Impact of soil freezing and thawing dynamics on greenhouse gas emission and nutrient fluxes

English Abstract:

Freezing and thawing is an abiotic stress applied to soils that affect the physical properties, biogeochemistry, microbial activity, and the rates of carbon and nitrogen cycling in soils. A better mechanistic understanding of how freezing and thawing influences soil respiration, greenhouse gas emissions, and leaching of nutrients to groundwater is needed to predict how soils will respond to climate change. To enhance this understanding, a highly instrumented soil column experiment was designed to realistically simulate freeze-thaw dynamics under controlled conditions. This approach combines the acquisition of integrated physical, chemical and microbial data collected periodically from different depths in which time-dependent, vertical temperature profiles are generated that mimic temperature distributions in real soils under freeze-thaw conditions. In this presentation, we focus on soil-specific physical, chemical, microbial factors (e.g. redox conditions, respiration, fermentation) and the mechanisms that drive greenhouse gases emission and nutrient cycling in soils under freeze-thaw cycles. The results indicate that changes in the soil microbial community and activity, driven by the fluctuations in temperature and oxygen availability, together with the recurrent development of a physical barrier preventing exchange of gaseous compounds between the soil and atmosphere during freezing conditions, modulate the time-dependent release of greenhouse gases from the soil surface. In other words, both physical and biogeochemical processes regulate the belowground soil carbon and nitrogen allocation and respiration during the alternating frost and thaw periods.