The global abundance of picoplankton-rich Prochlorococcus and Synechococcus has a wide overlap of ecological niches, suggesting a long evolutionary history with similar physiological characteristics. The photophysiological characters of Prochlorococcus showed obvious vertical distribution, while the clades of Synechococcus had overlapping depth profiles. Based on this, we examined the physiological adaptation and comparative phylogeography of Prochlorococcus and Synechococcus clades in depth profiles. The Indian Ocean and South China Sea environmental factor data show that the concentrations of different macronutrients have the same vertical distribution, with distinct but opposite stratification of temperature and salinity. Picocyanobacteria was quantitatively isolated by 16S-23S internal transcriptional interval clonal library and qPCR. Through biogeography and linear co-occurrence analysis, we observed that the ecotypes of Synechococcus and Prochlorococcus have significantly similar depth profiles. At a certain depth, the upper layer distinguishes the ecotypes adapted to high light but low macronutrients, while the lower layer distinguishes the ecotypes adapted to low light but high macronutrients. The upper ecotypes are dominated by Prochlorococcus clade HLII and Synechococcus Clade II, while the lower ecotypes are alternately dominant, and the Synechococcus clade CRD1 is noteworthy. Overall, this study shows that Prochlorococcus and Synechococcus clades share common physiological adaptations and phylogeography in depth profiles.

Prochlorococcus,Synechococcus,Niche overlap