Bacterioplankton Community Succession And The Control Factor Identification In Cascade Reservoirs

Bacterioplankton is the regulator of the global material cycle and plays an important role in the element biogeochemical cycle.Despite considerable attention has been paid to bacterioplankton in recent decades,little is known about the dynamic changes of bacterioplankton community and their influencing mechanisms in cascade reservoirs,which affects the comprehensive understanding of the ecological effects of cascade dam construction.Wujiang River is the largest water system in Guizhou Province,with high water level and abundant water energy resources.At present,it has completed the development of 11-level hydropower.For this reason,we take the Wujiang cascade reservoirs as the research object,using real-time fluorescence quantitative PCR and high-throughput sequencing technology to understand the spatial and temporal changes of bacterioplankton,and identify the environmental factors which control the changes.The main conclusions are as follows:?1?The annual water temperature?T??5.86²9.77°C?averaged 19.96°C;the pH?7.26⁹.30?averaged 7.84;the dissolved oxygen?DO??0.23¹9.92mg/L?averaged8.45mg/L.There were seasonal stratification of T,pH and DO in the column of the Wujiang cascade reservoirs.Generally speaking,the stratification started from April,and ended basically in October.The stratification phenomenon was most obvious in July.?2?The 16S rRNA abundance of bacterioplankton(1.53×10¹³¹.81×10¹⁷copies/L)in the Wujiang cascade reservoirs was 2.24×10¹⁶copies/L,and the seasonal difference was significant.The abundance was higher in January with a mean of5.31×10¹⁶copies/L and lower in October with a mean of 9.92×10¹⁵copies/L,respectively.According to Pearson correlation analysis,the 16S rRNA abundance of bacterioplankton in the surface water was positively correlated with ammonia nitrogen?NH₄-N?,pH and dissolved organic carbon,and negatively correlated with T and reservoir catchment area,respectively.The 16S rRNA abundance of bacterioplankton in the column water was positively correlated with NH₄-N,pH,DO and chlorophyll,and negatively correlated with total nitrogen?TN?,nitrate nitrogen?NO₃-N?,T,reservoir catchment area and water depth,respectively.?3?The dominant bacterioplankton phylum in the Wujiang cascade reservoirs were Proteobacteria,Actinobacteria,Bacteroidetes,Planctomycetes,Verrucomicrobia and Firmicutes,which accounted for 96.13%of the total.According to the NMDS analysis,the composition of bacterioplankton in the mainstream of the Wujiang River and the Sancha River and Maotiao River Basin was significantly different,and bacterioplankton community composition between the reservoirs of the Wujiang mainstream was small.The bacterioplankton diversity of the reservoirs was lower than that of the rivers,and the bacterioplankton diversity in the upper water of the reservoir column was higher than that of the lower layer.Through RDA analysis,we found that the composition of bacterioplankton in the surface water was mainly affected by TN,NH₄-N,reservoir catchment area,pH,T and DO,respectively,and TN was the most influential factor among them.The composition of bacterioplankton in column water was mainly affected by TN,NO₃-N,reservoir catchment area,pH and T,respectively,and the reservoir catchment area was the most influential factor among them.