Browsing by Subject "Respiratory quotient"

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Improvement of the Barometric Process Separation (BaPS) technique to measure microbial C and N transformation rates in arable high-pH soils
(2023) Munz, Hannah; Streck, Thilo
The Barometric Process Separation (BaPS) technique provides a simple way to determine the rates of heterotrophic microbial respiration, gross nitrification and denitrification in soils by crossbalancing CO2 and O2 production and consumption rates in a closed incubation system via gas balances. The BaPS measuring system has some methodological limitations, especially in soils of pH above 6.5. In these soils, the CO2 balance of the incubation system is strongly influenced by abiotic fluxes driven by thermodynamic equilibration of the CO2 - carbonate system of the soil solution, i.e. a non-negligible fraction of CO2 produced via respiration is buffered by the soil solution. Correct quantification of this flux is necessary to correctly determine the microbial process rates. It has been shown that the thermodynamic calculation of CO2 dissolution does not deliver accurate results, leading to uncertainty in and considerable over- and underestimations of the microbial process rates. In this dissertation, this problem has been solved by developing a method to experimentally determine abiotic CO2 buffering, the Sterilization-CO2-Injection (SCI) method. Moreover, the soil specific adaptation of the Respiratory Quotient (RQ) has been studied in detail in order to reestablishes the advantage of the BaPS of operating isotope-free. Furthermore, in this dissertation we present an easy on-site calibration method for the BaPS sensor set in order to garantee optimal data quality although the maintenance service by the manufacturer has been canceled. Overall, the presented adaptations and improvements enhance the accuracy of BaPS measurements and might enhance its value as a tool for measuring gross nitrification rates in the future.