Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Model description paper
13 Feb 2018
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Geoscientific Model Development (GMD) and is expected to appear here in due course.
ORCHIMIC (v1.0), a microbe-driven model for soil organic matter decomposition designed for large-scale applications
Ye Huang1, Bertrand Guenet1, Philippe Ciais1, Ivan A. Janssens2, Jennifer L. Soong2,3, Yilong Wang1, Daniel Goll1, Evgenia Blagodatskaya4,5, and Yuanyuan Huang1 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
2University of Antwerp, Department of Biology, 2610 Wilrijk, Belgium
3Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
4Department of Agricultural Soil Science, University of Goettingen, Büsgenweg 2 37077 Göttingen, Germany
5Institute of Physicochemical and Biological Problems in Soil Science, 142290 Pushchino, Russia
Abstract. The role of soil microorganisms in regulating soil organic matter (SOM) decomposition is of primary importance in the carbon cycle, and in particular in the context of global change. Modelling soil microbial community dynamics to simulate its impact on soil gaseous carbon (C) emissions and nitrogen (N) mineralization at large spatial scales is a recent research field with the potential to improve predictions of SOM responses to global climate change. We here present a SOM model called ORCHIMIC whose input data that are consistent with those of global vegetation models. The model simulates decomposition of SOM by explicitly accounting for enzyme production and distinguishing three different microbial functional groups: fresh organic matter (FOM) specialists, SOM specialists, and generalists, while implicitly also accounting for microbes that do not produce extracellular enzymes, i.e. cheaters. This ORCHIMIC model and two other organic matter decomposition models, CENTURY (based on first order kinetics and representative for the structure of most current global soil carbon models) and PRIM (with FOM accelerating the decomposition rate of SOM) were calibrated to reproduce the observed respiration fluxes from FOM and SOM and their possible interactions from incubation experiments of Blagodatskaya et al. (2014). Among the three models, ORCHIMIC was the only one that captured well both the temporal dynamics of the respiratory fluxes and the magnitude of the priming effect observed during the incubation experiment. ORCHIMIC also reproduced well the temporal dynamics of microbial biomass. We then applied different idealized changes to the model input data, i.e. a 5 K stepwise increase of temperature and/or a doubling of plant litter inputs. Under 5 K warming, ORCHIMIC predicted a 0.002 K−1 decrease in the C use efficiency (defined as the ratio of C allocated to microbial growth to the sum of C allocated to growth and respiration) and a 3 % loss of SOC. Under the double litter input scenario, ORCHIMIC predicted a doubling of microbial biomass, while SOC stock increased by less than 1 % due to the priming effect. This limited increase in SOC stock contrasted with the proportional increase in SOC stock as modelled by the conventional SOC decomposition model (CENTURY), which cannot reproduce the priming effect. If temperature increased by 5 K and litter input is doubled, the model predicted almost the same loss of SOC as when only temperature was increased. These tests suggest that the responses of SOC stock to warming and increasing input may differ a lot from those simulated by conventional SOC decomposition models, when microbial dynamics is included. The next step is to incorporate the ORCHIMIC model into a global vegetation model to perform simulations for representative sites and future scenarios.
Citation: Huang, Y., Guenet, B., Ciais, P., Janssens, I. A., Soong, J. L., Wang, Y., Goll, D., Blagodatskaya, E., and Huang, Y.: ORCHIMIC (v1.0), a microbe-driven model for soil organic matter decomposition designed for large-scale applications, Geosci. Model Dev. Discuss.,, in review, 2018.
Ye Huang et al.
Ye Huang et al.

Model code and software

ORCHIMICv1.0 Y. Huang et al.
Ye Huang et al.


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Short summary
ORCHIMIC is an effort trying to improve the representation of SOC dynamics in Earth system models and has a structure that can be easily incorporated into CENTURY-based Earth system models. In ORCHIMIC, key microbial dynamics (i.e. enzyme production, enzymatic decomposition and microbial dormancy) are included. The ORCHIMIC model can reproduce observed temporal dynamic of respiration and priming effects and thus a better tool for climate projections and SOC responses prediction.
ORCHIMIC is an effort trying to improve the representation of SOC dynamics in Earth system...