Understanding soil pore response to winter freeze-thaw

Freeze-thaw events disrupt soil pore structure, with implications for larger scale greenhouse gas fluxes and nutrient balance in winter and the growing season. Given its strong influence on soil C and N cycling, we need a better understanding of how pore structure is altered by freeze-thaw disturbances. Our objective was to investigate and quantify changes in the physical structure of soil, in response to experimental freeze-thaw disturbance. 

We collected intact soil cores from a northern hardwood forest in New Hampshire, USA. The soils were held at two contrasting water contents (low vs. high moisture) and then subjected to repeated freeze-thaw cycles in the laboratory, alternating between -10 °C and +4 °C. Soil porosity and pore network connectivity were determined during each freeze and thaw event using X-ray computed tomography (XCT) imaging. CO2 fluxes were measured continuously to track changes in microbial respiration following each disturbance. In addition, soil organic carbon was characterized using high resolution FTICR-MS to determine changes in the available C pool. This work links physical changes in soil structure to biogeochemical responses, highlighting the role of microsite scale processes on core-scale fluxes.