05 Oct 2023
 | 05 Oct 2023

Modeling boreal forest soil dynamics with the microbially explicit soil model MIMICS+ (v1.0)

Elin Ristorp Aas, Heleen A. de Wit, and Terje Koren Berntsen

Abstract. Understanding carbon exchange processes between land reservoirs and the atmosphere is essential for predicting carbon-climate feedbacks. Still, considerable uncertainty remains in the representation of the terrestrial carbon cycle in Earth System Models. An emerging strategy to constrain these uncertainties is to include the role of different microbial groups explicitly. Following this approach, we extend the framework of the MIcrobial-MIneral Carbon Stabilization (MIMICS) model with additional mycorrhizal groups and a nitrogen cycle that includes a novel representation of inorganic nitrogen sorption to particles via a Langmuir isotherm. MIMICS+ v1.0 is designed to capture and quantify relationships between soil microorganisms and their environment, with a particular emphasis on boreal ecosystems. We evaluated MIMICS+ against podzolic soil profiles in Norwegian forests as well as the conventional Community Land Model (CLM). MIMICS+ matched observed carbon stocks better than CLM, and gave a broader range of C:N ratios, more in line with observations. This is mainly explained by a higher direct-plant-derived fraction into the Soil Organic Matter (SOM) pools. The model produces microbial biomass estimates in line with numbers reported in the literature. MIMICS+ also showed better representation of climate gradients than CLM, especially in terms of temperature. To investigate responses to changes in nutrient availability, we performed an N enrichment experiment, and found that nitrogen sorbed to particles through the sorption algorithm served as a long-term storage of nutrients for the microbes. Furthermore, although the microbial groups responded considerably to the nitrogen enrichment, we only saw minor responses for carbon storage and respiration. Together, our results present MIMICS+ as an attractive tool for further investigations of interactions between microbial functioning and their (changing) environment.

Elin Ristorp Aas et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2069', Anonymous Referee #1, 22 Oct 2023
  • RC2: 'Comment on egusphere-2023-2069', Anonymous Referee #2, 18 Nov 2023

Elin Ristorp Aas et al.

Model code and software

MIMICSplus Elin Ristorp Aas

Elin Ristorp Aas et al.


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Short summary
By including microbial processes in soil models, we learn about how the soil system interacts with its environment, and responds to climate change. We present a soil process model, MIMICS+, able to reproduce carbon stocks found in boreal forest soils better than a conventional land model. With the model we also found that when adding nitrogen, the relationship between soil microbes changed notably. Coupling the model to a vegetation model, will allow further investigation of these mechanisms.