Non-growing season soil CO2 flux and its contribution to annual soil CO2 emissions in two typical grasslands in the permafrost region of the Qinghai-Tibet Plateau

• We investigate soil CO2 flux in Tibetan alpine meadow and swamp meadow.
• Non-growing season (NGS) accounted for a quarter of the annual soil CO2 emission.
• Swamp meadow emitted 57% more soil CO2 than alpine meadow in NGS.
• The Q10 of initial thaw and freeze period was higher than other seasons.
• Season-specific model was preferable for estimating the soil CO2 emission.

Non-growing season soil CO2 emissions are very important part of the annual C balance in the Arctic tundra ecosystems, but very limited information is available for the permafrost region of the Qinghai-Tibet Plateau, which hold great quantities of C. We conducted a full year measurement of soil CO2 flux in an alpine meadow and swamp meadow to quantify seasonal dynamics of non-growing season (include winter and initial thaw and freeze period (TFP)) soil CO2 flux and its contribution to annual soil CO2 emissions. Mean soil CO2 flux was higher in TFP (0.38–0.54 μmol m−2 s−1) than in winter (0.11–0.23 μmol m−2 s−1), with significant higher in swamp meadow than alpine meadow in the non-growing season. Soil temperature explained 76–85% of the yearly variation in the soil CO2 flux, with higher temperature sensitivity (Q10) in the TFP (5.67–9.43) than in other seasons (2.65–2.99). The cumulative non-growing season soil CO2 emission was 228–358 g CO2 m−2, accounted for 25–26% of annual emissions. The integrated contribution of non-growing season to annual emission based on season-specific, annual and growing season Q10 model were 26–27%, 32–34% and 44–45%, respectively, season-specific model may improve the accuracy of estimating the soil CO2 emissions. Our results indicate that non-growing season contributes a large portion of the annual soil CO2 emission in the permafrost region of the Qinghai-Tibet Plateau. Hence, estimating of annual C balance must consider the non-growing season soil CO2 emission, and should not neglect the soil CO2 emission of swamp meadow.