Microbial-explicit processes and refined perennial plant traits improve modeled ecosystem carbon dynamics

Authors: BERARDI, DANIELLE - University Of Idaho; HARTMAN, MELANIE - Colorado State University; BRZOSTEK, EDWARD - West Virginia University; Bernacchi, Carl; DELUCIA, EVAN - University Of Illinois; VON HADEN, ADAM - University Of Wisconsin; KANTOLA, ILSA - University Of Illinois; MOORE, CAITLIN - University Of Western Australia; YANG, WENDY - University Of Illinois; HUDIBURG, TARA - University Of Idaho; PARTON, WILLIAM - Colorado State University

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2024
Publication Date: 3/11/2024
Citation: Berardi, D.M., Hartman, M.D., Brzostek, E.R., Bernacchi, C.J., DeLucia, E., von Haden, A.C., Kantola, I., Moore, C.E., Yang, W.H., Hudiburg, T.W., Parton, W.J. 2024. Microbial-explicit processes and refined perennial plant traits improve modeled ecosystem carbon dynamics. Geoderma. 443. Article 116851. https://doi.org/10.1016/j.geoderma.2024.116851.
DOI: https://doi.org/10.1016/j.geoderma.2024.116851

Interpretive Summary: Soils globally are significant storage houses for carbon, accounting for nearly half of what's stored in ecosystems. This vast reserve can either be released into the atmosphere, exacerbating climate change, or retained in the ground, mitigating its effects. A central issue has been our limited understanding of the intricate roles played by soil microbes in managing this carbon. To address this, we enhanced a scientific model, delving deeper into the influence of microbes, particularly in areas abundant with long-lived grasses. Using data from the mid-western U.S., we found that the refined model was notably more accurate in predicting carbon dynamics, especially during the colder months. This accomplishment is pivotal: by capturing the nuanced interactions of microbes and soil carbon, we're better equipped to forecast and respond to climate change challenges. This research not only underscores the importance of these tiny organisms but also paves the way for more informed environmental decision-making.

Technical Abstract: 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.