[Effects of drying and wetting cycles induced by tides on net ecosystem exchange of CO over a salt marsh in the Yellow River Delta, China].

As a unique hydrological characteristic, the tidal action can strongly affect carbon balance in a salt marsh despite their short duration. Using the eddy covariance technique, we measured the net ecosystem CO exchange (NEE) and its environmental factors and tidal change over a salt marsh in the Yellow River Delta. It aimed to investigate the effect of tidal process and drying and wetting cycles induced by tides on NEE. The results showed that the tidal process promoted the daytime CO uptake, but it didn't clearly affect the nighttime CO release. Tidal inundation was a major factor influencing daytime NEE. The diurnal change of NEE showed a distinct U-shaped curve on both drought and wet stages, but not with substantial variation in its amplitude during the drought stage. The drying and wetting cycles enhanced the absorption of daytime CO. Under drought stage, the mean of the maximum photosynthetic rate (A), apparent quantum yield (α) and ecosystem respiration (R) were higher than those in wet stage. In addition, the drying and wetting cycles suppressed the nighttime CO release from the salt marsh but increased its temperature sensitivity.