Fig. 3: Intracellular nitrate in diatom habitats and inside diatom cells.

a Diatom abundance and total diatom biovolume, b total ICNO3 contents, and c ICNO3 concentration inside diatom cells in water columns (blue), sediments (brown), microbial mats (green), and epilithic biofilms (cyan). Note different units for ICNO3 in b, c. Percent values in b give the median of the relative contribution of ICNO3 to total nitrate in each habitat type. Multiplication factors in c give the median of the enrichment of ICNO3 concentration inside diatom cells relative to freely dissolved nitrate (FDNO3) concentration in each habitat type. Box plots show median (solid line), 25th and 75th percentiles (box), and 10th and 90th percentiles (whiskers) of nA = 6–8 sampling sites within each habitat type and nB = 3 replicates each.