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.