Effect of Scirpus mariqueter on nitrous oxide emissions from a subtropical monsoon estuarine wetland

The effects of the wetland plant Scirpus mariqueter on nitrous oxide (N₂O) emissions in Yangtze estuary, China, were investigated using an in situ static chamber technique. Field measurements spanned the entire growing season (May to October) and encompassed a wide range of weather conditions typical of the subtropical monsoon climate of this region. Simultaneous measurement of carbon dioxide (CO₂) and anatomical measurements were conducted to experimentally determine the gas transport mechanisms of S. mariqueter on N₂O flux. S. mariqueter had a significant effect on N₂O flux. Based on the comparison of light-dark and clipped-unclipped gas flux, N₂O flux was negatively correlated with NEE (p < 0.0001) and NPP (p < 0.001) under light conditions when S. mariqueter was present but positively with temperatures in the dark condition or when S. mariqueter was clipped. Besides the plant uptake corresponding to the N ₂O negative flux in light chamber, it is reasonable to assume that because of the limitation of nitrate in sediment, coupled nitrification- denitrification is the main process of N₂O producing. O₂ transported into the S. mariqueter rhizosphere during photosynthesis stimulated denitrifier also would consume the N₂O and would be induced to the N₂O diffusing from atmosphere into sediment. Although photosynthetic activity of S. mariqueter attenuated N₂O flux significantly over the course of the entire study period, creating a net sink for atmospheric N ₂O under light condition, the marsh of Chongming Island Dongtan wetland was a net source of atmospheric N₂O during the active S. mariqueter growth phase (averaged flux was 98.3 g N₂O m^-2 h^-1).