[Genetic diversity of picoeukaryotic phytoplankton in the lakes along the middle-lower reaches of the Yangtze River]

The genetic diversity of picoeukaryotic phytoplankton in the 30 lakes along the middle-lower reaches of the Yangtze River was studied using flow cytometry combined with terminal restriction fragment length polymorphism (T-RFLP). The objectives of this study were to confirm the variance in the genetic diversity of picoeukaryotic phytoplankton among the lakes and to reveal its main affecting factors. Though the lakes investigated tended to or already were eutrophic, T-RFLP profiles of 18S rRNA gene fragments from picoeukaryotic phytoplankton showed high diversity. There were altogether 197 T-RFs detected from the lakes that we investigated, with 89 of them obtained in less than 3 lakes. Cluster analysis indicated their similarity was lower than 80%. Shannon-wiener diversity index showed that mesotrophic lakes contained more diverse picoeukaryotic phytoplankton community than eutrophic lakes. The canonical correspondence analysis revealed that the concentration of the total nitrogen had the most important impact on the picoeukaryotic phytoplankton communities (P =0. 006). The results showed that the genetic diversity of picoeukaryotic phytoplankton in the lakes were of great environmental heterogeneity and closely related to the trophic status. Two CCA axes can only explain 10.0% of the total variance in picoeukaryotic phytoplankton composition, suggesting that the evolution of picoeukaryotic phytoplankton was probably connected to the top-down manipulation as well.