Abstract: Freeze-thaw is a natural phenomenon at high elevation and high latitude, as well as some temperate regions. Many studies have shown that soil carbon dioxide (CO₂) emission flux is strongly influenced by freeze-thaw, indicating that soil CO₂ emission during freeze-thaw period is non-negligible in annual CO₂ emission. To better understanding the variations of CO₂ emission among terrestrial ecosystems during the freeze-thaw period, the effects of freezing temperature and freeze-thaw cycles on farmland, forest, wetland and grassland ecosystems were analyzed by collecting data from 37 papers published from 1990 to 2020. Compared to non-freeze-thaw treatment in the field condition, soil CO₂ emission under weak freeze-thaw treatment on farmland, forest, and grassland were increased by 44.2%, 25.5% and 56.0%, respectively, and was decreased by 10.1% in wetlands; while soil CO₂ emissions of four types of ecosystems under medium and strong freeze-thaw conditions were inhibited. In the laboratory condition, soil CO₂ emissions of the four ecosystems were promoted, with an average increase of 46.3%-272.5% under different freeze-thaw intensities, except for grassland ecosystem under the medium freeze-thaw condition. The peak value of soil CO₂ emission appeared at the early stage of freeze-thaw. After that, soil CO₂ emission rate gradually decreased to a stable level with increasing frequency of freeze-thaw cycles. This study helps to better understand the responses of soil CO₂ emissions from different ecosystems to freeze-thaw conditions and lays a foundation for further research.

Key words: freeze-thaw, carbon emission, carbon dioxide, ecosystem, meta-analysis.