MEPS 179:291-296 (1999) - doi:10.3354/meps179291
Nitrogen isotopic fractionation during a simulated diatom spring bloom: importance of N-starvation in controlling fractionation
Nathalie A. Waser1,*, Zhiming Yu2, Kedong Yin1,**, Bente Nielsen1, Paul J. Harrison1, David H. Turpin3, Stephen E. Calvert1
**Present address: Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
ABSTRACT: N isotope fractionation ε was first determined during ambient NO3- depletion in a simulated diatom spring bloom. After 48 h of N-starvation, NH4+ was resupplied to the diatoms in small pulses to simulate grazer-produced N and then ε was determined. Large variations in ε values were observed: from 2.0-3.6 to 14-0o/oo during NO3- and NH4+ uptake, respectively. This is the first study reporting an ε value as low as 0 to 2o/oo for NH4+ uptake and we suggest that greater N demand after N-starvation may have drastically reduced NH3 efflux out of the cells. Thus the N status of the phytoplankton and not the ambient NH4+ concentration may be the important factor controlling ε, because, when N-starvation increased, ε values for NH4+ uptake decreased within 30 h. This study may thus have important implications for interpreting the δ15N of particulate N in nutrient-depleted regimes in temperate coastal oceans.
KEY WORDS: N isotope fractionation · 15N/14N · Nitrate uptake · Ammonium uptake · Diatoms · Spring bloom
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