The carbon dioxide leakage from chambers measured using sulfur hexafluoride

In plant chamber studies, if CO2 leaking from a chamber is not quantified, it can lead to an overestimate of assimilation rates and an underestimate of respiration rates; consequently, it is critical that CO2 leakage be determined. Sulfur hexafluoride (SF6) was introduced into the chambers as a tracer gas to estimate leakage rates. Chamber leakage constants were determined by measuring the rate of decline in SF6 concentration in the chambers. The leakage in the chambers occurs via pressure differences within the air handler rather than via diffusion through the Teflon film covering the chamber. Consequently, the leakage constant for CO2 is the same as for SF6, i.e. no adjustment for differences in molecular weight is required. The leakage rate for CO2 averaged 0.26 mmol m s at ambient CO2 and averaged 2.7 mmol m s at elevated CO2. The CO2 leak rate is essentially constant in the chambers despite a diurnally varying ambient concentration; chamber leakage was not correlated with changes in temperature, wind speed, dew point or atmospheric pressure. The results of this study show that SF6 can be used to estimate chamber leakage with precision and reproducibility and it can be used to estimate the leakage of CO2, H2O vapor and other gases of interest. The use of SF6 has the advantage of using a gas for measuring chamber leakage that is not involved in physiological processes. © 2000 Published by Elsevier Science B.V.