Microbial physiology regulates long-term soil carbon and nitrogen stoichiometry

Background/Question/Methods

Soil carbon (C) and nitrogen (N) stoichiometry is a key indicator of the coupled soil C and N cycles, and its balance has important implications for maintaining ecosystem functioning and adapting to climate change. A line of evidence confirms that soil microbial community plays a crucial role in global biogeochemical cycles by regulating ecosystem processes such as soil organic matter decomposition, soil C sequestration, and nutrient cycling. Although an increasing number of ecosystem models have incorporated microbial processes, they primarily focus on soil C processes and stabilization, whereas the mechanism underlying the stabilization of soil C-N stoichiometry remains little explored. Here, we attempt to fill this gap by proposing a new model parameterization strategy that accounts for both short- and long-term model behaviors. We tested this idea using the latest C-N coupled Microbial-ENzyme Decomposition (MEND) model with field experimental data from a subtropical broadleaf forest ecosystem.

Results/Conclusions

The results of model parameter calibration showed that the simulated steady-state soil C:N ratio was overestimated as 21.1 ± 0.2 mg C mg–1 N when only short-term constraints were considered and 14.5 ± 0.2 mg C mg–1 N, consistent with the observations, when long-term constraints were added. Further analysis show that microbial physiology plays an important role in the long-term stability of soil C-N stoichiometry. Specifically, microbial use efficiencies of C and N are key mechanisms for regulating soil C:N ratios. We suggest that the parameterization of microbial ecological models should consider both short- and long-term model behaviors to ensure more realistic representation microbially-mediated soil biogeochemistry processes. This experimental-model integration study contributes to an enhanced understanding of the microbial regulatory mechanisms of soil C-N cycles.