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 C[O.sub.2] enriched air. which was monitored by an infrared gas analyzer (IRGA). When the internal C[O.sub.2] concentration within the reservoir was elevated, diffusion rates through the porous medium were measured by recording changes in C[O.sub.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 C[O.sub.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 C[O.sub.2] concentrations.