Soil-borne nitrous oxide (N2O) emissions have a high spatial and temporal variability which is commonly attributed to the occurrence of hotspots and hot moments for microbial activity in aggregated soil. Yet there is only limited information about the biophysical processes that regulate the production and consumption of N2O on microscopic scales in undisturbed soil. In this study, we introduce an experimental framework relying on simplified porous media that circumvents some of the complexities occuring in natural soils while fully accounting for physical constraints believed to control microbial activity in general and denitrification in particular. We used this framework to explore the impact of aggregate size and external oxygen concentration on the kinetics of O2 consumption, as well as CO2 and N2O production. Model aggregates of different sizes (3.5 vs. 7 mm diameter) composed of porous, sintered glass were saturated with a defined growth medium containing roughly 109 cells ml-1 of the facultative anaerobic, nosZ-deficient denitrifier Agrobacterium tumefaciens with N2O as final denitrification product and incubated at five different oxygen levels (0-13 vol-%). We demonstrate that the onset of denitrification depends on the amount of external oxygen and the size of aggregates. Smaller aggregates were better supplied with oxygen due to...
Agrobacterium Tumefaciens ; Anoxic Aggregate Centers ; Denitrification Kinetics ; Greenhouse Gas Emissions ; Microbial Hotspots ; Microsites ; Physically-Based Modeling ; Dewey Decimal Classification::300 | Sozialwissenschaften, Soziologie, Anthropologie::330 | Wirtschaft::333 | Boden- Und Energiewirtschaft::333,7 | Natürliche Ressourcen, Energie Und Umwelt
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