Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Project Information
• Funding

The delta 15N of Dunaliella tertiolecta organic matter after growth in media equilibrated with 15N2 gas.

Refer to the following publication for more information:
Dabundo, R., Lehmann, M.F., Treibergs, L., Tobias, C.R., Altabet, M.A., Moisander, P.H., and Granger, J. 2014. The Contamination of Commercial 15N2 Gas Stocks with 15N–Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements. PLoS ONE, 9(10): e110335. doi:10.1371/journal.pone.0110335

See related datasets:
delta 15N NO3
delta 15N NH4
direct N2O
N2

Data was acquired from an isotope ratio mass spectrometer using Isodat 3.0 software.

Particulate Nitrogen calculations:
The equation describing the linear regression of the standards' observed delta 15N PN and Assigned delta 15N (obs = x and assigned = y) was used to calculate delta 15N PN (y) of the samples from the uncorrected delta 15N (x).

Refer to the following publication for more information:
Dabundo, R., Lehmann, M.F., Treibergs, L., Tobias, C.R., Altabet, M.A., Moisander, P.H., and Granger, J. 2014. The Contamination of Commercial 15N2 Gas Stocks with 15N–Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements. PLoS ONE, 9(10): e110335. doi:10.1371/journal.pone.0110335

Summary of methods from Dabundo et al. 2014:
Reagents:
Four lecture bottles of 98+ at% 15N-labeled N2 gas were purchased from Sigma-Aldrich, three from lot # SZ1670V, and one from lot # MBBB0968V. Two 1L lecture bottles of 98+ at% 15N2 were purchased from Cambridge Isotopes from lot #’s I1-11785A and I-16727. One 1L lecture bottle of 98+ at% 15N2 was purchased from Campro Scientific from lot # EB1169V. Ammonium and nitrate solutions were prepared with salts or with solutions obtained from different distributors: sodium nitrate (NaNO3), potassium nitrate (KNO3), and ammonium chloride (NH4Cl) from Fisher Scientific; analytical-grade potassium nitrate from Fluka Analytical and a gravimetric solution of ammonium chloride from SPEX CertiPrep.

Dunaliella tertiolecta cultures:
The marine green alga Dunaliella tertiolecta was cultured in growth media equilibrated with 15N2 gas in order to ascertain the susceptibility of 15N-labeled gas contaminants to assimilation by non-N2-fixing organisms. Culture medium was prepared from filtered Long Island Sound sea water supplemented with 50 umol/L NaNO3, 36.3 umol/L NaH2PO4*H2O, and 107 umol/L Na2SiO3*9H2O, as well as f/2 trace metals and f/2 vitamins, added from filter sterilized stock solutions. Medium (200 mL) was dispensed in 250 mL stoppered glass bottles. Experimental treatment bottles were equilibrated overnight with 0.2 mL 15N2 gas from either a Cambridge Isotopes or Sigma-Aldrich lecture bottle. Following inoculation, cultures were left loosely capped and placed on a windowsill with exposure to natural light. Nitrate concentrations were monitored daily. Upon the complete depletion of nitrate, 8 days after inoculation, the cultures were harvested on pre-combusted GF/F filters. Filters were dried at 60 degrees C for 18 hours pending N isotopic analysis of the particulate nitrogen.

Particulate nitrogen isotope ratio analyses:
The d15N of particulate nitrogen (PN) was analyzed using a Costech Instruments elemental combustion system (model 4010) coupled to a Thermo Scientific Delta V Advantage IRMS. Analyses were standardized using L-glutamic acid reference materials, USGS-40, and USGS-41.

Samples with the same ID are replicated measurements.

BCO-DMO Edits:
- Modified parameter names to conform with BCO-DMO naming conventions;
- Denoted 'Control' and 'Standard' in the lot_number column;
- Replaced spaces with underscores.
- Replaced blanks (missing values) with 'nd' to indicate 'no data'.

Description from NSF award abstract:
This study will test the sensitivity of the amplitude of the denitrification isotope effect to culture conditions pertinent to the ocean environment. The isotope effect amplitude will be explored with respect to electron donor, trace oxygenation, and temperature, in both batch and continuous culture experiments of denitrifiers. The proposed work will also involve measurements of the enzymatic isotope effect of the respiratory nitrate reductase of denitrifiers, measurements of its enzymatic activity among cultures, and examination of cellular nitrate transport kinetics of denitrifying strains. The experiments are designed to reveal the physiological basis of the modulation of the isotope effect amplitude, which will further resolve this manifestation in the environment.

In regards to the broader significance and importance of this study, these new experimental data will provide a basis for integration of nitrogen isotope dynamics in ocean models to test how key environmental parameters can affect the global ocean distribution of nitrogen isotopes.