Exploring functional traits and functional diversity of mixotrophic phytoflagellates in small browned forest lakes—mixotrophy, phagotrophy and osmotrophy.

This article focuses on the role of mixotrophy—the combination of autotrophy and heterotrophy—in phytoplankton communities of small, humic forest lakes in Hungary. It emphasizes the inclusion of obligate osmotrophy, a form of heterotrophy involving direct uptake of dissolved organic molecules, as a significant trophic trait within mixotrophy, particularly in light-limited, browned lakes rich in allochthonous organic matter. Through large-scale sampling of 112 lakes, the study found that environmental factors such as chemical oxygen demand (COD), dissolved inorganic nitrogen (DIN), pH, and water color influence the dominance and functional traits of potential mixotrophs, which were predominantly nanoplanktonic, flagellated species exhibiting low functional diversity and suggesting functional redundancy. The findings highlight mixotrophy, including obligate osmotrophy, as an adaptive advantage over strict autotrophy in these ecosystems, while calling for further research to better classify mixotrophic species and understand their ecological roles.