Study On Eukaryotic Ultra-phytoplankton Diversity, Population Genetics Structure And Its Relationships With Environmental Factors In The Three Gorges Reservoir

The Three Gorges Reservoir of China is remarkable water conservancy project.Reservoir impoundment has many inevitable impacts on reservoir water environment and its ecological system. It is significant to study the dynamic of the reservoir ecological system and phytoplankton distribution. Phytoplankton plays an important role of primary producers in the water ecological system. This study was carried out to study eukaryotic ultra-phytoplankton community structure and its relationships with environment physical and chemical factors.In this study, Sanger-based clone libraries of the 18 S rRNA gene were used to analyze the eukaryotic ultra-phytoplankton diversity from five sampling sites along the Changjiang main stream of Hubei province and Xiangxi bay of the Three Gorges Reservoir in four seasons of 2013. Using amplified rDNA restriction fragment analysis and combined with sequencing analysis, eukaryotic ultra-phytoplankton biodiversity of the Changjiang main stream and Xiangxi bay of the Three Gorges Reservoir was studied. Correlations between eukaryotic ultra-phytoplankton communities and environmental factors were analyzed using the redundancy analysis(RDA).Results of clone libraries revealed a high diversity among eukaryotic ultra-phytoplankton assemblages. The eukaryotic phytoplankton diversity distribution of the Changjiang main stream and Xiangxi bay showed obvious differences between time and space, Changjiang main stream had a significant space scale difference, and the space-time difference of the Xiangxi bay biodiversity mainly reflected in time scales. The community composition of eukaryotic ultra-phytoplankton was very different between Changjiang main stream and the Xiangxi bay.In Xiangxi bay, the community captured by our research was dominated by three main phyla, Cryptophyta, Chlorophyta, and Ciliophora(69.6% of clones), ten additional phytoplankton groups were found at <5% clonal abundance. For example, Dinozoa, Telonema,Cercozoa and Haptophyta were also found, albeit in low abundances. A significant number of sequences did not show a close affiliation with any known class of organisms. One of the advantage of Changjiang main stream is Cryptophyta, and the advantage of Xiangxi bay were Cryptophyta and Chlorophyta. The diversity index(Shannon index) was highest in autumn,which suggested that the eukaryotic ultra-phytoplankton biodiversity was most abundant in autumn. Further analysis showed that the compositions of picoeukaryotic assemblages were also most variable between different sampling sites or seasons. As for the relationships between environmental factors and the distribution of eukaryotic ultra-phytoplankton,Cryptophyta with ORP and dissolved oxygen were positively correlated in Changjiang main stream, phyla of Cryptophyta and Chlorophyta with N-NH4 were positively correlated in Xiangxi bay, Cryptophyta had a negative correlation with COD in all of Changjiang main stream and Xiangxi bay of Hubei province.