Browsing by Subject "Gross nitrification"

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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.
Nitrogen dynamics of grassland soils with differing habitat quality: high temporal resolution captures the details
(2023) Kukowski, Sina; Ruser, Reiner; Piepho, Hans‐Peter; Gayler, Sebastian; Streck, Thilo
Excessive nitrogen (N) input is one of the major threats for species‐rich grasslands. The ongoing deterioration of habitat quality highlights the necessity to further investigate underlying N turnover processes. Our objectives were (1) to quantify gross and net rates of mineral N production (mineralization and nitrification) and consumption in seminatural grasslands in southwest Germany, with excellent or poor habitat quality, (2) to monitor the temporal variability of these processes, and (3) to investigate differences between calcareous and decalcified soils. In 2016 and 2017, gross N turnover rates were measured using the 15N pool dilution technique in situ on four Arrhenatherion meadows in biweekly cycles between May and November. Simultaneously, net rates of mineralization and nitrification, soil temperature, and moisture were measured. The vegetation was mapped, and basic soil properties were determined. The calcareous soils showed higher gross nitrification rates compared with gross mineralization. In contrast, nitrification was inhibited in the decalcified soils, most likely due to the low pH, and mineralization was the dominant process. Both mineralization and nitrification were characterized by high temporal variability (especially the former) and short residence times of N in the corresponding pools (<2 days) at all sites. This illustrates that high temporal resolution is necessary during the growing season to detect N mineralization patterns and capture variability. Parallel determination of net N turnover rates showed almost no variability, highlighting that net rates are not suitable for drawing conclusions about actual gross turnover rates. During the growing season, the data show no clear relationship between soil temperature/soil moisture and gross N turnover rates. For future experiments, recording of microbial biomass, dissolved organic matter, and root N uptake should be considered.