Predominance of Precipitation and Temperature Controls on Ecosystem CO2 Exchange in Zoige Alpine Wetlands of Southwest China

Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured at Zoige wetland using the eddy covariance technique. Analysis of CO2 fluxes in two years showed Zoige wetland was a net CO2 sink of -47.1 and -79.7 g C m(-2) a(-1) in 2008 and 2009, respectively. The peak NEE value was -0.54 mg CO2 m(-2) s(-1) (the negative value signifies net ecosystem carbon gain from air). The maximal daily integrated NEE was -4.1 g C m(-2) d(-1) during the peak growth season (from July to August). Gross ecosystem photosynthesis was likely more variable than ecosystem respiration at both seasonal and interannual timescales in this wetland. Our data strongly suggested that the combination of precipitation and temperature, as well as phenological stage of vegetation, controlled the dynamics of ecosystem carbon gain, even in drought years. Therefore, an accurate representation of these parameters in climate models is critical to the success of forecasting carbon budgets of alpine wetlands.