Marine Biology

, Volume 151, Issue 4, pp 1249–1259 | Cite as

Nitrate reductase and glutamine synthetase activity, internal N pools, and growth of Ulva lactuca: responses to long and short-term N supply

  • M. TeichbergEmail author
  • L. R. Heffner
  • S. Fox
  • I. Valiela
Research Article


Fast-growing macroalgae, including Ulva lactuca Linnaeus, respond rapidly to changes in nutrient conditions, particularly to short-term N supply. This ability to rapidly take up and assimilate N contributes to the increasing occurrence of macroalgal blooms in heavily N loaded coastal ecosystems. To determine whether long-term nutrient histories affect short-term responses in activity of N-assimilating enzymes, including nitrate reductase (NRA) and glutamine synthetase activity (GSA), internal N storage, and macroalgal growth, we conducted an in situ nitrate fertilization experiment between 7 and 22 July 2004, with fronds of U. lactuca collected from estuaries with high and low N loads in Waquoit Bay, Cape Cod, Massachusetts, USA (N 41° and W 70°). Initial NRA, GSA, % N, δ15N, and growth of U. lactuca fronds were higher in the site where nitrate was in high supply. Differences in NRA persisted even after short-term experimental enrichment. Differences in internal N pools, δ15N, and growth, in contrast, mirrored the changes of nutrient supply. The rate of turnover of the internal N content of U. lactuca was quite short (<2 d), and turnover of enzyme activity may have been even shorter. N isotopic fractionation by U. lactuca appeared to be of small magnitude, unlike the case of phytoplankton, and similar to that of vascular plants. δ15N was a better indicator of short-term response to external and internal nutrient supplies in U. lactuca than enzyme activity or N content, and may reliably detect rapid changes in N availability, source, and uptake and assimilation processes.


Specific Growth Rate Macroalgae Glutamine Synthetase Ulva Nitrate Reductase Activity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This research was supported by a NOS/ECOHAB grant, #NA16OP2728. This is ECOHAB publication # 169. This work was also supported in part by a Palmer McCleod Fellowship awarded to M. Teichberg, NSF REU support and Woods Hole Marine Science Consortium awarded to L. Heffner, and NOAA/NERRS and EPA STAR graduate fellowships awarded to S. Fox. The experiments comply with the current laws in the U.S.A. in which the experiments were performed.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • M. Teichberg
    • 1
    Email author
  • L. R. Heffner
    • 1
    • 2
  • S. Fox
    • 1
  • I. Valiela
    • 1
  1. 1.Marine Biological LaboratoryBoston University Marine ProgramWoods HoleUSA
  2. 2.Graduate School of OceanographyUniversity of Rhode IslandNarragansettUSA

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