Explicit representation of microbes, enzymes, mineral surfaces, and isotopic tracers helps explain soil organic carbon decomposition and priming

Abstract:

Increased plant carbon inputs from CO₂ fertilization could accelerate native soil organic carbon (SOC) decomposition through the priming effect. Although this increase in SOC turnover rate due to priming might have important consequences for SOC dynamics, there are large uncertainties in the sign and magnitude of priming, as well as large challenges in identifying underlying mechanisms. Current SOC models, mostly based on first-order decomposition representations, do no represent many important biotic and abiotic processes, including the priming effect. The incorporation of explicit biotic and abiotic interactions in modeling SOC decomposition may improve our ability to accurately predict SOC dynamics.

In this study, we (1) develop a microbe-explicit SOC decomposition model to simulate SOC turnovers and priming and (2) test the model with a soil incubation experiment with ¹⁴C-labeled glucose addition. We report (1) the evolutions of modeled carbon pools, (2) the fate of ¹⁴C labeled glucose addition, (3) the model performance compared to observations, (4) the transient behavior of priming components, and (5) an analysis of the effects of carbon input magnitudes and frequencies on the priming effect.

Here are some findings from our model-experiment analyses: (1) the inclusion of an extracellular oxidative metabolism (EXOMET) in addition to intracellular microbial respiration helps improve the model performance; (2) priming is dominated by intracellular microbial respiration at the beginning of incubation (~ first 5 days) but later on dominated by EXOMET, which explains observed long-term sustaining priming; (3) the varying magnitudes of glucose addition do not change the magnitude of priming per unit addition; (4) the varying frequencies of glucose addition change the magnitude of priming per unit addition, but with contrast changing patterns for non-steady-state and steady state simulations; (5) constant annual total glucose addition shift the system to another steady state (saturated priming), while rising annual addition supports a long-term sustaining priming; (6) priming per unit glucose addition in non-steady-state simulations is much larger than that in steady-state simulations.