Implications of representing microbial physiology in soil C projections across scales

Background/Question/Methods

Projecting biogeochemical responses to global environmental change requires multi-scaled perspectives and draw on insight across scientific disciplines. Soil microbes, the drivers of soil organic matter decomposition and stabilization, remain notably absent from models used to project carbon (C) cycle–climate feedbacks. Here, we advance the MIcrobial-MIneral Carbon Stabilization (MIMICS) model.  MIMICS is a process-based soil biogeochemical model that explicitly represents the activity and diversity of microbial functional types. Thus, MIMICS provides a tool to investigate microbial community vs. soil mineralogy controls over soil organic matter dynamics in the context of environmental change. 

Results/Conclusions

Initial simulations indicate that MIMICS better represents global steady state soil C pools than the all of the models represented in the Intergovernmental Panel on Climate Change 5^th Assessment Report. The response of these simulated soil C pools to environmental change, however, strongly depends on assumptions made about microbial physiological response to perturbations.  For example, theory and observations suggest that nitrogen (N) enrichment influences microbial physiology, microbial community composition, and soil C storage. MIMICS allows us to start evaluating the proximate drivers of these responses. Preliminary results suggest that shifts in microbial growth efficiency (MGE) may be responsible for observed microbial and biogeochemical changes in response to N enrichment- but that direct measurements of MGE in soils may not confirm the mechanism we propose here.