The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate
In order to determine and understand the stable isotope fractionation of <sup>18</sup>O and <sup>15</sup>N manifested during assimilation of NO<sub>3</sub><sup>−</sup> in marine macro-benthic algae, two species (<i>Ulva</i> sp. an...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-11-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/6147/2014/bg-11-6147-2014.pdf |
| _version_ | 1818288541592977408 |
|---|---|
| author | P. K. Swart S. Evans T. Capo M. A. Altabet |
| author_facet | P. K. Swart S. Evans T. Capo M. A. Altabet |
| author_sort | P. K. Swart |
| collection | DOAJ |
| description | In order to determine and understand the stable isotope fractionation of
<sup>18</sup>O and <sup>15</sup>N manifested during assimilation of NO<sub>3</sub><sup>−</sup> in
marine macro-benthic algae, two species (<i>Ulva</i> sp. and
<i>Agardhiella</i> sp.) have been grown in a wide range of NO<sub>3</sub><sup>−</sup>
concentrations (2–500 μM). Two types of experiments were
performed. The first was one in which the concentration of the NO<sub>3</sub><sup>−</sup>
was allowed to drift downward as it was assimilated by the algae, between 24
hour replacements of media. These experiments proceeded for periods of
between 7 and 10 days. A second set of experiments maintained the
NO<sub>3</sub><sup>−</sup> concentration at a low steady-state value by means of a syringe
pump. The effective fractionation during the assimilation of the NO<sub>3</sub><sup>−</sup>
was determined by measuring the δ<sup>15</sup>N of both the (i) new algal
growth and (ii) residual NO<sub>3</sub><sup>−</sup> in the free-drift experiments after 0,
12, 24 and 48 h. Modelling these data show that the fractionation during
assimilation is dependent upon the concentration of NO<sub>3</sub><sup>−</sup> and is
effectively 0 at concentrations of less than ~2 μM. The
change in the fractionation with respect to concentration is the greatest at
lower concentrations (2–10 μM). The fractionation stablizes
between 4 and 6‰ at concentrations of between 50 and 500 μM.
Although the δ<sup>18</sup>O and δ<sup>15</sup>N values of NO<sub>3</sub><sup>−</sup> in the
residual solution were correlated, the slope of relationship also varied with
respect to NO<sub>3</sub><sup>−</sup> concentration, with slopes of greater than unity at
low concentration. These results suggest shifts in the dominant fractionation
mechanism of <sup>15</sup>N and <sup>18</sup>O between concentrations of 1 and
10 μM NO<sub>3</sub><sup>−</sup>. At higher NO<sub>3</sub><sup>−</sup> concentrations
(>10–50 μM), fractionation during assimilation will lead to
δ<sup>15</sup>N values in algal biomass lower than the ambient NO<sub>3</sub><sup>−</sup>
and <sup>15</sup>N enrichments in the residual NO<sub>3</sub><sup>−</sup>. |
| first_indexed | 2024-12-13T01:58:01Z |
| format | Article |
| id | doaj.art-b9f560c53a1041cea24cbb4f42bb1c01 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-13T01:58:01Z |
| publishDate | 2014-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-b9f560c53a1041cea24cbb4f42bb1c012022-12-22T00:03:21ZengCopernicus PublicationsBiogeosciences1726-41701726-41892014-11-0111216147615710.5194/bg-11-6147-2014The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrateP. K. Swart0S. Evans1T. Capo2M. A. Altabet3Division of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, Fl 33149, USADivision of Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, Fl 33149, USADivision of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, Fl 33149, USASchool for Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, MA 02744, USAIn order to determine and understand the stable isotope fractionation of <sup>18</sup>O and <sup>15</sup>N manifested during assimilation of NO<sub>3</sub><sup>−</sup> in marine macro-benthic algae, two species (<i>Ulva</i> sp. and <i>Agardhiella</i> sp.) have been grown in a wide range of NO<sub>3</sub><sup>−</sup> concentrations (2–500 μM). Two types of experiments were performed. The first was one in which the concentration of the NO<sub>3</sub><sup>−</sup> was allowed to drift downward as it was assimilated by the algae, between 24 hour replacements of media. These experiments proceeded for periods of between 7 and 10 days. A second set of experiments maintained the NO<sub>3</sub><sup>−</sup> concentration at a low steady-state value by means of a syringe pump. The effective fractionation during the assimilation of the NO<sub>3</sub><sup>−</sup> was determined by measuring the δ<sup>15</sup>N of both the (i) new algal growth and (ii) residual NO<sub>3</sub><sup>−</sup> in the free-drift experiments after 0, 12, 24 and 48 h. Modelling these data show that the fractionation during assimilation is dependent upon the concentration of NO<sub>3</sub><sup>−</sup> and is effectively 0 at concentrations of less than ~2 μM. The change in the fractionation with respect to concentration is the greatest at lower concentrations (2–10 μM). The fractionation stablizes between 4 and 6‰ at concentrations of between 50 and 500 μM. Although the δ<sup>18</sup>O and δ<sup>15</sup>N values of NO<sub>3</sub><sup>−</sup> in the residual solution were correlated, the slope of relationship also varied with respect to NO<sub>3</sub><sup>−</sup> concentration, with slopes of greater than unity at low concentration. These results suggest shifts in the dominant fractionation mechanism of <sup>15</sup>N and <sup>18</sup>O between concentrations of 1 and 10 μM NO<sub>3</sub><sup>−</sup>. At higher NO<sub>3</sub><sup>−</sup> concentrations (>10–50 μM), fractionation during assimilation will lead to δ<sup>15</sup>N values in algal biomass lower than the ambient NO<sub>3</sub><sup>−</sup> and <sup>15</sup>N enrichments in the residual NO<sub>3</sub><sup>−</sup>.http://www.biogeosciences.net/11/6147/2014/bg-11-6147-2014.pdf |
| spellingShingle | P. K. Swart S. Evans T. Capo M. A. Altabet The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate Biogeosciences |
| title | The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| title_full | The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| title_fullStr | The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| title_full_unstemmed | The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| title_short | The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| title_sort | fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate |
| url | http://www.biogeosciences.net/11/6147/2014/bg-11-6147-2014.pdf |
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