Abstract: The export of terrestrial carbon via inland aquatic ecosystems is a key process in global carbon cycle. Carbon emission from streams is greater than average carbon emission from inland water bodies, affecting the regional and global carbon budget. We summarized the temporal change of partial pressure of carbon dioxide (pCO₂) and carbon dioxide flux (FCO₂) across water bodies and atmosphere. Both pCO₂ and FCO₂ showed significant diurnal and seasonal variations, and decreased with increasing stream order. We discussed the physical, hydrochemical, and biological factors affecting stream pCO₂ and FCO₂, such as flow velocity, pH, and aquatic biomass. The contribution of autochthonous organic carbon to FCO₂ increased with stream order, which was usually lower than 50%. We outlined the challenges in future research on stream carbon cycling, such as measurement technical problems and the lack of continuous monitoring over time. We hope this review could provide new ideas and future research directions to enhance our understanding on the role of streams in the global carbon cycle.

Key words: headwater, stream, partial pressure of carbon dioxide, carbon dioxide flux, dissolved organic carbon.