The Eubacterial Community Dynamics And The Significance On Nitrogen Cycling In Eutrophic Shenzhen Bay

Eutrophication is a process of too much input of organic matters to the river or bay,which contain a lot of nitrogen or phosphorus,resulted in excessive growth of macroalgae.It has been a serious issue which influenced the life of human beings and the security of the society.The microorganisms play an important role in the elementary biogeochemical cycling through micro food loop.In order to study the changing rule of ecosystems better and make proper decision for ocean management,the Lingdingyang River,the Yuen Long Sea,and the Shenzhen Bay Park Area,which specifically represented the mouth,the center and the top of Shenzhen Bay,which was recognized as classical eutrophic ocean,were chosen for investigating the ecological status,including obataining the information of environmental factors,the microbial abundance or biomass and the microbial community structures,to analyze the relationships between eubacterial dynamics and environmental factors' dynamics in 7 cruises during one year.Shenzhen Bay was seriously eutrophic,the water quality was still at inferior four type standard.We found that,except the pH value,other live physiochemical factors showed definitely significant difference;at the same time,the concentration of phosphate and total phosphorus excluded,other nutrient salts including nitrate,nitrite,ammonium,dissolved inorganic nitrogen and total nitrogen,all presented definitely significant changing trends with the the seasonal dynamics.However,neither the physiochemical parameters nor the nutrient salts,showed the difference among the sampling sites.The average abundance of planktonic bacteria in Shenzhen Bay during the four seasons in one year was 1.57×107 ind/mL.While the abundance of bacterioplanton in different sampling sites was changing between 6.00 ×106 ind/mL and 43.50 ×106 ind/mL.The average biomass of the bacterioplankton was 3.14×10-1?g/mL.The average biomass of bacterioplankton in different seasons was changed between 4.90×10-2?g/mL and 86.90×10-2?g/mL,while the average biomass in different sampling sites was changed between 2.29×10-1?g/mL and 3.69×10-1?g/mL.These results mean that Shenzhen Bay was eutrophic again.The microbial biomass showed significant difference in different seasons while no significant difference in all sampling sites.The bacterioplankton's biomass had strong relationship with the concentration of nitrite and ammonium.The microbial community structures were analyzed by terminal restriction fragments length polymorphism(TRFLP).The results showed that there were about 231 microbial species in the Shenzhen Bay planktonic bacteria community.Through the statistical methods like principle component analysis(PCA),cluster analysis(CA),the microbial seasonality was significantly discovered while the site difference was not.The results of canonical correlation analysis(CCA)verified the former conclusion.Contrast with other environmental factors,the concentration of all the nutrient salts related with nitrogen like the nitrate,dissolved inorganic nitrogen and total nitrogen,dominated the community structure of the bacterioplankton.To verify whether the abundance of eubacteria with specific functions from different sampling sites in the eutrophic bay was different or not,the expression concentration of microbial genes from sediments on nitrogen cycling in Lingdingyang River,Yuen Long Sea and Shenzhen Bay Park Area were identified by real time quantitative PCR.The results were that,NarG,NosZ and NirS in inner bay and the center of the bay were higher than the ones in the mouth of the bay.It is suggested that there were stronger denitrification in the top and center than the mouth of the bay.Furthermore,the concentrations of eubacteria which contained amoA in three sites were different,while the latter was 2 orders of magnitude lower than the eubacteria with former functional genes.It mean that there were more denitrification than ammonium oxidation in the whole bay.In the future,the problem of eutrophication would be solved gradually.All the results would further strengthen our recognition on the eubacteria in eutrophic bay and provide more useful suggestions on management of coastal ecosystem.