Abstract: Diurnal variation of CO₂ flux from the Qinghai Lake alpine wetland ecosystem in summer was analyzed with the continuous eddy covariance technology,and factors affecting the variation were explored by taking into account meteorological observation data. Results show that: the CO₂ flux from the Qinghai Lake alpine wetland ecosystem varied in a U shape during a day in summer. During the time period from 8:00-20:00, CO₂ flux lingered below zero and during the remaining time period, it stayed above zero. Its lowest value appeared at 12:30, being -15.34μmol•m^-2•s^-1 and its daily mean value was -3.65μmol•m^-2•s^-1 (about-13.87 g•m^-2•d^-1), which indicates that the ecosystem is apparently an important carbon sink, absorbing CO₂. Correlation analysis of CO₂ flux with net radiation, air temperature and surface soil temperature shows that net radiation is the main factor affecting diurnal variation of CO₂ flux from the ecosystem in summer, and followed by air temperature and soil temperature. Multivariate regression analysis shows that the relationships of CO₂ flux with its affecting factors fit with the multiple linear regression equation, R²=0.689,and even reach a significant level(P<0.01).

Key words: eddy covariance, CO_２flux, alpine wetland ecosystem, Qinghai Lake