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