A method for estimating carbon dioxide leakage rates in controlled-environment chambers using nitrous oxide

Naturally sunlit, outdoor controlled-environment chambers provide an important research tool for studying the effects of environmental variables on crop physiological processes. Topically these types of chambers are semi-closed and are capable of continuously monitoring canopy scale gas exchanges. Accurately determining chamber CO2 leakage rate is essential for correcting measurements of photosynthesis and respiration in these kinds of chambers. The purpose of this study was to evaluate the ability of a new CO2 leak quantification system which used N2O as a tracer gas to estimate chamber CO2 leakage rates in a recently constructed outdoor, controlled-environment chamber facility at Beltsville, MD. Chamber CO2 leakage rates as determined by the loss of CO2 (C-L) from the chamber were compared with CO2 leakage rates determined using N2O as a tracer gas (C-LN). These two methods of determining leakage rates were compared in two different types of chambers: smaller and more tightly sealed Daylit chambers and larger more leaky Soil-Plant-Atmosphere-Research (SPAR) chambers. Comparisons of C-L with C-LN indicated that CLN was an excellent predictor of CL. However, over a wide range of internal to external concentration gradients, the analysis did show a slight but consistent overestimation of C-L by C-LN that averaged 0.3, 1.4, and 1.1 mumol CO2 m(-2) s(-1) for the Daylit chambers, the SPAR chambers and all data combined, respectively. These results indicate that N2O can be used as a tracer gas to accurately and reliably estimate chamber CO2 leakage rates in real time during experiments in the presence of plants and when it is necessary to maintain specific chamber C02 treatment set points that make estimation of CL difficult. Published by Elsevier B.V.