Development of chamber-based sampling technique for determination of carbon stable isotope ratio of soil respired CO2 and evaluation of influence of CO2 enrichment in chamber headspace

Abstract

We developed an experimental method for precise determination of carbon stable isotope ratio (δ13C) of soil-respired CO2 under natural condition. We devised a flask sampling system optimized for collecting soil-respired CO2 to minimize the measurement artifacts related to pressure anomaly. The δ13C of soil-respired CO2 was estimated from relationship between change rates of the CO2 mole fraction and the δ13C of the CO2 in a closed chamber at the soil surface by using two end-member simple mixing model. We tested the influence of CO2 enrichment in the soil-chamber headspace on the estimates of the δ13C of soil respired CO2 by using high-precision measurements of CO2 mole fraction and δ13C. To our results, the estimates of the δ13C of soil respired CO2 was rather insusceptible to the influence of the CO2 enrichment in the chamber as compared with the soil CO2 efflux. Improvement of analytical precision of δ13C is preferred approach to reduce the error in the estimates of δ13C of soil respired CO2. On the other hand, extending the sampling range of CO2 mole fraction in the chamber can be cost-effective means for the error-reduction practically.