Environmental Controls on Net Ecosystem CO2 Exchange Over a Reed (Phragmites australis) Wetland in the Yellow River Delta, China

Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R (eco)), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO2 emission was 1,657 g CO2 m(-2), while 2,612 g CO2 m(-2) was approximately accumulated as GPP, which resulted in the reed wetland being a net sink of 956 g CO2 m(-2). The ratio of R (eco) to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R (eco) during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R (eco), respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary.