Teichberg, Mirta ORCID: https://orcid.org/0000-0003-1586-738X, Heffner, L. R., Fox, S. and Valiela, I. (2007) Nitrate reductase and glutamine synthetase activity, internal N pools, and growth of Ulva lactuca: responses to long and short-term N supply. Marine Biology, 151 (4). pp. 1249-1259. DOI https://doi.org/10.1007/s00227-006-0561-4.

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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.

Document Type: Article
Programme Area: UNSPECIFIED
Research affiliation: Ecology > Algae and Seagrass Ecology
Refereed: Yes
Open Access Journal?: No
DOI: https://doi.org/10.1007/s00227-006-0561-4
ISSN: 0025-3162
Date Deposited: 03 Mar 2020 12:42
Last Modified: 01 Oct 2020 13:00
URI: http://cris.leibniz-zmt.de/id/eprint/3534

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