Sampling soil-derived CO₂ for analysis of isotopic composition: a comparison of different techniques

Abstract

A new system for soil respiration measurement [P. Rochette, L.B. Flanagan, E.G. Gregorich. Separating soil respiration into plant and soil components using analyses of the natural abundance of carbon-13. Soil Sci. Soc. Am. J., 63, 1207–1213 (1999).] was modified in order to collect soil-derived CO₂ for stable isotope analysis. The aim of this study was to assess the suitability of this modified soil respiration system to determine the isotopic composition (δ¹³C) of soil CO₂ efflux and to measure, at the same time, the soil CO₂ efflux rate, with the further advantage of collecting only one air sample. A comparison between different methods of air collection from the soil was carried out in a laboratory experiment. Our system, as well as the other dynamic chamber approach tested, appeared to sample the soil CO₂, which is enriched with respect to the soil CO₂ efflux, probably because of a mass dependent fractionation during diffusion and because of the atmospheric contribution in the upper soil layer. On the contrary, the static accumulation of CO₂ into the chamber headspace allows sampling of δ¹³C-CO₂ of soil CO₂ efflux.

Keywords:

• Carbon-13
• Carbon dioxide
• Measurement
• Respiration
• Sampling
• Soil

Acknowledgements

The work was financially supported by the European Commission through the MIND project, by the Italian MIUR through the Interlink programme and by the Regione Campania (Italy) through the INNOVA project.