UC San Diego

With increasing anthropogenic stressors affecting aquatic systems, it is becoming crucial to understand what factors promote and maintain phytoplankton populations and communities. Previous research shows that variation within phytoplankton microbiomes affects pairwise species interactions, but the full extent of the impacts that host microbiomes have on species-rich algal communities is not known. Our research aims to test if greater diversity in host-associated microbiomes increases algal community diversity and ecosystem functioning. Furthermore, our research goal is to determine if increased diversity in host-microbiomes will have a stronger effect on these metrics under more stressful conditions, including nutrient-depleted and warmer environments. This was tested by growing cultures consisting of five species of green eukaryotic algae in varying temperature, phosphorus, and microbiome diversity treatments for six weeks. Overall, our data did not support our hypotheses as cultures inoculated with the highest microbiome diversities did not promote the highest levels of algal community richness or biomass. Additionally, higher bacterial diversity did not mitigate the negative effects of phosphorus or temperature stress for algal communities. Our work empirically concludes that host microbiome composition is a critical factor that influences algal community dynamics and ecosystem functioning, and that it is environmentally dependent. This work develops our understanding of the various biotic and abiotic factors that govern species community composition, which will allow us to better predict how anthropogenic disturbances may affect our natural aquatic systems.