The community patterns and assembly mechanism varied in eukaryotic microorganisms with different cell sizes

Cell size is a fundamental determinant of eukaryotic microorganisms’ ecology, influencing community dynamics, physiological processes, and ecological interactions. However, it is still unclear whether eukaryotic microorganisms of different sizes have similar structural and assembly mechanisms. In this study, we sorted eukaryotic microorganisms’ cells into two sizes classes (cell size: >0.45 µm and 0.1–0.45 µm) and compared their structural and assembly mechanisms in the river. The results showed that there was no significant difference in the number of reads between two groups. The two size classes harbored distinct eukaryotic microorganisms’ communities. And large eukaryotic microorganisms’ cells had higher diversity compared to the small eukaryotic microorganisms’ cells. Assembly mechanisms of the two size classes were significantly different. We conclude that cell size is an important factor that determines eukaryotic microorganisms’ structure and assembly mechanisms. These findings underscore the critical role of cell size in determining eukaryotic microorganisms’ community and uncover a direct relationship between microbial morphology and ecological traits.