I am interested in elucidating how physiological processes occurring on a microbial scale shape environmental processes on regional to global scales. I focus primarily on nitrogen cycling in marine systems, given the importance of N to ocean fertility, and also because N is the only plant nutrient whose biogeochemical cycling is effectuated entirely by biological processes. To evaluate N dynamics in the environment from the natural abundance ratios 15N/14N ratios of fixed N species. Individual biological N transformations in the N cycle show characteristic patterns in fractionation of the stable isotopes of N species, thus leaving an imprint on specific N pools. An important aspect of my work is to determine the imprints associated with biological N transformations, by growing mono-cultures of model micro-organisms to elucidate the physiological mechanisms underlying N and O isotope fractionation, and to determine the variability in the isotopic imprints and the sensitivity of the latter to various growth conditions. The patterns and pathways elucidated therein inform the interpretation of the distribution N and O isotope ratios in the environment, enabling to distinguish of the relative importance of particular N transformations. The distinct advantage of using N isotopic tracers to infer N cycling is that these integrate over spatial and temporal scales, and do not reflect bias otherwise introduced by bottle effects during on-deck incubations, and/or bias introduced by the inability to capture spatial and temporal variability from discrete on-deck rate measurements of biological N transformations.
 

Research Projects


Physio-ecology of marine plankton: N nutrition and N isotope fractionation -

Nitrate N and O isotope effects of a eukaryotic nitrate reductases in vitro -

Nitrogen biogeochemistry of the eastern Bering Sea shelf -

Nitrate isotope dynamics in the Arctic Ocean -
 

Current Students


Rich Dabundo - M.Sc. Student
Lija Treibergs - M.Sc. Student
 

Research Staff


Lija Treibergs
 

Publications


Granger, J., M. G. Prokopenko, D. M. Sigman, C. W. Mordy, Z. M. Morse, L. V. Morales, R. N. Sambrotto, and B. Plessen (2011), Coupled nitrification-denitrification in sediment of the eastern Bering Sea shelf leads to 15N enrichment of fixed N in shelf waters, J. Geophys. Res., 116, C11006, doi:10.1029/2010JC006751.

Prokopenko M. G., O. M. Pauluis, J. Granger, L. Y. Yeung (2011), Exact evaluation of primary production from the oxygen triple-isotope composition of O2: implications for the net-to-gross photosynthetic production ratios. Geophysical Research Letters 38, L14603, doi:10.1029/2011GL047652.

Granger, J., D. M. Sigman, M. M. Rohde, M. T. Maldonado, and P. D. Tortell (2010), N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures, Geochimica Et Cosmochimica Acta, 74(3), 1030-1040.

Granger, J., and D. M. Sigman (2009), Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method, Rapid Communications in Mass Spectrometry, 23(23), 3753-3762.

Granger, J., D. M. Sigman, M. F. Lehmann, and P. D. Tortell (2008), Nitrogen and oxygen isotope fractionation during dissimilatory nitrate reduction by denitrifying bacteria, Limnology and Oceanography, 53(6), 2533-2545.

Lehmann, M. F., D. M. Sigman, D. C. McCorkle, J. Granger, S. Hoffmann, G. Cane, and B. G. Brunelle (2007), The distribution of nitrate N-15/N-14 in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate, Geochimica Et Cosmochimica Acta, 71(22), 5384-5404.

Granger, J., D. M. Sigman, M. G. Prokopenko, M. F. Lehmann, and P. D. Tortell (2006), A method for nitrite removal in nitrate N and O isotope analyses, Limnology and Oceanography-Methods, 4, 205-212.

Sigman, D. M., J. Granger, P. J. DiFiore, M. M. Lehmann, R. Ho, G. Cane, and A. van Geen (2005), Coupled nitrogen and oxygen isotope measurements of nitrate along the eastern North Pacific margin, Global Biogeochemical Cycles, 19(4): GB4022.

Ward, B. B., J. Granger, M. T. Maldonado, K. L. Casciotti, S. Harris, and M. L. Wells (2005), Denitrification in the hypolimnion of permanently ice-covered Lake Bonney, Antarctica, Aquatic Microbial Ecology, 38(3), 295-307.

Armstrong, E., J. Granger, E. L. Mann, and N. M. Price (2004), Outer-membrane siderophore receptors of heterotrophic oceanic bacteria, Limnology and Oceanography, 49(2), 579-587.

Granger, J., D. M. Sigman, J. A. Needoba, and P. J. Harrison (2004), Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton, Limnology and Oceanography, 49(5), 1763-1773.

Granger, J., and B. B. Ward (2003), Accumulation of nitrogen oxides in copper-limited cultures of denitrifying bacteria, Limnology and Oceanography, 48(1), 313-318. 

Ward, B. B., J. Granger, M. T. Maldonado, and M. L. Wells (2003), What limits bacterial production in the suboxic region of permanently ice-covered Lake Bonney, Antarctica?, Aquatic Microbial Ecology, 31(1), 33-47.

Granger, J., and N. M. Price (1999), The importance of siderophores in iron nutrition of heterotrophic marine bacteria, Limnology and Oceanography, 44(3), 541-555.

Tortell, P. D., M. T. Maldonado, J. Granger, and N. M. Price (1999), Marine bacteria and biogeochemical cycling of iron in the oceans, Fems Microbiology Ecology, 29(1), 1-11.

Julie Granger

University of Connecticut Department of Marine Sciences
1080 Shennecossett Road Groton, CT 06340
Phone: (860) 405-9094
Fax: (860) 405-9153
email: julie.granger@uconn.edu