The utility of isotopic distributions in the environment is premised on knowledge of the magnitudes of isotope discrimination by individual biogeochemical reactions, which is most often gained through lab studies of cultured organisms. Our current focus is on the isotope effects of nitrate-consuming processes, in particular, nitrate assimilation by photosynthetic organisms (central to studies of nutrient supply and uptake in the surface ocean) and denitrification by heterotrophic bacteria (central to studies of the global ocean’s input/output budget of fixed N). While the core goal of this work is to help with environmental and paleoceanographic application of the N isotopes, the sensitivities of isotope effects also offer insight into cell physiology and enzyme mechanism.
Increase in nitrate δ15N and δ18O during nitrate assimilation by three species of diatoms and E. huxleyi grown under various environmental conditions. a) Change in nitrate δ15N relative to initial nitrate δ15N plotted as a function of 1n(f) (f being the fraction of initial nitrate that remains in the medium). The slopes of individual experiments approximate the N isotope effect on NO3-(15ε). Dashed lines show slopes for 15ε of 5 and 25‰. b) The δ15N vs. δ18O change in NO3-. The slope of the linear regression and its standard error (1.00 ± 0.01) are inclusive of all the experiments combined. Dashed lines show slopes of 1.1 and 0.9, for comparison. From Granger et al. (2004)
References
The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the…