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Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton
Author(s) -
Granger Julie,
Sigman Daniel M.,
Needoba Joseph A.,
Harrison Paul J.
Publication year - 2004
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2004.49.5.1763
Subject(s) - nitrate , thalassiosira pseudonana , thalassiosira weissflogii , fractionation , nitrogen assimilation , phytoplankton , environmental chemistry , isotope fractionation , stable isotope ratio , nitrogen , chemistry , isotopes of nitrogen , water column , oceanography , nutrient , geology , chromatography , physics , organic chemistry , quantum mechanics
We report the first measurements of coupled nitrogen (N) and oxygen (O) isotopic variations of nitrate (NO ) during its assimilation by laboratory cultures of marine phytoplankton and derive the N and O kinetic isotope effects for nitrate assimilation by three species of diatoms ( Thalassiosira weissflogii , Thalassiosira oceanica , and Thalassiosira pseudonana ) and a coccolithophorid ( Emiliana huxleyi ). Large interspecies and intraspecies variations in the N isotope effects were observed. The O isotope effect associated with nitrate consumption was consistently close to the N isotope effect, such that the 18 O/ 16 O and 15 N/ 14 N of nitrate varied in a ratio of ~1 : 1, regardless of species or of the magnitude of the isotope effect. In addition, the 18 O/ 16 O and 15 N/ 14 N of internal nitrate of T. weissflogii grown under various environmental conditions were elevated relative to the medium nitrate by a proportion of ~1 : 1. These findings are consistent with a nitrate isotopic fractionation mechanism that involves nitrate reduction as the chief fractionating step. The observed N:O isotopic coupling during nitrate assimilation suggests that combined N and O isotopic measurements of water column nitrate can provide new constraints on the ocean N cycle.