The Qinghai-Tibetan Plateau covers a vast area with a large variety of grassland ecosystems,which are considered to sequestrate significant CO₂ from the atmosphere and may play an important role in terrestrial carbon budget. To elucidate the potential strength of CO₂ exchange and its controlling factors, we examined ecosystem CO₂ fluxes in relation to environmental and biological factors for seven different Qinghai-Tibetan Plateau ecosystems with elevations ranging from 2800m to 5200m above sea level. These alpine ecosystems include alpine wetland, alpine meadow, alpine steppe, alpine shrublands and alpine desert. Ecosystem photosynthesis and ecosystem respiration were measured using a close chamber method under a wide range of light and temperature conditions from July to August, 2006. We assumed that all the ecosystems achieved peak aboveground biomass and maximum photosynthetic capacity during the measurement period.

Results/Conclusions

The results show that CO₂ fluxes, including gross ecosystem CO₂ uptake, net ecosystem CO₂ exchange and ecosystem respiration per unit ground area or per unit aboveground biomass, were highly heterogeneous across the ecosystems.  Daytime net ecosystem CO₂ uptake was highest in the alpine wetland in terms of the ground-area base, but highest in the alpine meadow on the basis of aboveground biomass. Results also indicate that soil moisture showed high correlation with different components of CO₂ fluxes among different ecosystems, while temperature and photosynthetic photon flux density determined the instantaneous ecosystem CO₂ fluxes in most ecosystems. The study suggests that soil moisture is the major determinant of ecosystem CO₂ fluxes on the plateau.  Moreover, spatial heterogeneity of ecosystem types must be considered to estimate the carbon budget on the Qinghai-Tibetan Plateau.