부산대학교 도서관

The barometric process separation (BaPS) technique is a well-established incubation method to simultaneously measure gross nitrification and respiration rates in soil. Its application, however, is still critical in soils with pH above 6.5. Here, a substantial part of microbial CO2production is retained in soil solution (CO2,aq) due to shifts in the carbonate equilibrium. This may lead to substantial errors in gas balance calculation. Yet, utilization of the BaPS technique is only reliable if the critical term is adequately quantified. We present an easy, inexpensive, and direct method, the sterilization-CO2-injection (SCI) method, to measure CO2retention during soil incubation. Sterilized soil was incubated in the BaPS system, and defined volumes of CO2were injected to stepwise increase CO2partial pressure (pCO2) inside the chamber and to analyse the physicochemical equilibration process. Five exemplary agricultural soils from Northeast China and Southwest Germany were used for method establishment, presenting pH values between 4.4 and 7.6 and carbonate contents between 0% and 3.9%. We observed that in soils with pH > 6.5, 70%–90% of the injected CO2was taken up by the soil until the equilibrium inside the chamber was re-established. As expected, in soils with low pH (< 6.5), measured CO2retention was low. CO2retention patterns were sensitive to incubation temperature with tri-fold dissolution capacity at 5 °C compared to 25 °C, but insensitive to variations in soil water content. The resulting soil-specific relationship between pCO2and CO2,aqconcentration allowed the quantification of CO2,aqconcentration as a function of headspace pCO2.