PNNL

The Science

Biogeochemists and ecologists widely measure soil respiration, the flow of carbon dioxide (CO₂) from the soil to the atmosphere generated by both plant roots and microbes, and one of the largest fluxes of carbon in the Earth system. Researchers make these measurements under very different conditions (different instruments, methods, times of day, etc.) with a limited understanding of how these differences affect the subsequent calculations of soil respiration fluxes. As any biases would propagate up to global carbon flux estimates, researchers used a database of flux measurements and found no significant biases in the final data.

The Impact

This study is the first to leverage a global database of flux estimates and measurement conditions to assess potential biases in flux data induced by different measurement techniques. This work tested data obtained via a range of techniques, with none of the factors explored imparting a large bias to the subsequent flux estimates. This means that the current understanding of how much carbon flows from the soil to the atmosphere every year is likely robust and not unduly skewed by the many different approaches used by scientists worldwide.

Summary

Soil‐to‐atmosphere CO₂ is the second largest component of the terrestrial carbon cycle and researchers’ ability to balance the terrestrial carbon budget and forecast climate change relies upon accurate measurements of this process. Researchers commonly use collars permanently installed in the soil to measure soil‐to‐atmosphere CO₂. However, differences in collar properties, measurement duration, and measurement frequency could lead to biases in the estimation of the amount of annual soil‐to‐atmosphere CO₂. While many methodological studies for measuring soil‐to‐atmosphere CO₂ exist, there have been no comprehensive evaluations of the influence of collar properties and measurement duration on annual soil‐to‐atmosphere CO₂ variability. This study used a global data set to analyze soil‐to‐atmosphere CO₂ measurements to look for biases related to collar properties and measurement duration. The annual amount of soil‐to‐atmosphere CO₂ negatively correlated with collar height and insertion depth, but showed no significant relationship to measurement duration and measurement frequency. Overall, the analysis showed no significant bias based on collar properties and measurement duration. These results provide strong support for compiling site‐scale soil‐to‐atmosphere CO₂ measurements to support synthesis analyses, global soil‐to‐atmosphere CO₂ modeling, and global soil‐to‐atmosphere CO₂ benchmarking.

PNNL Contact

Vanessa Bailey, Pacific Northwest National Laboratory, Vanessa.Bailey@pnnl.gov 

Funding

This research was supported by the U.S. Department of Energy, Office of Science, Biological and Environmental Research program as part of the Terrestrial Ecosystem Sciences Program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute.