Eukaryotic phytoplankton plays an important ecological function in river ecosystem. The 18S rRNA gene V4 variable region of the environmental samples in Liaohe river was sequenced by using 454 pyrosequencing technology. The reprehensive sequences of OTUs were annotated, and then the OTUs list was compared to the species list obtained by microscope observation. The phylogenetic tree was constructed based on the reprehensive sequences of OTUs and 18S rRNA genes of eukaryotic phytoplankton algae obtained from GenBank. The community structure characteristics of eukaryotic phytoplankton and its environmental impact indicators were further studied. In this study, we got 167901 high-quality sequences of 18S rRNA gene V4 region. These sequences were annotated to 424 OTUs, including 134 eukaryotic algae. The results of the high-throughput sequencing showed that bacillariophyta and chlorophyta were the dominant groups of the total phyla. The high-throughput sequencing also revealed the presence of Charophyta, Cryptophyta, Haptophyta and Chrysophyceae which were not observed by optical microscope. The phylogeny analysis clustered the Cryptophyta and Pyrroptata at phylum level. The different genera of Cryptophyta and part of families or genera of Pyrroptata were clustered and distinguished by phylogeny analysis. The results of RDA showed that NH4+-N, PO43-P and NO3- were the most important environmental factors that affected the community structure. This study provided a new perspective to understand the diversity, community structure and influence factors of eukaryotic phytoplankton in Liaohe river. The study also indicated that high-throughput sequencing has great application potential in investigation of phytoplankton and the water environment quality assessment in Liaohe river.
Keywords: 18S rRNA; community structure; diversity; eukaryotic planktonic algae; high-throughput sequencing.