The Science

Stem respiration is a quantitatively important but poorly understood component of ecosystem carbon cycling in terrestrial ecosystems. However, a dynamic stem gas exchange system for quantifying real-time stem carbon dioxide (CO₂) efflux (E_s) is not commercially available, resulting in limited observations using the static method. The static method has limited temporal resolution, suffers from condensation issues, requires a leak-free enclosure that is difficult to verify in the field, and requires physically removing or flushing the chamber between measurements. In this study, researchers present a custom system design for real-time off-the-grid monitoring of stem CO₂ E_s from diverse tropical forests.

The Impact

This method allows for real-time stem CO₂ E_s measurements to evaluate diurnal patterns of growth and respiration in hyperdiverse forests to help resolve major uncertainties surrounding stem respiration. While temperature is assumed to stimulate growth and its associated respiratory processes, preliminary real-time diurnal data collected with the technique suggest that plant hydraulics are also key, with midday water stress in the dry season limiting plant growth and respiratory process. Deployment of the techniques to remote tropical forests in Brazil will link plant hydraulics and carbon metabolism in ecosystem demographics models like the Functionally Assembled Terrestrial Ecosystem Simulator (FATES).

Summary

To improve quantitative understanding of biophysical, physiological, biochemical, and environmental factors that influence diurnal CO₂ E_s patterns, researchers created a custom system for quantifying real-time stem E_s in remote tropical forests. The system is low cost, lightweight, and waterproof with low power requirements (1.2-2.4 W) for real-time monitoring of stem E_s using a 3D-printed dynamic stem chamber and a 12V car battery. The design offers control over the flow rate through the stem chamber and eliminates the need for a pump to introduce air into the chamber and water condensation issues by removing water vapor prior to CO₂ analysis. Following a simple CO₂ infrared gas analyzer calibration and match procedure with a 400-ppm standard, researchers quantified diurnal E_s observations over a 24-hour period during the summer growing season from an ash tree in Fort Collins, Colo. Great success was achieved with this system in the Amazon during the rainy season in 2022. The results are consistent with previous laboratory and field studies that show E_s can be suppressed during the day relative to the night.

Principal Investigator

Kolby Jardine
Lawrence Berkeley National Laboratory
kjjardine@lbl.gov

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
brian.benscoter@science.doe.gov

Funding

Support for this research was provided as part of the Next-Generation Ecosystem Experiments Tropics (NGEE Tropics) funded by the U.S. Department of Energy’s (DOE) Office of Science, Biological and Environmental Research (BER) program through contract No. DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory (LBNL) as part of DOE’s Environmental System Science program. Support was also received from Christina Wistrom at the University of California–Berkeley Oxford Tract Greenhouse where the method was developed and Bryan Taylor at LBNL for computer systems and software.

References