Nutrient availability is the main driver of nanophytoplankton phago-mixotrophy in North American lake surface waters

There has been limited research on the abiotic and biotic factors affecting the prevalence of phago-mixotrophy (prevMixo) among nanophytoplankton across freshwater ecosystems. In recent years, large-scale sampling campaigns like the EPA-National Lakes Assessment and the NSERC LakePulse survey have generated surface water community composition data for hundreds of lakes across North America, covering large environmental gradients. We present results from our analyses of the nanophytoplankton community data from these two surveys, focusing on a taxonomic comparison of the mixoplankton communities across ecoregions and multivariate analyses of the environmental drivers of the prevMixo. We identified potentially phago-mixotrophic taxa in the majority of sites and across all ecozones sampled. Lake trophic state was identified as the main predictor of nanophytoplankton resource-acquisition strategy assemblages, with lower prevalence and diversity of mixoplankton communities in more eutrophic lakes. Lake trophic state also controlled the composition of the mixoplankton community and increased total phosphorus levels were associated with a loss of mixoplankton diversity. This study represents the most comprehensive assessment of the prevMixo in lake nanophytoplankton communities to date spanning hundreds of sites and a dozen ecozones.