Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, ID 83844, USA; Wyoming Natural Diversity Database, University of Wyoming, Laramie, WY 82071, USA; Corresponding author at: Dept. 3381, 1000 E. University Ave., Laramie, WY 82071, USA.
Melannie D. Hartman
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA
Edward R Brzostek
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Biology, West Virginia University, Morgantown, WV, USA
Carl J. Bernacchi
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Global Change Photosynthesis Research Unit, USDA/ARS, Urbana, IL 61801, USA; Institute for Sustainability, Energy and Environment, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Evan H. DeLucia
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Institute for Sustainability, Energy and Environment, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Adam C. von Haden
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Plant and Agroecosystem Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA
Ilsa Kantola
Institute for Sustainability, Energy and Environment, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Caitlin E. Moore
School of Agriculture and Environment, The University of Western Australia, Crawley, WA 6009, Australia
Wendy H. Yang
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Institute for Sustainability, Energy and Environment, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
Tara W. Hudiburg
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, ID 83844, USA
William J. Parton
Center for Advanced Bioenergy and Bioproducts Innovation, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA
Globally, soils hold approximately half of ecosystem carbon and can serve as a source or sink depending on climate, vegetation, management, and disturbance regimes. Understanding how soil carbon dynamics are influenced by these factors is essential to evaluate proposed natural climate solutions and policy regarding net ecosystem carbon balance. Soil microbes play a key role in both carbon fluxes and stabilization. However, biogeochemical models often do not specifically address microbial-explicit processes. Here, we incorporated microbial-explicit processes into the DayCent biogeochemical model to better represent large perennial grasses and mechanisms of soil carbon formation and stabilization. We also take advantage of recent model improvements to better represent perennial grass structural complexity and life-history traits. Specifically, this study focuses on: 1) a plant sub-model that represents perennial phenology and more refined plant chemistry with downstream implications for soil organic matter (SOM) cycling though litter inputs, 2) live and dead soil microbe pools that influence routing of carbon to physically protected and unprotected pools, 3) Michaelis-Menten kinetics rather than first-order kinetics in the soil decomposition calculations, and 4) feedbacks between decomposition and live microbial pools. We evaluated the performance of the plant sub-model and two SOM cycling sub-models, Michaelis-Menten (MM) and first-order (FO), using observations of net ecosystem production, ecosystem respiration, soil respiration, microbial biomass, and soil carbon from long-term bioenergy research plots in the mid-western United States. The MM sub-model represented seasonal dynamics of soil carbon fluxes better than the FO sub-model which consistently overestimated winter soil respiration. While both SOM sub-models were similarly calibrated to total, physically protected, and physically unprotected soil carbon measurements, the models differed in future soil carbon response to disturbance and climate, most notably in the protected pools. Adding microbial-explicit mechanisms of soil processes to ecosystem models will improve model predictions of ecosystem carbon balances but more data and research are necessary to validate disturbance and climate change responses and soil pool allocation.
