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The effect of nitrogen deprivation on stable isotope 15n fractionation and preference of ammonium, nitrate, and urea by marine dinoflagellates and a raphidophyte

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Title: The effect of nitrogen deprivation on stable isotope 15n fractionation and preference of ammonium, nitrate, and urea by marine dinoflagellates and a raphidophyte
Author: Sugimoto, Kugako
Degree Master of Science - MSc
Program Earth and Ocean Sciences
Copyright Date: 1998
Abstract: Nitrogen (N) preference and the uptake response of N-replete and N-starved dinoflagellate Amphidinium carterae and Prorocentrum micans, and the chloromonad (Raphidophyte) Heterosigma carterae grown on NH₄+1, NO₃-, and urea were determined by N disappearance rates and uptake rates. N-replete cells preferentially took up NH₄+ in the presence of three N forms. Urea was the second preference. NO₃- was taken up last. N-replete Heterosigma carterae exhibited a strong preference for NH₄+ uptake and its ratio of uptake preference of the three N sources relative to urea was 10 (NH₄+):0.1 (NO₃-):1 (urea). These ratios suggest a strong influence of NH₄+ on NO₃- uptake. However, the concentration of NO₃- decreased rapidly when only NO₃- and urea were present in a medium. This order of preference remained the same after N deprivation. However, N-deplete P. micans and A. carterae decreased their preference for NO3- relative to both NH₄+ and urea from 1.9 (NH₄+):0.6 (NO₃-):1 (urea) to 1.5:0.5:1 and from 6.9 (NH₄+):-0.2 (NO₃-):1 (urea) to 7.5:-1.1:1 respectively. On the other hand, N-deprived H. carterae increased its preference for NO₃- relative to both NH4+ and urea from 10 (NH₄+):0.1 (NO3-):1 (urea) to 7.5:0.2:1. The N uptake preference depended on the interactions of each N source. N-starved H. carterae in a batch culture grown on NH₄+ showed an immediate NH₄+ uptake after the re-addition of NH₄+ and ceased uptake for a short period and started to take up NH₄+ again. This NH₄+ uptake pattern existed, but was not evident in H. carterae grown on three N sources. Diel patterns of nitrate (NO₃-) uptake under a light:dark (14L:10D) cycle were investigated in a batch culture of H. carterae which is known as a diel vertical migrator. The concentration of NO₃- in the culture decreased mostly during light periods, and hardly decreased or even increased (i.e. efflux) during dark periods. NO₃--starved H. carterae showed NO₃- uptake during the dark period. NO₃--starved cells grown under a light:dark cycle exhibited a longer period of no uptake after the re-addition of NO₃- than when grown under continuous light. The impact of N deprivation on N isotope fractionation by marine phytoplankton grown on NH₄+, NO₃-, and urea, or only NO₃- was examined by using the predicted model of δ15N of particulate nitrogen (PN). The mechanism of isotope fractionation (ε) for P. micans, A. carterae, and H. carterae changed rapidly with N availability. The best fit ε(NH₄+) value for N-deprived A. carterae and H. carterae decreased from 20 and 24%o to 4 and < 4%o respectively following the re-supply of the three N sources while the ε(NH₄+) for P. micans increased from 12%o to 20%o. ε(NO₃-) for H. carterae grown on NO₃- also increased, probably due to the increased, efflux of dissolved organic N (DON) during the N deprivation. [Scientific formulae used in this abstract could not be reproduced.]
URI: http://hdl.handle.net/2429/9032
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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