Fig. 4.

UCYN-A symbioses fix ¹⁵N₂ in western Arctic waters. UCYN-A cell-specific ¹⁵N₂ fixation rates (A) and ¹⁵N enrichment (B–D) from nanoSIMS measurements after incubating natural populations in seawater with ¹⁵N₂. Bars of the same color (A) represent rates measured in individual symbioses (UCYN-A with host alga) from a single station and lineage (noted in underlying cell image). (Scale bar, 2 µm.) Averages are shown by a horizontal black line. Error bars are the SD of the cell-specific rate between the host and UCYN-A. Note the colored axes differ in scale on nanoSIMS images (B–D).