[Effect of environmental and biotic factors on net ecosystem CO₂ exchange over a coastal wetland in the Yellow River Delta]

Using the eddy covariance technique, we measured the net ecosystem CO₂ exchange (NEE) and its environmental and biotic factors over a coastal wetland in the Yellow River Delta to investigate the diurnal and seasonal variation in NEE and quantify the effect of environmental and biotic factors on NEE. The results showed that the diurnal change of NEE showed a distinct U-shaped curve during the growing season, but not with substantial variation in its amplitude during the non-growing season. During the growing season, the wetland acted as a significant net sink for CO₂, while it became carbon source during the non-growing season. On the scale of a whole year, the wetland functioned as a strong carbon sink of -247 g C·m^-2. Daytime NEE was mainly dominated by photosynthetically active radiation (PAR). Apparent quantum yield (α) and daytime respiration of ecosystem (R_eco,d) reached maximum in August, while maximum photosynthesis rate (A_max) reached its maximum in July. Nighttime NEE had an exponential relationship with air temperature (T_a). The mean value of temperature sensibility coefficient (Q₁₀) was 2.5, and it was positively related to soil water content (SWC). During the non-growing season, NEE was negatively correlated with net radiation (R_n), but not with other environmental factors significantly. However, during the growing season NEE was significantly correlated with R_n, T_a, soil temperature at 10 cm depth (T_{s 10}) and leaf area index (LAI), but not with aboveground biomass (AGB). Stepwise multiple regression analysis indicated that R_n and LAI explained 52% of the variation in NEE during the growing season.