Development of a lightweight, portable, waterproof, and low power stem respiration system for trees

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 (CO(2)) efflux (E(s)) is not commercially available resulting in limited observations based on the static method where air is recirculated through a stem enclosure. The static method has limited temporal resolution, suffers from condensation issues, requires a leak-free enclosure, which is often difficult to verify in the field, and requires physically removing the chamber or flushing it with ambient air before starting each measurement. • With the goal of improving our quantitative understanding of biophysical, physiological, biochemical, and environmental factors that influence diurnal E(s) patterns, here we present 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, eliminates the need for a pump to introduce air into the chamber, and water condensation issues by removing water vapor prior to CO(2) analysis. • Following a simple CO(2) infrared gas analyzer (IRGA) calibration and match procedure with a 400-ppm standard, we quantified diurnal E(s) observations over a 24-hours period during the summer growing season from an ash tree (Fraxinus sp.) in Fort Collins, Colorado. The results are consistent with previous laboratory and field studies that show E(s) can be suppressed during the day relative to the night.