Development of microbial-enzyme-mediated decomposition model parameters through steady-state and dynamic analyses.

Area of Science:

• Soil Science
• Biogeochemistry
• Microbial Ecology

Background:

• Traditional soil organic matter (SOC) models often use simplified pools (fast/slow/passive).
• Understanding the detailed dynamics of physically defined SOC pools (particulate, mineral-associated, dissolved) is crucial for accurate climate change impact assessments.
• Microbial exoenzymes play a key role in decomposing SOC, but their specific dynamics are often simplified in models.

Purpose of the Study:

• To develop and validate a microbial-enzyme-mediated decomposition (MEND) model based on Michaelis-Menten kinetics.
• To investigate the impact of temperature changes on different SOC pools (POC, MOC, DOC) under varying carbon use efficiency (CUE) scenarios.
• To identify key model parameters influencing SOC dynamics using multi-objective parameter sensitivity analysis (MOPSA).

Main Methods:

• Developed the MEND model incorporating Michaelis-Menten kinetics for enzyme-mediated decomposition.
• Determined model parameter ranges and distributions using analytical steady-state and dynamic analyses with literature SOC data.
• Employed an improved multi-objective parameter sensitivity analysis (MOPSA) to identify critical parameters (microbial biomass maintenance, enzyme turnover/synthesis, CUE).

Main Results:

• A 2°C temperature increase led to increased POC-cellulose, MOC, and total SOC with dynamic CUE, but decreased them with constant CUE.
• Changes in POC, MOC, and total SOC pool sizes ranged from -8% to 8% under a +2°C scenario, irrespective of CUE type.
• Scenario analysis suggested higher temperatures with dynamic CUE could enhance POC-cellulose and MOC pool increases, reflecting specific enzyme-substrate interactions.

Conclusions:

• The MEND model demonstrates that microbial and enzyme dynamics significantly influence SOC pool responses to temperature changes.
• Dynamic CUE provides a more nuanced prediction of SOC pool responses compared to constant CUE under warming.
• Models incorporating fundamental microbial-enzyme principles offer qualitatively different and potentially more realistic simulation results than traditional SOC models.