Influences of forest cover on soil freeze-thaw dynamics and greenhouse gas emissions through the regulation of snow regimes: A comparison study of the farmland and forest plantation

Vegetation cover has implications for seasonally frozen soil dynamics and greenhouse gas emissions. We examined the frozen soil dynamics and N2O and CO2 efflux in a forest plantation (Populus ssp.) and farmland. The experiments were carried out at a forest reclamation site in Zhangbei county, Hebei province, China, from November 2017 to May 2018. Compared to the farmland, the forest plantation prolonged the retention of frozen soil because the shallower snow and the longer duration of snow cover in the forest contributed to a deeper frost depth and delayed soil thawing. The canopy also sheltered the frozen soil from the extreme fluctuations in freeze-thaw cycles (FTCs) during the snow-free period. Contrasting snow regimes and FTC dynamics contributed to variations in CO2 and N2O between the forest plantation and the farmland. Path analysis showed that the soil water content and soil temperature were the main regulators of N2O and CO2 emissions, respectively, in both land-use types. By contrast, soil substrate and microorganism biomass minimally influenced N2O and CO2 efflux. In conclusion, forest cover influences frozen soil dynamics and greenhouse gas emissions by buffering temperature fluctuations in both snow-covered and snow-free periods. This study further highlights the potential importance of anthropogenic land-use changes in influencing the cold season energy balance and gas efflux in future milder winter climates.