|Nitrate reductase and glutamine synthetase activity, internal N pools, and growth of Ulva lactuca: responses to long and short-term N supply|Teichberg, M.; Heffner, L.R.; Fox, S.; 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. Mar. Biol. (Berl.) 151(4): 1249-1259. hdl.handle.net/10.1007/s00227-006-0561-4
In: Marine Biology. Springer: Heidelberg; Berlin. ISSN 0025-3162, more
|Authors|| || Top |
- Teichberg, M.
- Heffner, L.R.
- Fox, S.
- Valiela, I.
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, d15N, 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, d15N, 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. d15N 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.