Abstract: We measured in situ CH₄ and CO₂ fluxes of alpine grassland, marsh meadow, and alpine marsh using portable greenhouse gas analyzer in Longbaotan, a nature reserve located in the middle of Qinghai-Tibet Plateau, in two growing seasons from 2017 to 2018. Our objectives were to determine the differences in CH₄ and CO₂ fluxes among the three ecosystems and their influencing factors. The results showed that marsh meadow and alpine marsh were CH₄ sources in both growing seasons, with an emission peak in July-September. The alpine grassland was a CH₄ sink, with an absorption peak in August. CH₄ flux in alpine grassland significantly differed from that in marsh meadow and alpine marsh (P<0.05). All the three ecosystems were the sources of CO₂ and the emission peak appeared from June to August. The annual mean value of CO₂ flux was the largest in alpine grassland and the lowest in alpine marsh (P<0.05). CO2 fluxes in alpine grassland and alpine marsh were significantly negatively correlated with CH₄ fluxes (P<0.01), and a positive correlation was found in marsh meadow (P=0.02). Results of principal component analysis showed that the first principal component was soil factor, the second was biological factor, and the third was temperature factor. Results from stepwise regression showed that soil temperature was the key factor affecting CH₄ flux, and soil temperature and humidity were the key factors of CO2 flux on monthly scale. Results from Pearson correlation analysis showed that the CO₂ flux of the three ecosystems was significantly positively correlated with soil temperature (P<0.01), negatively correlated with soil moisture (P<0.05). The CH₄ flux was significantly positively correlated with soil moisture (P<0.01). The heterogeneity of CH₄ and CO₂ fluxes in alpine grassland, marsh meadow and alpine marsh was caused by temperature, soil moisture, soil organic matter and nitrogen. When estimating CH₄ and CO₂ emissions in the Qinghai-Tibet Plateau, the difference of carbon emissions from different ecosystems should be considered.

Key words: central Qinghai-Tibet Plateau, alpine grassland, alpine marsh, CH₄ flux, CO₂ flux.