Nitrogen and iron availability drive metabolic remodeling and natural selection of diverse phytoplankton during experimental upwelling: Supplementary Figures and Datasets

Nearly half of carbon fixation and primary production originates from marine phytoplankton, much of which occurs in episodic blooms in upwelling regimes. Here, we simulated blooms limited by nitrogen and iron by incubating Monterey Bay surface waters with sub-nutricline waters and inorganic nutrients and measured the whole-community transcriptomic response during mid- and late- bloom conditions. Cell counts revealed that centric and pennate diatoms (largely Pseudo-nitzschia and Chaetoceros spp.) were the major blooming taxa, but dinoflagellates, prasinophytes, and prymnesiophytes also increased. Viral mRNA significantly increased late-bloom and likely played a role in the bloom’s demise. Conserved shifts in the genetic similarity of phytoplankton populations to cultivated strains and reduction in the density of single nucleotide variants (SNVs) in late-bloom samples reflect decreases in intraspecific diversity as a result of competition and potentially indicate a selective sweep of adaptive alleles. We note differences between mid- and late-bloom metabolism and differential regulation of light-harvesting complexes (LHCs) under nutrient stress. While most LHCs are diminished under nutrient stress, we show that diverse taxa upregulated specialized, energy-dissipating LHCs in low iron. We also suggest the relative expression of NRT2 to GSII as a marker of cellular nitrogen status, and the relative expression of iron-starvation-induced proteins (ISIP1, ISIP2, ISIP3) to the thiamin biosynthesis gene (thiC) as a marker of iron status in natural diatom communities