A Novel Laboratory Method to Realistically Simulate Freeze-Thaw Conditions and Nitrous Oxide Emissions.

Field experiments are essential for demonstrating the importance of freeze-thaw (FT) induced nitrous oxide (N₂O) emissions under real-world conditions, yet results are often variable due to fluctuating environmental conditions and difficulties characterizing simultaneous soil chemical properties. Laboratory studies, in contrast, are useful for gaining process-level understanding of soil processes because environmental conditions can be controlled. However, simulating real-world FT conditions in a laboratory setting is challenging and previous laboratory studies targeting N₂O production from soils have been unrealistic (i.e. unrealistic minimum temperatures, freezing rates, direction of freezing in lab studies being omni-directional rather than uni-directional, lack of snow, and lack of interface between frozen and unfrozen soil). In this study, a novel method to realistically simulate FT conditions in a laboratory environment was developed, and its effects on N₂O emissions were evaluated. The new method allowed for the ability to control intensity, extent, direction and duration of freeze and thaw of soils. The simulation system involved utilizing intact undisturbed soil cores placed within a lidless Styrofoam cooler filled with soil. A heating pad coupled to a temperature controlled outlet was placed beneath the cooler to ensure that soil at 20-25 cm stayed above 0°C, as soils rarely freeze at these depths. The rate at which soil cooled for the simulation system at 5cm (-0.021°C h^-1), was similar to field measurements (-0.025°C h^-1) and the rate at which soil thawed for the simulation system (+0.030°C h^-1) was also similar to field measurements (+0.026°C h^-1). We conclude that this simulation method allows for the manipulation of unidirectional FT in soil cores to allow for future rapid testing of N₂O emissions and related processes that are significantly affected by FT processes.