A CARBON DIOXIDE FLUX GENERATOR FOR TESTING INFRARED GAS ANALYZER‐BASED SOIL RESPIRATION SYSTEMS

An artificial flux generation device was developed to test the accuracy of a closed‐dynamic soil respiration system (LICOR 6400). The device consisted of an enclosed reservoir with a porous top; the reservoir contained a volume of CO 2 enriched air, which was monitored by an infrared gas analyzer (IRGA). When the internal CO 2 concentration within the reservoir was elevated, diffusion rates through the porous medium were measured by recording changes in CO 2 concentration within the reservoir. This diffusion‐based artificial flux mimics natural soil respiration, and allows an independent verification of the accuracy of soil respiration measurement systems. We tested a LI‐COR 6400 portable photosynthesis system fitted with a 6400‐09 soil CO 2 flux chamber. On average, this system overestimated high flux rates by 2 to 4% and underestimated low flux rates by 4 to 20% over five independent trials. Soil respiration appeared to be sensitive to boundary layer mixing, and ambient CO 2 concentrations.