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

抄録

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.