Submitted to: Environmental and Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2003
Publication Date: 8/4/2003
Citation: Baker, J.T., Kim, S., Gitz, D.C., Timlin, D.J., Reddy, V. 2003. Estimating carbon dioxide leakage rates in controlled environment chambers using nitrous oxide. Environmental and Experimental Botany. 51:103-110. Interpretive Summary: In order to grow, crop plants use sun light to take carbon dioxide out of the air in a process called `photosynthesis¿. Scientists who study photosynthesis of crop plants often use outdoor, naturally sunlit, plant growth chambers that can monitor the amount of carbon dioxide that plants take out of the chamber atmosphere. Because these chambers often leak air containing carbon dioxide, it is necessary to accurately measure this leakage rate. In this experiment we tested the ability of our chambers to accurately measure carbon dioxide leakage rates by measuring the leakage rate of another gas called nitrous oxide. Nitrous oxide is inert and in no way harms the plants during experiments in these chambers. We found that we could very accurately calculate how much carbon dioxide leaked out of our chambers by measuring the rate that nitrous oxide was lost from the chambers. This method provides a fast and easily repeatable way of correcting our photosynthesis measurements for carbon dioxide that leaks from our chamber system.
Technical Abstract: Naturally sunlit, outdoor controlled-environment chambers provide an important research tool for studying the effects of environmental variables on crop physiological processes. Typically 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 recently installed 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 CO2 drawdown method (CL) were compared with CO2 leakage rates determined using N2O as a tracer gas (CLN). 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 SPAR (Soil-Plant-Atmosphere-Research) chambers. Comparisons of CL with CLN indicated that CLN was an excellent predictor of CL. However, the analysis did show a slight but consistent overestimation of CL by CLN that averaged 0.3, 1.4 and 1.1 µmols (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 CO2 treatment set points that make estimation of CL difficult.