The Science

Currently, soil carbon models that explicitly represent microbial activity have large biases in predicted carbon stocks and temporal dynamics. Scientists at Lawrence Berkeley National Laboratory have showed that accounting for density-dependent microbial mortality greatly improves predictions against long-term observations and improves microbial models for inclusion in Earth system models (ESMs).

The Impact

The proposed model modification addresses a long-standing problem in mechanistic models of soil biogeochemistry and improves predictions of soil carbon storage in response to long-term changes in plant productivity.

Summary

Changes in climate, atmospheric composition, and land use all have the potential to alter plant inputs to soil in ways that impact soil microbial activity. Many microbial models of soil organic carbon (SOC) decomposition have been proposed recently to advance prediction of SOC dynamics. Most of these models, however, exhibit unrealistic oscillatory behavior, and their SOC stocks are insensitive to long-term changes in carbon inputs. U.S. Department of Energy (DOE) national laboratory scientists diagnosed the source of these problems in four archetypal microbial models and proposed a density-dependent formulation of microbial turnover, motivated by community-level interactions, that limits population sizes and reduces oscillations. They compared model predictions to 24 long-term carbon-input field manipulations and identified key benchmarks. The proposed formulation reproduces soil carbon responses to long-term carbon-input changes and implies greater SOC storage associated with CO₂ fertilization–driven increases in carbon inputs over the coming century compared to recent microbial models. This study provides a simple, yet effective, modification to improve microbial models for inclusion in ESMs.

Principal Investigator

Margaret Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This material is based on work supported by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-05CH11231.

References