Study Of The Microbial Community Structure In The Seawater And Benthic Environment Adjacent To The Changjiang Estuary

This dissertation introduced the definition of picoplankton,the general distribution situation of Synechococcus,picoeukaryotes,Prochlorococcus, heterotrophic bacteria and viruses in different oceans,expatiate the study actuality of marine benthos and the aim of this article.The development of flow cytometry and the principle of FACScan flow cytometry were introduced.The main approaches to analysis the picoplankton in the water sample were given out.The meathods to analysis the heterotrophic microorganisms in the sediment sample were studied via experiments and the primary process and several notices for the experiment were brought out.The picoplankton distribution in the Changjiang Estuary and adjacent areas were talked according to the field investigations of the hypoxia out of the Changjiang Estuary in 2006,the study of East China Sea shelf in November 2006 and February 2007 and the study of South China Sea(eastern of Hainan Island)in winter 2007 and summer 2008.Further more,the relationship between the hydrographic conditions and the community structures were discussed to further our understanding towards the significance of these microorganisms within marine biogeochemical sysles.From the distribution and correlations of hydrographic property,apparent oxygen utilization and the microorganisms' carbon biomass before and after hypoxia in 2006,we saw that the community structure changed evidently.The Synechococcus and viruses increased dramatically while the picoeukaryotes decreased.The relationship between the water pH,AOU and autotrophic to heterotrophic ratio indicated that,when the water column stratified well,the respiration of the microorganism and the decomposing of the organic matter depleted the water dissolved oxygen,which accelerated the hypoxia event.In addiation,the heterotrophic organism has more contribution to the microbial food loop under the hypoxia condition.The ECS shelf was mainly dominated by the Kuroshio water in winter.In the cruises of November 2006 and February 2007,the abundance of picoplankton community was about 10~3 magnitude and the heterotrophic bacteria and viruses abundance were about 10~5 magnitude.The Synechococcus and picoeukaryotes both had a dome shape in the surface water of the ECS shelf. The Prochlorococcus mainly distributed in the outer-shelf water with the low temperature and oligotrophic condition.The heterotrophic bacteria were considered to be the main contributor to the carbon pool.As the microorganism abundance decreased with the depth and all have close relationship with water temperature.The heterotrophic microorganisms can selectively make use of the organic and inorganic nutrients.The nutrient and the pico-phytoplankton decreased along the offshore ward and was supposed to be P limited in the ECS shelf.The study about Hainan Island showed that the Prochlorococcus was the primarily pico-phytoplankton in the South China Sea(eastern of Hainan Island). Heterotrophic microorganisms increased along the off shore ward.The Wanqyan River and Wenchang,Wenjiao River had different picoplankton community structure in winter and summer.The typhoon was supposed to be the propellant to cause the high abundance of picoplankton in fresh water in summer.With the study about the benthos in the Changjiang Estuary,ECS shelf and mangrove,we evidenced the high abundance(more than 10~6)of heterotrophic bacteria and viruses in the sediment.We can plot out four group benthos:the CDW influenced area,the Jiangsu-Zhejiang seacoast area,the ECS inner shelf and the ECS mid shelf.The abundance of heterotrophic bacteria and viruses and the sediment water content decreased with the sediment depth. The heterotrophic microorganisms had contribution with the decomposition of organisms and had close positive relationship with the sediment organic content.The heterotrophic bacteria and viruses had negative relationship in mangrove sediment while had positive relationship in shelf sediment.The viruses to bacteria ratio(VBR)reflected the sediment nutrient condition. Across the seacoast from the Chiang Estuary to the Taiwan Strait the VBR decreased,which image the resort and settlement process of nutrient in CDW influence area.