Two years of outdoor cultivation in alternate climates produces little divergence in the productivity of Nannochloropsis

Local environmental conditions may act as driving forces of natural selection and lead to trait divergence through time in outdoor microalgae cultures. In addition, microalgae phenotypes expressed outdoors may be modulated by other organisms, including pests and associated microbial communities. The present work builds on the long-term cultivation of a Nanochloropsis strain, across four geographically distinct field sites. The strain showed enhanced productivity at a site in California and decreased productivity at a site in New Mexico. The goal of the present work was to determine if those trait differences, among others, were the result of natural selection and evolution, phenotypic plasticity, or changes due to the influence of local microbiomes. To accomplish this goal, we coupled an outdoor common garden experiment in which cultivars from all four sites were grown at a single site in New Mexico with analyses of the algal microbiome. Our work revealed no differences in biomass productivity or biomass composition across strains in a common garden, suggesting that the parent strain exhibits high phenotypic plasticity, allowing growth across a wide range of climatic conditions. With respect to the microbiome, community composition and richness differed across cultivation system scales, parent and replicate ponds, and with and without pest management - but not greatly within the common garden. Our findings suggest that Nannochloropsis plasticity was driving the variation in phenotypic productivity responses to site-specific conditions and disturbances. This study helps in understanding the phenotypic changes and microbial community dynamics over years of cultivation.