The contamination of commercial 15N2 gas with 15N-labeled nitrate/nitrite and ammonium and consequences for nitrogen fixation measurements

<p>The data contained herein are associated with the manuscript, "The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements", which is available at PLOS ONE.</p> <p>We report on the presence of 15N-labeled nitrate/nitrite, ammonium, and nitrous oxide in commercial 15N2 gas and the enrichment of particulate nitrogen as a result of the biological assimilation of 15N labeled contaminants.</p

(a) δ¹⁵N_NH4 (log scale) of 5 µmol L⁻¹ ammonium solutions after equilibration with 0.1 mL ¹⁵N₂ gas from respective Sigma-Aldrich and Cambridge Isotopes lecture bottles <i>vs.</i> control solutions.

<p>Sigma-Aldrich treatments utilized 40 mL ammonium solutions, whereas Cambridge Isotopes treatments utilized 100 mL ammonium solutions. (<b>b</b>) δ¹⁵N_NH4 of higher sensitivity equilibrations of 5 µmol L⁻¹ ammonium solutions (10 mL) with 2.0 mL ¹⁵N₂ gas from Cambridge Isotopes lecture bottles <i>vs.</i> control solutions. n = the number of experimental replicates.</p

(<b>a</b>) δ¹⁵N_NO3+NO2 (log scale) of nitrate solutions (10–300 µmol L⁻¹) following equilibration with 0.1 mL ¹⁵N₂ gas from lecture bottles procured from three distributors.

<p>Solutions were 40 mL for Sigma-Aldrich and Campro Scientific equilibrations, and 100 mL for Cambridge Isotopes equilibrations. The solid line corresponds to the δ¹⁵N_NO3 of the control solutions for Sigma-Aldrich and Cambridge Isotopes experiments (δ¹⁵N_NO3 = 23.5±0.5‰); the dashed line corresponds to controls for Campro Scientific experiments (δ¹⁵N_NO3 = 14.15±0.1‰). Paired symbols identify replicate experimental treatments. (<b>b</b>) Corresponding apparent δ¹⁸O_NO3+NO2 of the experimental nitrate solutions. The solid line corresponds to the δ¹⁸O_NO3 of control solutions for the Sigma-Aldrich and Cambridge Isotope experiments (δ¹⁸O_NO3 = 18.9±0.3‰); the dashed line corresponds to controls for Campro Scientific experiments (25.4±0.3‰).</p

The δ¹⁵N of particulate nitrogen (δ¹⁵N_PN) of <i>D. tertiolecta</i> harvested in stationary phase following growth in media containing sodium nitrate (and no ammonium) and equilibrated with ¹⁵N₂ gas from Sigma Aldrich or Cambridge Isotopes.

<p>n = the number of experimental replicates.</p

(a) δ¹⁵N_NO3+NO2 (log scale) of higher sensitivity equilibrations of 10 µmol L⁻¹ nitrate solutions (10 mL) with 2 mL of ¹⁵N₂ gas from a Cambridge Isotopes or a Sigma-Aldrich bottle.

<p>(<b>b</b>) Corresponding apparent δ¹⁸O_NO3 (log scale) of higher sensitivity equilibrations of the two stocks. n = the number of experimental replicates.</p