| The east Chongming tidal flat is an important wetland, which area has increased at speed of 200-300m/y. The significance of the tidal wetland is an international role, which lies in the estuary of the Yangtze River, land/ocean ecotones. There has been a relative intact vegetation succession gradient from Smooth Beach to 98 Levee: Smooth Beach, Scirpus mariqueter zone, Spartina alterniflora mosaic zone and Phraqmites australis zone. There have been many researches on wetland structure and function. Extracellular enzyme activities have the potential to affect all major wetland functions. Different kinds of extracellular enzymes (catalase, urease, protease, invertase, alkaline phosphatase) were chosen to explore these enzymes' function of different vegetation patterns and vertical sediments in tidal flat wetland ecosystem. Sediment characteristics measured included pH, particle diameter (PD), total phosphorus (TP), total nitrogen (TN), dissolved inorganic phosphorus (DIP) and organic matter (OM). The main results showed:1. There was more organic matter accumulated on the surface layer in the east Chongming tidal flat. The decomposition of OM was rather lower in tidal flat wetland sediments than other ecosystoms, for example agriculture, woods and grassland. Moreover, the tidal flat has produced much OM, and carried a great deal nutrient to the East Sea by the tide. Consequently the estuarine wetland has functioned not only as sinks for nutrients, but also as sources.2. The contents of TP, TN, OM of surface sediments increased gradually along the succession gradient, on the contrary PD, DIP decreased. The distribution of physico-chemical properties in the vertical section along different vegetation patterns showed: in Smooth Beach, TP, TN and OM were significantly lower than other zones; but DIP was higher than others. TP and OM were higher in the surface layer (0-1 Ocm) than other sections, but TN and DIP were higher in the subsurface layer (10-20cm). In zone of Scl, TN and OM increased with increasing sediment depths. In all the sampling sites, TP was lower in the subsurface layer than other sections, and DIP decreased gradually with increasing sediment depths and succession gradient.3. Catalase activities in the surface sediment increased along the succession gradient, and the lowest values were measured in Smooth Beach. In Smooth Beach and zone of Sc, catalase activities increased with increasing sediment depths. There were significantly correlations between catalase activities and physico-chemical properties (TP, r=0.792, p<0.01; DIP, r=-0.813, p<0.01; TN, r=0.962, p<0.01; OM,r0.936, p<0.01), which showed that catalase activities could reflect the conditions of nutrient and fertility of the sediments, and the activity might be an indicator of the condition of the vegetation communities' growth, and succession appraised.4. Urease activities in surface sediment had no changes along vegetation succession patterns. Urease activities decreased gradually with increasing sediment depths. However physico-chemical factors had no notable effect on urease activities.5. Invertase activities were much higher in the surface layer sediment. In zones of Sc and Ph, invertase activities decreased gradually with increasing sediment depths, in zone Sc invertase activities were much higher. Whereas in Smooth Beach the activities increased gradually with depths. In zone of Sp, invertase activities showed decreasing-increasing, and the highest value was at the lowest section (30-40cm). Positive correlation measured between invertase activities and OM (OM, r=0.474,p<0.01) showed that invertase activities could be an indicator of wetland fertility. The different vegetation patterns had no significant effect on invertase activities.6. Algae had exerted main influence on protease activities in east Chongming tidal flat wetland, so protease activities could reflect the abundance of algae in estuary wetland. There were significant negative correlation between protease activities and physico-chemical...
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