Abstract: We carried out in situ monitoring of methane (CH₄) fluxes of four ecosystems, alpine marsh, alpine meadow, alpine steppe, and alpine desert, in the Yushu Tibetan Autonomous Prefecture and Maduo County, with a portable greenhouse gas analyzer. Biomass, microorganism abundance, nutrients, soil moisture and temperature in each ecosystem were measured. These parameters were investigated to describe spatial-temporal variations in CH₄ flux and quantify the key influencing factors in all the ecosystems. The results showed that alpine marsh and alpine meadow were CH₄ sources, with the maximum flux in August. Alpine steppe and alpine desert were CH₄ sinks, with a minimum in August. During the growing season, there were significant differences in CH₄ flux among the four ecosystems (P<0.05). The abundance of mcrA gene in alpine marsh was highest, followed by alpine meadow, while the abundance of pmoA gene was highest in alpine meadow, followed by alpine marsh. The lowest abundances of mcrA and pmoA genes were found in alpine desert. There were significant differences in mcrA and pmoA among the four ecosystems (P<0.05). CH₄ flux in alpine marsh and alpine meadow was significantly positively correlated with soil temperature and mcrA (P<0.05), whereas CH₄ flux in alpine steppe and alpine desert was significantly negatively correlated with soil temperature and pmoA (P<0.05). Across all the ecosystems, CH₄ flux was significantly correlated with soil moisture, organic carbon, total nitrogen, biomass, mcrA and pmoA (P<0.05). Results of path analysis showed that soil organic carbon and the abundance of mcrA and pmoA had significant direct effects on CH₄ emissions, while soil temperature and water content indirectly affected it by changing soil microorganism abundances. Among all these key factors influencing CH₄ flux, the relative contribution of mcrA abundance was the highest (up to 30.53%), followed by organic carbon and biomass. The results indicated that variations in CH₄ flux among the different ecosystems were caused by differences in microorganism abundance, organic carbon, and biomass. It is therefore important to consider the heterogeneity of CH₄ emissions among different ecosystems when modeling and estimating CH₄ fluxes in alpine areas.

Key words: alpine ecosystem, methane flux, microbial abundance, organic carbon, biomass.