Analysis of leakage in IRGA's leaf chambers of open gas exchange systems: quantification and its effects in photosynthesis parameterization

Abstract

The measurement of the response of net photosynthesis to leaf internal CO2 (i.e. A-Ci curves) is widely used for ecophysiological studies. Most studies did not consider CO2 exchange between the chamber and the surrounding air, especially at the two extremes of A-Ci curves, where large CO2 gradients are created, leading to erroneous estimations of A and Ci. A quantitative analysis of CO2 leakage in the chamber of a portable open gas exchange system (Li-6400, LI-COR Inc., NE, USA) was performed. In an empty chamber, the measured CO2 leakage was similar to that calculated using the manufacturer's equations. However, in the presence of a photosynthetically inactive leaf, the magnitude of leakage was substantially decreased, although still significant. These results, together with the analysis of the effects of chamber size, tightness, flow rate, and gasket material, suggest that the leakage is larger at the interface between the gaskets than through the gaskets. This differential leakage rate affects the parameterization by photosynthesis models. The magnitude of these errors was assessed in tobacco plants. The results showed that leakage results in a 10% overestimation of the leaf maximum capacity for carboxylation (Vc,max) and a 40% overestimation of day respiration (Rl). Using the manufacturer's equations resulted in larger, non-realistic corrections of the true values. The photosynthetic response to CO2 concentrations at the chloroplast (i.e. A-Cc curves) was significantly less affected by leakage than A-Ci curves. Therefore, photosynthetic parameterization can be improved by: (i) correcting A and Ci values for chamber leakage estimated using a photosynthetically inactive leaf; and (ii) using A-Cc instead of A-Ci curves.

Tracing Photosynthetic Response Curves with Internal CO₂ Measured Directly

“…For the open gas exchange system, the diffusion leak of CO2 was readily detected as the apparent 'net photosynthesis' at various CO2 concentrations (Flexas et al, 2007). Unexpectedly, there was only a marginal effect on leakage caused by the isolation of the cup from the open Environ.…”

“…We estimated diffusion molar flow rate of CO2 (KCO2) and water vapor (KH2O) according to Flexas et al (2007) and Rodeghiero et al (2007). Previous studies (Lauer and Boyer, 1992;Boyer and Kawamitsu, 2011) have preferentially used paraffin/-lanolin (P/L) coat to prevent diffusion leaks in the gas exchange systems.…”

“…The applicability of the system for A Ci curve measurement was tested in the sunflower (Helianthus annuus L.) leaf. We took special care to minimize bulk air flow through the leaf (Lauer and Boyer, 1992;Boyer and Kawamitsu, 2011), diffusion leaks (Flexas et al, 2007;Rodeghiero et al, 2007), and changes in the CO2 gradient across the leaf mesophyll (Mott and O'Leary, 1984;Parkhurst et al, 1988;Parkhurst and Mott, 1990) that can be important for the measurement.…”

Day and night respiration of three tree species in a temperate forest of northeastern China

“…Therefore, the respiration rate measured at low CO2 concentration was generally overestimated. A correction for leakage was necessary because it is hard to avoid CO2 exchange or leakage between the infrared gas analyzer (IRGA) chamber and the surrounding air (Pons & Welschen 2002, Shapiro et al 2004, Flexas et al 2007, Rodeghiero et al 2007). We corrected for CO2 leakage by diffusion in the Laisk method based on the following equation (eqn.…”

“…Some studies have proposed that the overestimation of RLL is caused by the CO2 acting as an inhibitor of certain enzymes (Brooks & Farquhar 1985, Kirschbaum & Farquhar 1987, Tjoelker et al 2001. However, a large number of studies suggest that leaf respiration changes with CO2 possibly due to small leaks or diffusion in the gas exchange measurement systems (Amthor et al 2001, Pons & Welschen 2002, Shapiro et al 2004, Flexas et al 2007, Rodeghiero et al 2007. Therefore, in this study RLL was corrected based on the method suggested by Li-Cor Inc (2004) to compensate the CO2 leakage in the Laisk method.…”