the cellular energy budget.  Using this approach we examine the dynamics of the heterotrophic community and identify conditions under which copiotrophic and oligotrophic communities dominate. Competition between these groups resulted in differences in decomposition and CO₂ production rates on spatial and temporal scales as communities changed. We discuss model predictions under anticipated future climate change scenarios (e.g., increased N-deposition, temperature, and permafrost thaw) to evaluate the role climate driven microbial dynamics might play in future greenhouse gas production.