| Exoenzyme is an important type of soil enzymes, which passes through plasma membrane after synthesized in the cell and functions in free state in the environment. The decomposition of exoenzyme controls the material circulation of wetland ecosystem, which is the restricted step of the decomposition process of organic matters in wetland ecosystem.At present, the study of exoenzyme in sediment of wetland arises people's concerns increasingly. But the study has been rather dispersed due to the type diversity of wetlands, mainly focuses on the origin of exoenzyme, detection means, the temporal and spatial distribution, the effect of interference etc. but most of which is the study on terrestrial ecosystem.Research shows that exoenzyme is an important index of purification in wetland, but it still remains unclear on the differences of distribution and purification ability in different wetlands. There are lots of studies on the effect of the activities of exoenzyme by plants, but most of which is aiming at forest and agro-ecosystem, the study on exoenzyme in the plant community of estuarine tidal flat wetlands keeps untouched. There are little in the research between animals and the activities of exoenzyme. Existing studies are mainly on several soil animals in terrestrial ecosystem, the study involves in the effects of the exoenzyme activities influenced by macrobenthos remains untouched.The paper studied the ecological characteristics of four soil enzymes which are closely related to the circulation of nitrogen and phosphorus in Chongxi tidal flat wetland of Yangtze River Estuary through field observation and laboratory detection. The major conclusions drew on this study are:1. The study of the temporal and spatial distribution of the activities of exoenzyme and the function of water purification of exoenzyme in wetland indicated: Alkaline Phosphatase, Urease and Protease has significant functions in purification of nitrogen and phosphorus in wetland, the activities of exoenzyme is the highest in sediment of moderate opening wetland ecosystem, and have significant function in water purification. Correspondence analysis on the activities of exoenzyme in five sediments of Chongxi tidal flat wetland ecosystem, as well as nitrogen and phosphorus content by the means of field observation and laboratory detection from July, 2007 to March, 2008. The five types of wetlands includes Rivers connecting with the Yangtze River in Yangtze River and inland, Inland rivers not connecting with the Yangtze River, Inland shallow water lake and Tidal flat shallow water pond. The four indexes closely related to the circulation of nitrogen and phosphorus are Alkaline Phosphatase, Urease, Protease and Catalase. Analyzed on the temporal and spatial distribution of exoenzyme, and studied on the influence of purification function of nitrogen and phosphorus in wetland by the activities of exoenzyme.The results are as following:1) The differences of the temporal and spatial distribution in five sediments are significant. The average activity of the four exoenzymes in Inland shallow water lake is the highest, while the exoenzyme activity in Inland rivers not connecting with the Yangtze River is the lowest, the exoenzyme activity in 'Rivers connecting with the Yangtze River in Yangtze River and inland' and Tidal flat shallow water pond are in the middle level. This is probably because the activities of exoenzymes in the moderate opening wetland ecosystem is higher; In seasonal distribution, the activities of exoenzymes are higher in summer and autumn while the lowest in winter, the four exoenzymes are almost the same in the seasonal variation.2) Alkaline Phosphatase, Urease and Protease has significant functions in purification of nitrogen and phosphorus in wetland. There was a significant negative correlation between the activities of Alkaline Phosphatase and the contents of total phosphorus, soluble orthophate. The Correlation Coefficient is -0.989 and -0.981(p<0.01) respectively, And also there was a significant negative correlation between the activities of Urease, Protease and the contents of total nitrogen, ammonia nitrogen, the Correlation Coefficient is -0.954, -0.975, -0.992 and -0.997(p<0.01) respectively. High activities of exoenzyme corresponding to low contents of nitrogen and phosphorus.2. S studied the activities of exoenzymes in different types of plant communities of estuarine tidal flat wetlands including Herbaceous Plant, woody plant and mixed plant communities, the introduction of woody plants with mycorrhiz and developed root system can significantly improve the activities of exoenzymes in estuarine tidal flat wetlands.In January, 2006, we studied on the activities of exoenzymes in the plant communities of Chongxi tidal flat wetlands including Alnus trabeculasa- Phragmites communis, Taxodium distichum- Phragmites communis, Salix matsudana- Phragmites communis and pure Phragmites communis communities by the means of field observation and laboratory detection.Based on the results, we can conclude:1).Alkaline Phosphatase, Urease, Protease and Catalase has similar corresponding characteristics, the four exoenzymes activities are high or low at the same time.2). The four exoenzymes activities in Alnus trabeculasa- Phragmites communis community are higher than others while those in pure Phragmites communis community are the lowest, thus we concluded that for plants of hygrophytes with developed root system especially with mycorrhiz can significantly improve the activities of exoenzymes.3). Study on the activities of soil enzymes in the four plant communities, soil depth is 0-15cm, 0-15 cm, 15-30 cm, 30-50 cm and 50-70 cm respectively. Protease and Urease activities are both significantly decrease with the soil depth increased, the average decrease rate of urease activity is 61.93%, which is the most significant; Alkaline Phosphatase activity generally decreases with the soil depth increased, but reaches a peak in 15-30cm subsurface; There is little changes of Catalase activity.4) Compared with exoenzymes acitivities in the rhizosphere and non-rhizosphere of four plant communities, the average exoenzymes acitivities in the rhizosphere are higher than those in the non-rhizosphere.3. Study on the influence of exoenzymes of tidal flat wetland by C. dehaani.The burrowing behavior of macrobenthos can significantly improve the exoenzyme activities of tidal flat wetland and the contents of total nitrogen and total phosphorus. C. dehaani is a wide distribution macrobenthos in wetland of Yangtze River Estuary, the biomass in unit area are 13.20g AFDW·m-2 in Chongxi area, which is the highest among the common zoobenthos in the area. In Sept. 2007, we studied the exoenzymes activities and the contents of total nitrogen and total phosphorus by the means of field observation and laboratory detection.Based on the results:1) the activities of four exoenzymes in the feces of C. dehaani, cave soil, and non- contrast cave soil, and the contents of total nitrogen and total phosphorus increased with the elevation increased.2) the exoenzymes activities in the feces>those in the cave soil>those in the non-contrast cave soil, the difference is obvious(p<0.05). Thus we concluded that the burrowing behavior of C. dehaani can significantly improve the exoenzyme activities of tidal flat wetland.3).The total nitrogen total phosphorus in the feces>those in the cave soil>those in the non- contrast cave soil, the difference is obvious(p<0.05). Thus we concluded that the burrowing behavior of C. dehaani can significantly improve the contents of the total nitrogen total phosphorus of tidal flat wetland.
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