Carbon Cycle: Belowground Biogeochemical Advances

Improved understanding of soil carbon cycling for prediction and management

Accurate understanding of soil processes is critical for predicting the role of soils in the global climate system, including terrestrial CO2 sinks and informing mitigation via bioenergy and proposed sequestration strategies. Currently, gaps in process-level understanding make prediction of ecosystem-climate feedbacks , as well as land-based mitigation, highly uncertain. Pathways and rates of soil carbon cycling are complex functions of climatic, abiotic, biotic, and landscape factors, making the emergent response of soils to perturbation dependent on myriad processes. As a result, the temporal evolution of ecosystem responses to warming or land use is difficult to predict.

The selected projects described here conduct basic research in biogeochemistry and ecosystem ecology, microbial ecology and genomics, geochemistry, and ecosystem modeling to address these gaps. We leverage the resulting improved understanding to develop mechanistic models that are applicable across spatial and temporal scales and to assess the roles of soils in global change. Our accomplishments include developing best-in-class biogeochemical models for Earth system models (ELMv1-ECA), field-scale agriculture (DroCam, ecosys), and fine-scale simulations (ecosys); novel experiments (e.g., whole soil warming); and data sets (e.g., radiocarbon). Our work has shown that soil carbon cycling is more responsive to warming than typically assumed and that the 21st-century terrestrial carbon sink is currently overestimated by many models.

Recent science & program advances

  • Established the longest-running whole-soil warming experiment and identified deep soil carbon responses to warming that imply positive feedbacks to climate change
  • This soil warming experiment indicates that deep subsurface soil carbon is vulnerable to warming of +4°C, commensurate with IPCC predictions for 2100, leading to a sustained increase in CO2 production from the whole soil profile and thus a significant loss of soil carbon
  • Developed mechanistic model treatments of soil organic carbon (SOC) dynamics for integration with land models, including effects of soil microbial mortality, moisture, and temperature
  • Used SOC radiocarbon observations to evaluate the 21st-century carbon sink, ELMv1, and methods for CMIP models
  • Identified high equifinality in laboratory methods used to infer SOC temperature sensitivity and proposed alternative approaches using microbe-explicit models. These results imply needed changes to global land models used to assess 21st- century climate change
  • High-latitude soils are predicted to have higher soil respiration losses over the 21st century, due to increased active layer depths, temperature, and C inputs but increased net primary production is expected to lead to a new sink
  • Synthesized observations and applied inventory models to simulate abrupt thaw impacts on permafrost carbon balance; our results indicate that abrupt thaw emissions are likely to offset the high-latitude carbon sink currently predicted by many land models

Relevant Projects


EESA benefits from rich partnerships with our collaborators and sponsors. See project & program links above for more information.

Publication Highlights

Soil Organic Matter Temperature Sensitivity Cannot Be Directly Inferred from Spatial Gradients. Global Biogeochemical Cycles, 2019

Comparison with Global Soil Radiocarbon Observations Indicates Needed Carbon Cycle Improvements in the E3SM Land Model. Journal of Geophysical Research: Biogeosciences, 2019

Density-Dependent Microbial Turnover Improves Soil Carbon Model Predictions of Long-Term Litter Manipulations. 19th EGU General Assembly, 2017

Radiocarbon Constraints Imply Reduced Carbon Uptake by Soils during the 21st Century. Science, 2016

The Whole-Soil Carbon Flux in Response to Warming. Science, 2017

21st Century Tundra Shrubification Could Enhance Net Carbon Uptake of North America Arctic Tundra under an RCP8.5 Climate Trajectory. Environmental Research Letters, 2018

Accelerated Nutrient Cycling and Increased Light Competition Will Lead to 21st Century Shrub Expansion in North American Arctic Tundra. Journal of Geophysical Research: Biogeosciences, 2018

Mathematical Reconstruction of Land Carbon Models from Their Numerical Output: Computing Soil Radiocarbon from12C Dynamics. Journal of Advances in Modeling Earth Systems, 2019

CMIP5 Models Predict Rapid and Deep Soil Warming Over the 21st Century. Journal of Geophysical Research: Biogeosciences, 2020

A Theory of Effective Microbial Substrate Affinity Parameters in Variably Saturated Soils and an Example Application to Aerobic Soil Heterotrophic Respiration. Journal of Geophysical Research: Biogeosciences, 2019

Linear Two-Pool Models Are Insufficient to Infer Soil Organic Matter Decomposition Temperature Sensitivity from Incubations. Biogeochemistry, 2020

Carbon Release through Abrupt Permafrost Thaw. Nature Geoscience, 2020

Permafrost Collapse Is Accelerating Carbon Release. Nature, 2019

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