Soil freeze–thaw cycle experiments: Trends, methodological weaknesses and suggested improvements

Although freeze–thaw cycles can alter soil physical properties and microbial activity, their overall impact on soil functioning remains unclear. This review addresses the effects of freeze–thaw cycles on soil physical properties, microorganisms, carbon and nutrient dynamics, trace gas losses and higher organisms associated with soil. I discuss how the controlled manipulation of freeze–thaw cycles has varied widely among studies and propose that, despite their value in demonstrating the mechanisms of freeze–thaw action in soils, many studies of soil freeze–thaw cycles have used cycle amplitudes, freezing rates and minimum temperatures that are not relevant to temperature changes across much of the soil profile in situ. The lack of coordination between the timing of soil collection and the season for which freeze–thaw cycles are being simulated is also discussed. Suggested improvements to future studies of soil freeze–thaw cycles include the maintenance of realistic temperature fluctuations across the soil profile, soil collection in the appropriate season and the inclusion of relevant surface factors such as plant litter in the fall or excess water in the spring. The implications of climate change for soil freeze–thaw cycles are addressed, along with the need to directly assess how changes in soil freeze–thaw cycle dynamics alter primary production.